































Ecology, Economy and Society–the INSEE Journal 8(2): 33-66, July 2025 

 

RESEARCH PAPER 

The Ecological and Socio-economic Impacts of the 
Aquarium Sailfin Catfish Invasion: Fate of Fisherfolk 
at Major Inland Water Bodies, Tamil Nadu, South 
India  
Mohan Raj Rajasekaran, Indhar Saidanyan Ravichandran, Parthiban 

Balasingam, and Chandrasekaran Sivagnanam 

Abstract: Keeping pets has been part of human life since the earliest civilizations. 
Today, exotic animals are sold online and shipped globally to enthusiasts. However, 
pet sellers and keepers sometimes release exotic pets into nearby natural 
ecosystems, leading to biological invasion. This paper examines the invasion by 
sailfin catfish (Pterygoplichthys spp.) of the Cauvery and Vaigai river basins and its 
ecological and socio-economic impacts. We assessed the ecological impacts by 
comparing the total abundance and biomass of the invasive fish species (IFS), 
Pterygoplichthys spp., with those of comparator fish species (CFS) and various 
physicochemical parameters. We used semi-structured interviews and case studies 
of IFS mechanical removal programmes to assess the socio-economic impacts. The 
abundance and biomass of the IFS were significantly higher than those of the CFS 
in most lentic and lotic ecosystems. Interviews revealed significant sociological 
impacts on fisherfolk, including a push from fishing (a familial profession) to non-
fishing vocations. The input–cost–outcome assessment of mechanical removal 
programmes revealed that the expenditure incurred could not prevent further 
invasion of the IFS. This study advocates for increasing awareness among 
stakeholders to devise effective control measures and implement policy-level 
changes to curb the sailfin catfish invasion in India’s inland water bodies. 

Keywords: Pterygoplichthys spp., Biological Invasion, Ecological and Socio-economic 
Impacts, Fishing Communities, Cauvery River Basin, Vaigai River Basin. 

 

 Department of Plant Sciences (DPSc), School of Biological Sciences (SBS), Madurai 
Kamaraj University, Madurai - 625021, India (MKU); santhamoorthy92@gmail.com  

 DPSc, SBS, MKU; saidanyan@gmail.com  

 DPSc, SBS, MKU; parthibanpana@gmail.com 

 DPSc, SBS, MKU; csekaran.biological@mkuniversity.ac.in.  

Copyright © Rajasekaran, Ravichandran, Balasingam, and Sivagnanam 2025. Released under 
Creative Commons Attribution © NonCommercial 4.0 International licence (CC BY-NC 

4.0) by the authors.  

Published by Indian Society for Ecological Economics (INSEE), c/o Institute of Economic 

Growth, University Enclave, North Campus, Delhi 110007.  

ISSN: 2581–6152 (print); 2581–6101 (web).  

DOI:  https://doi.org/10.37773/ees.v8i2.1191  

mailto:santhamoorthy92@gmail.com
mailto:saidanyan@gmail.com
mailto:parthibanpana@gmail.com
mailto:csekaran.biological@mkuniversity.ac.in
https://doi.org/10.37773/ees.v8i2.1191


Ecology, Economy and Society–the INSEE Journal [34] 

 

1. INTRODUCTION 

Humans have been fascinated with pet-keeping since time immemorial 
(Herzog 2014; Gee and Mueller 2019). Recent reports show that nearly 50% 
of households in the US, Australia, and the UK keep at least one pet in 
their homes for recreational purposes (Lockwood et al. 2019). The COVID-
19 pandemic lockdowns also led to an increase in the adoption of exotic 
pets as a means of alleviating stress (May 2021; Hoffman et al. 2021; 
Shoesmith et al. 2021). The pet and aquarium trade has become a 
multibillion-dollar industry worldwide. For instance, the US reptile industry 
generated nearly $1.4 billion in annual revenues in under two decades since 
1990 (Collis and Fenili 2011). Similarly, the global trade in ornamental fish, 
fish feed, and accessories is estimated to exceed $15 billion, with significant 
year-over-year growth (Borges et al. 2021).  

In the past, conventional retail pet and aquarium shops were the primary 
pathway for acquiring exotic pets, including small animals, birds, aquatic 
plants, and ornamental fish. Subsequently, these organisms were released 
into freshwater and marine ecosystems globally, either intentionally or 
accidentally (Krishnakumar et al. 2009; Lockwood et al. 2019). Currently, the 
online pet or aquarium trade, facilitated by online pet shops, e-commerce 
sites (Soundararajan et al. 2015), and social media platforms (Borges et al. 
2021), has become a novel pathway for acquiring exotic pets. This has 
accelerated the introduction of a vast variety of exotic organisms, especially 
freshwater and marine fish, at an unprecedented rate in the global pet 
market. For instance, Soundararajan et al. (2015) report that almost 1,000 
varieties of exotic ornamental fish were already being traded online in India 
a decade ago. Similarly, Borges et al. (2021) report that approximately 600 
species of marine and freshwater ornamental fish are sold online through 
Facebook in Brazil. 

In the global ornamental fish trade, freshwater fish are the dominant 
species, accounting for approximately 90% of the total traded volume, 
primarily due to their popularity and widespread use as aquarium pets, 
compared to marine fish and invertebrates (King 2019; Valdez and 
Mandrekar 2019). Due to the aquarium trade, ornamental fish comprise 
one-third of the world’s worst aquatic invasive species. The aquarium fish 
invasion occurs through the release of unwanted fish and accidental escapes 
from tanks, breeding farms, and public aquariums into nearby drainage 
systems connected to natural aquatic habitats (Padilla and Williams 2004; 
Soundararajan et al. 2015). Sometimes, fish are intentionally released in 
temple ponds as part of religious rituals (Severinghaus and Chi 1999). From 
the public’s perspective, aquarium pets have become an integral part of life. 



[35] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

However, aquarium keepers often encounter challenges in relocating these 
exotic organisms when they move for jobs, education, business reasons, 
vacations, or medical treatments. In such cases, aquarium keepers attempt 
to give their exotic pets to relatives or friends or release them into nearby 
natural ecosystems (Duggan et al. 2006; Stringham and Lockwood 2018). 
These repeated introductions ultimately result in bioinvasion, which leads to 
substantial environmental and economic losses worldwide. For instance, 
Diagne et al. (2021) estimated that the global economic losses associated 
with bioinvasion were a minimum of $1.288 trillion over the period 1970–
2017. Exotic fish species, such as Oreochromis mossambicus (Mozambique 
tilapia), Gambusia affinis (mosquitofish), Osphronemus goramy (giant gourami), 
Xiphophorus maculatus (southern platyfish), and Poecilia reticulata (guppy), have 
invaded Indian rivers due to the aquarium trade and subsequent multiple 
introduction events (Raghavan et al. 2008). 

Pterygoplichthys spp. (sailfin catfish) are one such popular freshwater 
aquarium fish. Commonly called tank cleaners, these fish are native to 
South America, especially the Amazon River Basin, and have been 
introduced into local ecosystems in many parts of the world. These are 
reported as an invasive species in over 20 countries, including India 
(Krishnakumar et al. 2009; Sinha et al. 2010; Global Invasive Species 
Database 2025). In India, four species, including Pterygoplichthys anisitsi, P. 
disjunctivus, P. multiradiatus, and P. pardalis, have been observed in various 
freshwater habitats, including rivers, lakes, ponds, and canals (Singh and 
Lakra 2011; Sarkar et al. 2012; Soundararajan et al. 2015; Ganguly and 
Umapathy 2024; Verma et al. 2024; Wanjari et al. 2024). These invasive fish 
species are problematic because they occupy typical fishing habitats, 
resulting in low yields and destroying fishing nets (Chavez et al. 2006; 
Wakida-Kusunoki et al. 2007), which ultimately affects the revenue and 
protein intake of inland fishing communities. Though scattered news 
reports and literature (Sinha et al. 2010; Bijukumar et al. 2015; Muralidharan 
et al. 2015; Raj et al. 2021; Daniel et al. 2022; Wanjari et al. 2024; Hussan et al. 
2025) are available on the invasion and subsequent impact of Pterygoplichthys 
spp., comprehensive studies about their habitat characteristics and 
ecological and socio-economic impacts are limited in the Indian context. 
Therefore, in this study, we examine the ecological and socio-economic 
impacts of the Pterygoplichthys spp. invasion in two major river basins, the 
Cauvery and Vaigai of Tamil Nadu, with the following objectives: i) to 
study the distribution of the invasive fish species (IFS) Pterygoplichthys spp.; 
ii) to assess the ecological impacts of the IFS; iii) to investigate the influence 
of water physicochemical characteristics on the abundance and biomass of 



Ecology, Economy and Society–the INSEE Journal [36] 

 

IFS; and iv) to reveal the socio-economic impacts faced by fisherfolk due to 
the Pterygoplichthys spp. invasion. 

 

2. MATERIALS AND METHODS 

The materials used and methodology followed for the field survey, 
measurement of water physicochemical characteristics, ecological and socio-
economic impact assessments of the Pterygoplichthys spp. invasion in the 
Cauvery and Vaigai river basins, and the statistical data analysis is detailed in 
the following subsections. 

2.1. Study Site and Field Survey 

Initially, extensive field surveys were conducted at several inland water 
bodies around the Cauvery River Basin (CRB) and Vaigai River Basin 
(VRB), Tamil Nadu, South India, to record the presence of invasive 
Pterygoplichthys spp. The Cauvery River is the fourth-largest river in India, 
spanning four states and covering a total area of 81,155 km2. It has several 
tributaries and is a significant freshwater resource, harbouring a vast 
diversity of South Indian freshwater fish that support inland fisheries. The 
Vaigai River is another important river basin that flows through five 
districts of Tamil Nadu, spanning a length of 258 km. It supports the inland 
fisheries of the southern part of the state. In total, we surveyed 41 sites in 
the Cauvery (21 sites) and Vaigai (20 sites) river basins, covering four 
districts of Tamil Nadu—Tiruchirappalli, Thanjavur, Madurai, and Theni—
between April 2016 and March 2017. Based on their ecosystem type, the 
sites were classified as either lotic (characterised by flowing waters, such as 
rivers) or lentic (characterised by still waters, such as lakes). In the CRB, the 
lentic ecosystems include the Upper Anicut, the Grand Anicut, the Lower 
Anicut, and a few others; the Cauvery River, Kudamurutti River, Kollidam 
River, and others were classified as lotic ecosystems. Due to the lack of 
perennial water flow, a few sites generally classified as lotic were considered 
lentic ecosystems in the present study. For instance, Vadavar River sites 1 
and 2 were considered lentic ecosystems because there was no continuous 
water flow due to shortages in seasonal rainfall, poor water release from 
dams, habitat modifications, and water utilization. In the VRB, except the 
Vaigai River (lotic), we classified the remaining sites—Vaigai Dam, 
Vandiyur Lake, Valandur Lake, Sakkudi Lake, Odankundu Lake, 
Ananchiyur Lake, and Thenur Lake—as lentic ecosystems. 

In all the CRB and VRB study sites, the presence and absence of 
Pterygoplichthys spp. were recorded (sampling size, N = 48) along with the 
corresponding geographic coordinates in DMS (degrees, minutes, and 



[37] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

seconds) format using a GPS device (eTrex® 20x, Garmin). This data was 
converted to decimal degrees format, and the study site map (Figure 1) was 
created using QGIS software (version: 3.34.10-Prizren). The presence of 
Pterygoplichthys spp. was confirmed by fishing using cast nets (mesh size 
range: 10 mm2–50 mm2; weight: ~ 4 kg) and seine nets (mesh size range: 50 
mm2–90 mm2; weight: ~8 kg) with the help of local fishermen. Based on 
morphological keys, we identified the genus of this invasive fish species, 
and, based on abdominal patterns, identified the species (Armbruster and 
Page 2006; Wu et al. 2011; Bijukumar et al. 2015). However, for hybridized 
or intergrade populations of Pterygoplichthys species (such as P. pardalis and P. 
disjunctivus), species identification was found to be complex and inaccurate. 
Hence, the sailfin catfish group is uniformly referred to as the invasive fish 
species (IFS) Pterygoplichthys spp. throughout the study. Furthermore, we 
evaluated the physicochemical characteristics of the sites and the ecological 
and socio-economic impacts of the IFS in relation to comparator fish 
species (CFS). Here, CFS refers to the fish species group consisting of all 
native species and all commercially important fish species (including exotic 
taxa). Physicochemical characteristics, including pH, temperature, electrical 
conductivity, total dissolved solids (TDS), and salinity, were measured in 
the Pterygoplichthys spp. occurring sites using a handheld water quality tester 
(PCSTestr 35TM, Eutech Instruments) to understand their relationship with 
the population sustenance of the IFS and CFS. The unique habitats, land-
use activities, and nesting tunnels in the lotic and lentic ecosystems 
featuring Pterygoplichthys spp. were also recorded through in-field surveys and 
interviews with local people. 

2.2. Assessment of Ecological Impacts  

One important ecological impact of the Pterygoplichthys spp. invasion is the 
disruption of the CFS population in the inland water bodies of the CRB 
and VRB. Hence, we evaluated the abundance and biomass of the IFS in 
comparison to that of the CFS present in the fish harvest during the entire 
study period. The abundance was calculated by counting the number of IFS 
and CFS fish (species-wise) that were caught in each fish sampling. We 
estimated the biomass by separately measuring the total wet weight of the 
IFS and CFS (by species) caught in each sampling (Supplementary Figures 
S1 and S2). Then, we calculated the total abundance percentage and total 
biomass percentage to investigate the spread of the IFS compared to CFS 
in the surveyed sites. However, a few sites were excluded from the 
calculation due to inaccessibility resulting from a lack of water flow and 



Ecology, Economy and Society–the INSEE Journal [38] 

 

Figure 1. Overall Distribution Map of Pterygoplichthys spp. Along Several Inland Water Bodies of the Cauvery and Vaigai River Basins, Tamil Nadu.  

 

Source: Authors’ compilation 
Note: * and ** represent the sites that belong to the lentic and lotic ecosystem types, respectively. Sewage-contaminated study sites are 
formatted in italics. 

Identifiers: 

Cauvery River Basin: Upper 

Anicut* (A), Kambarasampettai 
Check Dam* (B), Kudamurutti River 
Site 1** (C), Cauvery River Site 1** 
(D), The Grand Anicut* (E), The 
Grand Anicut Canal Pit 1* (F), The 
Grand Anicut Canal Pit 2* (G), 
Cauvery River Site 2** (H), 
Kudamurutti River Site 2** (I), Vennar 
River Site 1** (J), Vennar River Site 
2** (K), Vettar River** (L), Vadavar 
River Site 1* (M), Vadavar River Site 2* 
(N), Kollidam River** (O), Lower 
Anicut Site 1* (P), Lower Anicut Site 
2* (Q), Lower Anicut Site 3* (R), 
Palavar River** (S), Nattar River** 
(T), and Arasalar River** (U). Vaigai 
River Basin: Vaigai Dam* (V), Vaigai 
River** (W), Vandiyur Lake* (X), 
Valandur Lake* (Y), and Sakkudi 
Lake* (Z) 



[39] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

other habitat modifications. From the overall sampling (N = 48) data, the 
relative occurrence (RO) of every CFS was calculated as the ratio of the 
number of individual samples of a particular CFS to the total number of 
samples. We measured the fecundity of Pterygoplichthys spp. by dissecting the 
ovaries of the gravid female fish captured during fish sampling. This was 
accomplished by counting a pre-weighed sub-sample of eggs in a sliced 
portion of the ovary. We then combined this data with the overall weight of 
the egg population to estimate the total number of eggs using the 
gravimetric method (Miller and Kendall 2009).  

2.3. Assessment of Socio-economic Impacts 

Pterygoplichthys spp. cause several socio-economic impacts in every ecosystem 
they invade. They can reduce CFS yields, affecting local communities’ 
revenue and protein intake. They can also make fish harvesting a strenuous, 
laborious, and tedious process and cause damage to fishing nets, leading 
fisherfolk to abandon their familial profession. These impacts are relatively 
unexplored. Hence, the socio-economic impacts of the Pterygoplichthys spp. 
invasion for common fishermen, lake leaseholders, and local people around 
the CRB and VRB were recorded using semi-structured interviews and case 
studies of mechanical IFS removal programmes. We conducted these semi-
structured interviews using a questionnaire that captured data on the 
livelihood-related impacts of the Pterygoplichthys spp. invasion. After 
obtaining informed consent, participants (N = 3) were randomly selected 
and individually interviewed in the regional language (Tamil) at each study 
site; we recorded the audio for documentation. The informed consent form 
and questionnaire for the semi-structured interview are given in the 
Supplementary Material. 

The mechanical removal programmes and the economic losses incurred by 
the fisherfolk were recorded at the Grand Anicut Canal Pits 1 and 2, and 
the Vandiyur Lake Pit, of the CRB and VRB during May 2016 and 
November 2016, respectively. The Grand Anicut Canal Pit 1 (10.7758°N, 
79.0227°E), with a dimension of 125×175×25 ft (l×b×d), and the Grand 
Anicut Canal Pit 2 (10.7528°N, 79.0498°E), with a dimension of 
125×175×15 ft, are located along the flow path of the Grand Anicut Canal 
(one of the tributaries of the Cauvery River), Thanjavur district, to aid water 
storage and aquaculture. These pits are massively infested with 
Pterygoplichthys spp., the stock population of which originated from the 
Grand Anicut and reached the pits through water releases.  

The Vandiyur Lake (9.9318°N, 78.1514°E) is a mesotrophic lake with a 
total surface area of 231.58 ha and a depth range of 2 m to 12 m. It is 
located in Madurai (suburban stretch) and is commercially used for 



Ecology, Economy and Society–the INSEE Journal [40] 

 

aquaculture. Due to seasonal effects, the available water is usually dispersed 
into several isolated water pits, which become infested by Pterygoplichthys 
spp. These fish proliferate throughout the lake once the water level returns 
to normal.  

Mechanical removal programmes are usually conducted before the CFS 
fingerling release season by leaseholders and fishing communities around 
the lakes, ponds, and canals invaded by Pterygoplichthys spp. to reduce 
competition from this invasive fish. We assessed the socio-economic 
impacts of Pterygoplichthys spp. removal programmes based on input–cost–
outcome parameters. Here, input refers to resources such as labour 
(fisherfolk), time (working days), and material (fishing net and equipment). 
Cost represents labour and equipment hiring charges as well as fishing net 
replacement charges. Outcome refers to the mass of invasive fish 
eliminated at the end of the programme. 

2.4. Statistical Analysis 

All the data formatting and descriptive statistics analysis were performed 
using Microsoft Excel 2021. We analysed site-level variations in the 
physicochemical characteristics of the invaded sites using the Kruskal-Wallis 
test. The statistical significance of the difference between the abundance 
and biomass of the IFS and CFS in both river basins was tested using the 
Wilcoxon rank-sum test, visualized through boxplots, and assessed using p-
values. Further, the degree of flow regulation; land-use activities, such as 
sewage disposal and cattle or cloth washing; the presence of invasive 
aquatic vegetation; and the existence of dams and bridges were assigned on 
a rank scale to the study sites (predictor variable) and compared against the 
IFS (biomass) percentage (response variable) through simple linear 
regression models. The effect of physicochemical parameter variations on 
the abundance and biomass of IFS and CFS was tested using Spearman’s 
rank correlation test, visualized through a multi-way correlation plot, and 
inferred through rs-values and p-values. To understand the site-level random 
effects of the physicochemical parameters and CFS abundance (CFSA) and 
biomass (CFSB) on the IFS abundance (IFSA) in both river basins, 
generalized linear mixed-effects models were developed. All data analysis 
and visualizations were performed using R software version 4.4.1 (RStudio 
Team 2025) with the following packages: “ggplot2”, “ggpubr”, “tidyverse”, 
“reshape2”, “patchwork”, and “glmmTMB”. 

 

 

 



[41] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

3. RESULTS 

This section describes i) the characteristics of the Pterygoplichthys spp. 
invaded sites; ii) ecological impacts with respect to CFSA and CFSB; iii) the 
relationship between the physicochemical characteristics and the abundance 
and biomass of IFS and CFS; and iv) the socio-economic impacts of the 
studied Pterygoplichthys spp. invasion. 

3.1. Habitat Characteristics 

During the study period, various land-use activities, including aquaculture, 
cattle washing, clothes washing, fishing, grazing, irrigation, sewage disposal, 
and others, were observed at the CRB and VRB sites (Table 1). Apart from 
regular water flow paths and open waters, certain unique habitats were 
predominantly occupied by IFS rather than CFS, and such instances varied 
by site. For instance, in the Kudamurutti River, Pterygoplichthys spp. were 
predominantly found in portions covered with invasive aquatic vegetation 
(Pontederia crassipes) and sewage-contaminated stretches of the river. In the 
Grand Anicut, Pterygoplichthys spp. were mostly found near the dam’s wall 
and shutters. In the Vennar River, Pterygoplichthys spp. were predominantly 
found in areas that contained abandoned break wall wreckage. 

Similarly, in the Vaigai Dam, Pterygoplichthys spp. were found in abundance in 
the rocky regions of the dam (Table 1). In comparison to the open waters 
of the Vaigai River, the stagnant water pools along the river, contaminated 
with domestic sewage, had a higher density of IFS than CFS. During the 
study period, we also identified IFS nesting tunnels along the banks of the 
sites. For instance, in the CRB, out of 21 sites, we observed nesting tunnels 
in three sites: Kudamurutti River, Vettar River, and Arasalar River. In the 
VRB, the Vaigai River and Vandiyur Lake had nesting tunnels (Table 1). 

Table 2 shows the physicochemical characteristics of the CRB and VRB 
sites invaded by Pterygoplichthys spp. In the CRB, all sites had an alkaline pH, 
with the highest pH value found in the Vettar River. The sites where 
domestic sewage was disposed of, such as the Kudamurutti River, had the 
highest conductivity, TDS, and salinity, followed by the Vadavar River and 
Arasalar River. However, we observed that the Upper Anicut had the 
lowest conductivity, TDS, and salinity. Likewise, in the VRB, the sewage-
contaminated Vandiyur Lake had the highest conductivity, TDS, and 
salinity. In contrast, Vaigai Dam had the lowest conductivity, TDS, and 
salinity (Table 2). However, the statistical analysis revealed that all the 
physicochemical parameters differ significantly (p < 0.01) across the 
Pterygoplichthys spp. invaded sites (Table 3). 



Ecology, Economy and Society–the INSEE Journal [42] 

 

Table 1. Habitat Characteristics of  Pterygoplichthys spp. Invaded Sites of  the Cauvery and Vaigai River Basins 

Habitat 
charac-
teristics 

Cauvery River Basin Vaigai River Basin 

Upper 
Anicut 

Kuda-
murutti 
River 

The 
Grand 
Anicut 

Vennar 
River 

Vettar 
River 

Vadavar 
River 

Arasalar 
River 

Vaigai 
Dam 

Vaigai 
River 

Vandiyur 
Lake 

Land-use 
activities 

Fishing, 
irrigation, 
and water 
storage 

Fishing and 
sewage 
disposal 

Fishing, 
irrigation, 
and water 
storage 

Fishing and 
cattle 

washing 

Fishing 
and 

cattle 
washing 

Fishing, 
grazing, 
cattle 

washing, 
and 

sewage 
disposal 

Fishing 
and 

sewage 
disposal 

Fishing, 
irrigation, 
and water 
storage 

Fishing, 
clothes 

washing, 
grazing, and 

sewage 
disposal 

Aqua-
culture, 
fishing, 

grazing, and 
sewage 
disposal 

Habitats 
predo-

minantly 
occupied 

Rocky 
regions 

Sewage-
conta-

minated and 
aquatic 

vegetation–
covered 
portions 

Regions 
near the 

dam’s wall 
and 

shutters 

Abandoned 
break wall 
wreckages 

Isolated 
water 
pools 
and 

aquatic 
vege-

tation–
covered 
portions 

Sewage-
conta-

minated 
and aquatic 
vegetation–

covered 
portions 

Sewage-
conta-

minated 
regions 

Rocky 
regions 

Sewage-
contaminated 
isolated water 

pools and 
aquatic 

vegetation–
covered 
portions 

Isolated 
water pools 
and aquatic 
vegetation–

covered 
portions 

Nesting 
tunnels 

along the 
banks 

Not 
recorded 

Recorded Not 
recorded 

Not 
recorded 

Recorded Not 
recorded 

Recorded Not 
recorded 

Recorded Recorded 

Source: Authors’ compilation  



[43] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

Table 2. Physicochemical Characteristics of  Pterygoplichthys spp. Invaded Sites of  the Cauvery and Vaigai River Basins 

Study 
Sites 

Cauvery River Basin Vaigai River Basin 

Upper 
Anicut 

Kuda-
murutti 
River 

The 
Grand 
Anicut 

Vennar 
River   

Vettar 
River 

Vadavar 
River 

Arasalar 
River 

Overall 
Value 

Vaigai 
Dam 

Vaigai 
River 

Vandiyur 
Lake 

Overall 
Value 

pH 
8.80 

(0.10) 
8.25 
(0.37) 

8.99 
(0.35) 

9.02 
(0.08) 

9.05 
(0.08) 

8.99 
(0.43) 

8.89  
(0.54) 

8.85 
(0.42) 

8.61 
(0.21) 

8.37 
(0.14) 

8.89  
(0.44) 

8.62 
(0.36) 

Temperature 
(°C) 

28.08 
(1.36) 

32.65 
(0.89) 

32.36 
(1.10) 

30.87 
(1.02) 

31.57 
(0.80) 

31.36 
(0.96) 

33.35 
(1.18) 

31.46 
(1.91) 

26.19 
(0.28) 

29.83 
(1.82) 

34.29 
(1.30) 

30.10 
(3.57) 

Conductivity 
(µS) 

727.50 
(14.05) 

1497.50 
(45.42) 

802.11 
(36.03) 

843.94 
(25.87) 

973.67 
(7.43) 

1215.61 
(175.95) 

1026.81 
(243.84) 

1012.45 
(274.22) 

260.22 
(5.10) 

1824.72 
(126.40) 

2326.67 
(216.81) 

1470.54 
(894.73) 

TDS     
(ppm) 

544.33 
(41.68) 

1057.96 
(36.54) 

573.39 
(15.35) 

598.94 
(10.03) 

694.00 
(8.77) 

833.18 
(129.55) 

738.93 
(158.81) 

720.10 
(185.29) 

185.11 
(4.69) 

1117.50 
(50.87) 

1647.78 
(154.73) 

983.46 
(613.87) 

Salinity   
(ppm) 

339.50 
(18.78) 

716.21 
(16.95) 

372.94 
(11.03) 

395.61 
(3.08) 

461.00 
(7.47) 

576.72 
(131.65) 

494.78 
(121.40) 

479.54 
(139.73) 

119.72 
(3.24) 

1012.94 
(192.76) 

1148.00 
(137.07) 

760.22 
(477.50) 

Source: Authors’ compilation 

Note: Values of  the water physicochemical parameters are given as Mean and Standard Deviation in parentheses. TDS: Total 
dissolved solids. 



Ecology, Economy and Society–the INSEE Journal [44] 

 

Table 3. Statistical Analysis of  Physicochemical Parameter Variations in the 
Pterygoplichthys spp. Invaded Sites of  the Cauvery and Vaigai River Basins Using the 
Kruskal-Wallis Test 

Physicochemical 
parameter 

Cauvery River Basin Vaigai River Basin 

p-value df H-value p-value df H-value 

pH 0.000** 6 125.52 0.000** 2 41.74 

Temperature (°C) 0.000** 204.47 0.000** 124.55 

Conductivity (µS) 0.000** 281.27 0.000** 125.86 

TDS (ppm) 0.000** 265.13 0.000** 127.12 

Salinity (ppm) 0.000** 270.81 0.000** 102.56 

Source: Authors’ analysis 

Note: ** denotes the significantly different p-values at 1% significance level. TDS: 
Total dissolved solids. 

3.2. Ecological Impacts 

As a whole, the total abundance of IFS across all CRB sites was significantly 
lower (p < 0.01) than that of the CFS (Figure 2A). However, the total 
biomass of IFS was significantly higher (p < 0.0001) (Figure 2B). Further, 
individual site-wise data revealed that sewage-contaminated lotic 
ecosystems, such as the Kudamurutti and Arasalar Rivers, had a 
significantly higher (p < 0.0001) total abundance of IFS compared to CFS 
(Figures 1 and 2A). Similarly, in lentic ecosystems, the aquatic vegetation–
covered and sewage-contaminated Vadavar River, followed by the Grand 
Anicut, were found to have a significantly higher (p < 0.0001) total 
abundance of IFS than CFS. However, the Upper Anicut (lentic ecosystem) 
had a significantly lower (p < 0.0001) total abundance of IFS than CFS; 
lotic ecosystems, such as the Vennar River and Vettar River, had a 
significantly higher (p < 0.0001) total abundance of CFS than IFS (Figures 1 
and 2A). The total biomass of IFS was significantly higher (p < 0.0001) in 
all lotic ecosystems except the Vennar River (Figures 1 and 2B). In lentic 
ecosystems, except Upper Anicut, the total biomass of IFS was significantly 
higher than that of CFS (Figures 1 and 2B). 

The total abundance and biomass of IFS were lower than those of CFS in 
the VRB when the sites were combined; however, the difference in biomass 
was non-significant (p > 0.05) (Figure 3A and B). From the individual site-
wise data, we found that the total abundance of CFS in the Vaigai River 
(lotic) was significantly higher (p < 0.001) than that of IFS (Figures 1 and 
3A).  



[45] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

Figure 2. Boxplot Representing the Individual and Total Sites’ Abundance (%) and Biomass (%) of Comparator Fish Species and 
Invasive Fish Species, Pterygoplichthys spp. in the Cauvery River Basin, with Statistical Analysis using Wilcoxon Rank-Sum Test. 
Abundance (A) and Biomass (B). 

Source: Authors’ analysis 
Note: ** and **** denote the significant difference at p < 0.01 and p < 0.0001, respectively.  



Ecology, Economy and Society–the INSEE Journal [46] 

 

Figure 3. Boxplot Representing the Individual and Total Sites’ Abundance (%) and Biomass (%) of Comparator Fish Species and 
Invasive Fish Species, Pterygoplichthys spp. in the Vaigai River Basin, with Statistical Analysis Using Wilcoxon Rank-Sum Test. 
Abundance (A) and Biomass (B). 

Source: Authors’ analysis 
Note: ***, ****, and ‘ns’ denote the significant difference at p < 0.001, p < 0.0001, and non-significant difference at p > 0.05, 
respectively. 



[47] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

Figure 4. Ecological Impact Assessment of Pterygoplichthys spp. in the Cauvery and 
Vaigai River Basins. Abundant Pterygoplichthys spp. Appeared in a Fish Catch at the 
Grand Anicut (A), Asian Needlefish at Vennar River (B), Pterygoplichthys spp. 
Individual at Vandiyur Lake (C), Nesting Tunnels of Pterygoplichthys spp. at Vettar 
River (D), Gravid Female Pterygoplichthys spp. Individual with Extruded Eggs at 
Vaigai River (E), and (F), Domestic Sewage Mixed Sites of Vadavar River (G), and 
a Large Population of Pterygoplichthys spp. Present in a Catch at Vadavar River (H) 

 

Source: Authors' compilation 



Ecology, Economy and Society–the INSEE Journal [48] 

 

In contrast, the total biomass of IFS was significantly higher (p < 0.0001) 
than that of CFS at the same site (Figures 1 and 3B). In lentic ecosystems 
such as Vaigai Dam, the total abundance of IFS was significantly lower (p < 
0.0001) than that of CFS. In contrast, the total biomass of IFS was 
significantly higher (p < 0.0001) than that of CFS at Vandiyur Lake, but 
lower at Vaigai Dam. Site-wise flow alterations (such as invasive aquatic 
vegetation domination) and human impacts (such as sewage disposal) had a 
statistically significant positive influence on the IFS’ biomass percentage in 
both the CRB (R2 = 0.79; p < 0.001) and VRB (R2 = 0.99; p < 0.001). 

In the CRB, CFS were recorded at sites where Pterygoplichthys spp. were 
present, such as the Grand Anicut (Figure 4A), the Kudamurutti River, the 
Upper Anicut, the Vennar River, and others. The species included Channa 
striata (snakehead murrel), Etroplus suratensis (pearlspot cichlid), 
Macrobrachium sp. (freshwater prawn), Xenentodon cancila (Asian needle fish) 
(Figure 4B), and so on (Table 4). In the overall sampling (N = 48), the RO 
of each CFS varied between the study sites. For instance, Mystus cavasius 
(Gangestic mystus) had the highest RO at the Vennar River, followed by 
the Vettar River and Vadavar River; the Kudamurutti River had the lowest 
RO of 10.42%. Among the CFS in all sites, Oreochromis niloticus (Nile tilapia) 
accounted for the highest RO at Upper Anicut. Furthermore, several CFS 
were present only in the CRB, and those particular study sites recorded 
minimal RO. For instance, Neolissochilus bovanicus (Bowany barb) at 
Kudamurutti River had an RO of 6.25% (Table 4). 

In the VRB, the recorded CFS included Channa punctata (spotted 
snakehead), Cirrhinus cirrhosus (mrigal carp), Mystus vittatus (striped dwarf 
catfish), and so on (Table 4). Similar to the CRB, the RO of the CFS varied 
across the VRB sites. For instance, Labeo rohita (rohu) had an RO of 45.83% 
at Vaigai Dam and 33.33% at Vandiyur Lake. O. niloticus in Vandiyur Lake 
had the highest RO among the CFS. In contrast, M. vittatus had the lowest 
RO compared to other CFS. Several CFS were present only in one of the 
VRB study sites with different levels of RO. For instance, C. cirrhosus was 
recorded only at Vaigai Dam with an RO of 64.48%. Some CFS, such as C. 
punctata, C. striata and Cyprinus carpio (common carp), were common to both 
the CRB and VRB. In contrast, CFS such as Catla catla (catla), Clarias 
gariepinus (North African catfish), and Heteropneustes fossilis (Asian stinging 
catfish) were present only in the VRB (Table 4). 

 

 



[49] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

Table 4. Relative Occurrence Percentage of Comparator Fish Species Recorded during the Sampling (N = 48) in the Cauvery and Vaigai 
River Basins 

Scientific 
name 

Common 
name 

Cauvery River Basin Vaigai River Basin 

Upper 
Anicut 

Kuda-
murutti 
River 

The 
Grand 
Anicut 

Vennar 
River 

Vettar 
River 

Vadavar 
River 

Arasalar 
River 

Vaigai 
Dam 

Vaigai 
River 

Vandiyur 
Lake 

Ambassis 
ambassis 

Commerson’s 
glassy 

- - - - 12.50 - - - - - 

Catla catla Catla - - - - - - - 33.33 - - 

Channa punctata Spotted 
snakehead 

- 20.83 - 18.75 - - - - 62.50 22.92 

Channa striata Snakehead 
murrel 

16.67 29.17 - - - - - 50.00 - - 

Cirrhinus cirrhosus Mrigal carp - - - - - - - 64.58 - - 

Cirrhinus reba Reba carp - 10.42 - 85.42 31.25 31.25 - - - - 

Clarias gariepinus North African 
catfish 

- - - - - - - 31.25 - - 

Cyprinus carpio Common carp 72.92 29.17 20.83 72.92 - - 45.83 - 31.25 - 

Etroplus suratensis Pearlspot cichlid 64.58 29.17 - - - - - - - - 

Glossogobius giuris Tank goby 16.67 14.58 20.83 18.75 - - - 41.67 - - 

Heteropneustes 
fossilis 

Asian stinging 
catfish 

- - - - - - - - - 18.75 

Hyporhamphus 
xanthopterus 

Red-tipped 
halfbeak 

- - - 10.42 - - - - - - 

Hypselobarbus 
jerdoni 

Jerdon’s carp - - - - - - - - 27.08 43.75 



Ecology, Economy and Society–the INSEE Journal [50] 

 

Labeo rohita Rohu - - 10.42 - - - - 45.83 - 33.33 

Macrobrachium 
sp. 

Freshwater 
prawn 

25.00 27.08 31.25 12.50 25.00 - - - - - 

Mastacembelus 
armatus 

Zig-zag eel 20.83 10.42 16.67 - - - - 18.75 - - 

Mystus cavasius Gangetic mystus - 10.42 - 83.33 22.92 22.92 - - - - 

Mystus vittatus Striped dwarf 
catfish 

35.42 22.92 - 52.08 20.83 27.08 50.00 - 47.92 12.50 

Neolissochilus 
bovanicus 

Bowany barb - 06.25 - - - - - - - - 

Ompok 
bimaculatus 

Butter catfish - 14.58 - - - - - 66.67 - - 

Oreochromis 
mossambicus 

Mozambique 
tilapia 

- - - 56.25 29.17 27.08 31.25 - - - 

Oreochromis 
niloticus 

Nile tilapia 95.83 47.92 12.50 - - - - 58.33 75.00 56.25 

Puntius sophore Pool barb - 08.33 - 18.75 31.25 31.25 14.58 - - - 

Trichogaster lalius Dwarf gourami - 08.33 - 12.50 - - - - - 54.17 

Wallago attu Helicopter 
catfish 

- - - - - - - 20.83 - - 

Xenentodon 
cancila 

Asian needlefish 16.67 06.25 - 37.50 - - - - - - 

Source: Authors’ analysis 

Note: ‘-’ denotes the non-occurrence of  the species in the respective study site 

 



[51] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

During the study period, horizontal nesting tunnels of Pterygoplichthys spp. 
(Figure 4C) were observed along the banks of lotic sites such as the 
Kudamurutti River, Vettar River (Figure 4D), and Arasalar River in the 
CRB, followed by Vaigai River and Vandiyur Lake in the VRB. We 
calculated the fecundity of the gravid female Pterygoplichthys spp. individuals 
(Figure 4E and F) in the sample and found 7543.66 ± 688.72 eggs. The sites 
where domestic sewage water had mixed into the water bodies, including 
the Vaigai River and Vandiyur Lake of the VRB, as well as the Kudamurutti 
River, Arasalar River, and Vadavar River (Figure 4G) of the CRB, had an 
abundant population of IFS (Figure 4H). 

3.3. Physicochemical Parameters’ Effect 

We performed Spearman’s rank correlation analysis to determine the effects 
of physicochemical parameter variations on the abundance and biomass of 
invasive Pterygoplichthys spp. (IFSA and IFSB) and comparator fish species 
(CFSA and CFSB). The multi-way correlation plots are shown in Figure 5A 
and B. In the CRB, pH exhibited a statistically significant, albeit weak, 
negative correlation with IFSA and IFSB (Figure 5A). We observed a 
similar relationship with CFSA and CFSB. However, temperature had a 
negligible correlation with IFSA and a weak but statistically significant 
positive correlation with IFSB. In contrast, temperature exhibited a 
moderate yet significant negative correlation with CFSA and CFSB (Figure 
5A). The correlation coefficients of other physicochemical parameters, such 
as conductivity, TDS, and salinity, exhibited a statistically significant, albeit 
weak, negative correlation with the total abundance and biomass of CFS. In 
contrast, conductivity had a non-significant correlation, TDS had a 
significant but weak positive correlation, and salinity had a negligible 
correlation with IFSA. Yet, conductivity, TDS, and salinity exhibited a 
significant, albeit weak, positive correlation with the IFSB (Figure 5A). All 
the statistical differences were significant at the p < 0.05 level. 

In the VRB, pH had a statistically negligible correlation with IFSA and 
IFSB, as well as with CFSA and CFSB (Figure 5B). However, temperature 
and conductivity were found to have a weak negative correlation to IFSA 
and IFSB. On the contrary, the same parameters had a strong negative 
correlation with CFSA and CFSB, respectively. TDS had a moderate 
negative correlation with IFSA and a weak positive correlation with IFSB. 
In contrast, TDS had a strong negative correlation with CFSA and CFSB. 
The correlation coefficients of salinity showed a strong negative correlation 
with CFSA and CFSB, whereas there was a weak negative correlation and a 
moderate positive correlation with IFSA and IFSB, respectively. However, 
except for pH (p > 0.05), all the other physicochemical parameters had a 



Ecology, Economy and Society–the INSEE Journal [52] 

 

statistically significant relationship between the abundance and biomass of 
CFS and IFS at the level p < 0.05 (Figure 5B). 

Figure 5. Spearman’s Rank Correlation Coefficients between Physicochemical 
Parameters and Abundance and Biomass of Comparator Fish Species and Invasive 
Pterygoplichthys spp. at Cauvery River Basin (A) and Vaigai River Basin (B) 

 

Source: Authors’ compilation 

Note: Values in the marked cells denote the correlation coefficients rs having a p-
value > 0.05 (non-significant). Temp: temperature; Cond: conductivity; TDS: total 
dissolved solids; Sal: salinity; CFSA: comparator fish species’ abundance; CFSB: 
comparator fish species’ biomass; IFSA: invasive fish species’ abundance; and 
IFSB: invasive fish species’ biomass. 

3.4. Generalized Linear Mixed Models with Site-level Random 
Effects 

Generalized linear mixed models (GLMMs) were developed by recursively 
adding and removing physicochemical parameters and CFSA and CFSB as 
fixed effects, with IFSA as the response variable, while accounting for study 
site–level variations (i.e., random effects). The models used the maximum 
likelihood estimation method, and the likelihood of random effects on the 
GLMMs was approximated using the Laplace approximation method. 
Through the recursive approach, the final model was developed based on 
improved comparative statistics, including Akaike Information Criterion 
and Bayesian Information Criterion values, as well as the statistical 
significance (p-value) of the independent variables. In the GLMM of the 



[53] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

CRB, among the physicochemical parameters, salinity showed a statistically 
non-significant (p > 0.05) positive association with IFSA with a statistically 
significant (p < 0.05) intercept. CFSA had a statistically significant (p < 0.01) 
negative association, and CFSB had a highly significant (p < 0.001) positive 
association with IFSA (Table 5). On the other hand, in the GLMM of the 
VRB, TDS had a statistically significant (p < 0.001) negative association 
with IFSA with a statistically significant intercept (Table 5). 

Table 5. Generalized Linear Mixed Model with Site-Level Random Effects to 
Determine the Relationship between Physicochemical Parameters, the Abundance 
and Biomass of Comparator Fish Species, and Invasive Pterygoplichthys spp. 
Abundance 

GLMM 
characteristics 

Cauvery River Basin Vaigai River Basin 

Comparative statistics 

Akaike information 
criterion (AIC) 

3219.00 1383.60 

Bayesian information 
criterion (BIC) 

3241.90 1398.50 

Log-likelihood –1603.50 –686.80 

Parameter estimates Fixed 
effects 

p-value Fixed 
effects 

p-value 

Intercepts 34.8578 0.0120* 55.6080 0.0000*** 

Total dissolved solids - - –0.0220 0.0007*** 

Salinity 0.0039 0.8550 - - 

CFSA –0.0384 0.0036** 0.0027 0.4109 

CFSB 3.7857 0.0000*** - - 

Source: Authors’ analysis 
Note: *, **, and *** denote the significantly different p-values at the 5%, 1%, and 
0.1% significance levels, respectively. CFSA: comparator fish species’ abundance; 
CFSB: comparator fish species’ biomass. 

3.5. Socio-economic Impacts 

In addition to the ecological impacts, the invasion of Pterygoplichthys spp. in 
parts of the CRB and VRB has adversely affected the livelihoods of fishing 
communities. This section describes the most common IFS-related 
livelihood problems faced by fishing communities, as reported during our 
semi-structured interviews and case studies of mechanical removal 
programmes. Since Pterygoplichthys spp. have widely occupied fishing habitats 
along the CRB and VRB, nearly all the interviewees noted that these 
invasive fish were trapped in fishing nets almost every time they fished 
(Figure 6A). The spiny nature of this fish causes it to become heavily 
entangled in fishing nets, requiring considerable time and effort to remove 
it without damaging the net (Figure 6B). During the removal process, 



Ecology, Economy and Society–the INSEE Journal [54] 

 

fishermen’s palms often get scratched and bleed. The fishermen also 
emphasised that they often had to cut off portions or discard fishing nets 
that were entangled with these fish. This reduced the durability and usage of 
fishing nets, ultimately forcing fisherfolk to purchase new nets, which 
caused additional economic distress. The time-consuming removal process 
also resulted in fisherfolk returning late to the selling point with their poor 
CFS yields, resulting in a low income and ultimately diminishing their 
livelihoods. 

The interviewed fishermen also explained that they routinely made 
additional efforts to capture IFS to minimize their population. Lacking 
alternatives, fishermen discard the IFS in nearby areas or landfills. These 
disposals create a foul smell, resulting in an uncomfortable and nauseating 
environment for the local population. The interviewees also revealed that 
some members of fishing communities, which had been fishing for several 
generations, had to quit and take up daily wage jobs, such as painting or 
civil work. With no other options available, only older fishermen and those 
who had made fishing their profession continued fishing. According to a 
few of them, the daily and annual income they could earn from fishing had 
reduced threefold following the invasion of tank cleaner fish. The 
fishermen, dependent solely on fishing, highlighted their reduced protein 
intake due to poor CFS yields. 

Similarly, leaseholders involved in aquaculture reported that their revenue 
losses were mainly due to increased expenditure on labour for removing 
IFS. However, their efforts were unsuccessful, as even a small population of 
IFS, owing to their high fecundity rate, could generate a large population in 
a few months by consuming the food supplied for the CFS. This, in turn, 
led to reduced resources for CFS, resulting in poor abundance and biomass, 
which eventually led to lower market value. Given these circumstances, 
people were unwilling to lease the sailfin catfish–infested lakes and ponds, 
leading to unemployment for many dependent fishermen. The problems 
encountered by these fishing communities were not accurately reported to 
the concerned governing bodies. Overall, the Pterygoplichthys spp. invasion 
had adversely affected the livelihoods of thousands of fisherfolk. 

As discussed in the methodology, this study also examined the socio-
economic impacts on leaseholders and fishermen arising from the need to 
implement mechanical removal programmes. We analysed removal 
programmes at the Grand Anicut Canal Pits 1 and 2 and Vandiyur Lake Pit 
using the input–cost–outcome associated parameters (Table 6 and Figure 
6C–G). Before releasing commercial fish fingerlings for aquaculture, 
leaseholders conduct mechanical removal programmes. We analysed these 



[55] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

programmes through i) the resource inputs in terms of labour, time, and 
materials, ii) the associated costs, and iii) the resulting outcomes of the IFS 
removal. During the programme at the Grand Anicut Canal Pits 1 and 2, 
the efforts of 22 workers over seven days, using seven fishing nets, incurred 

a total expenditure of ₹1,16,900 and resulted in the removal of five tonnes 
of IFS (Table 6). Though a significant proportion of the IFS in the pits was 
removed, the pits became infested with IFS again following water release 
from the Grand Anicut. Hence, the mechanical removal programme 
resulted in a considerable loss for the leaseholders. 

Table 6. Overall Resource Inputs, Associated Costs, and the Resulting Outcomes 
of the Mechanical Removal Programmes of Pterygoplichthys spp. in the Grand Anicut 
Canal Pits 1 and 2 and Vandiyur Lake Pit 

Field site The Grand 
Anicut 

Canal Pit 1 

The Grand 
Anicut 

Canal Pit 2 

Vandiyur 
Lake Pit 

Input 

No. of labourers hired 10 12 15 

No. of working days 7 7 1 

No. of fishing nets (size) 3 (10 mm) 4 (10 mm) 2 (10 mm) 

Equipment hired - - Water 
suction 
pump 

Cost 

Individual labour charges/day (in 
INR) 

600 600 550 

Total labour charges (in INR) 42,000 50,400 8,250 

Equipment hiring charges/day (in 
INR) 

- - 1,000 

Total cost of fishing net (in INR) 10,500 14,000 7,000 

Total expenditure (in INR) 52,500 64,400 16,250 

Outcome 

Total biomass of Pterygoplichthys spp. 
eliminated (in kg) 

1,500 3,500 300 

Source: Authors’ compilation 

  



Ecology, Economy and Society–the INSEE Journal [56] 

 

Figure 6. Assessment of the Socio-economic Impacts of the Pterygoplichthys spp. 
Invasion in the Cauvery and Vaigai River Basins: (A) Fisherman Showing a Large 
Number of Pterygoplichthys spp. Trapped in the Fishing Net, (B) Complexly 
Entangled Sailfin Catfish, (C) Fishermen Involved in the Mechanical Removal of 
Invasive Sailfin Catfish at the Grand Anicut Canal Pit 1, (D) and (E) Huge 
Population of Pterygoplichthys spp. Removed During the Programme, (F) Fishermen 
Discarding the Trapped Fishing Net at the Grand Anicut Canal Pit 2, and (G) 
Preventing Fish from Entering the Suction Hose during the Mechanical Removal 
Programme at Vandiyur Lake Pit. 

 

Source: Authors’ compilation 



[57] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

Similarly, at Vandiyur Lake, the leaseholder employed 15 fishermen for the 
mechanical removal programme and provided them with wages and food. 
The fishermen identified a pit with minimal water and a large number of 
IFS along with a sparse population of CFS. They used a water suction 
pump to remove the water, placing a net in front of the suction hose to 
prevent fish from entering it (Figure 6G). The IFS were discarded on 
nearby land. The fishermen also collected juvenile CFS, such as Nile tilapia 
(Oreochromis niloticus), Asian stinging catfish (Heteropneustes fossilis), and 
spotted snakehead catfish (Channa punctata). The mechanical removal 
programme took place over one day, incurred a total expenditure of 

approximately ₹16,250, and resulted in the removal of 300 kg of 
Pterygoplichthys spp. (Table 6). However, the fishermen were unable to 
remove the entire population of Pterygoplichthys spp., as a few juveniles were 
partially buried in the mud, and several pits were still infested with 
Pterygoplichthys spp. This outcome significantly distressed the workers and 
the leaseholder, leading to the suspension of the removal programme. 

 

4. DISCUSSION 

Pterygoplichthys spp. can occupy various habitats, including cool to warm 
water and fast- to slow-flowing streams. They can survive in oxygen-rich 
water and stagnant pools and live in a broad range of water conditions, 
from acidic to alkaline (Mendoza et al. 2009). In the present study, the 
Pterygoplichthys spp. were mostly found in alkaline water conditions in both 
the CRB and VRB. Similar to the results found in Nico and Martin (2001) 
and Chavez et al. (2006), the Pterygoplichthys spp. populations recorded in the 
present study were able to tolerate low water quality. They were 
predominantly found in sewage-contaminated sites such as the 
Kudamurutti River, Vadavar River, and Arasalar River of the CRB, as well 
as the Vaigai River and Vandiyur Lake of the VRB. The correlation analysis 
revealed that these sewage-contaminated sites have higher values of 
conductivity, TDS, and salinity; however, they showed weak to moderate 
correlations with the abundance and biomass of invasive Pterygoplichthys spp. 
Although these water quality parameters may not have a direct effect, they 
lead to algal blooms (Ayele and Atlabachew 2021), which serve as a food 
resource for tank cleaner fishes.  

In addition, we found that the sewage-contaminated sites were dominated 
by invasive Pontederia crassipes (formerly Eichhornia crassipes - water hyacinth), 
native to South America, which helps support a sustainable population of 
Pterygoplichthys spp. The dense mat of P. crassipes provided a predator-free 
environment for the juveniles of Pterygoplichthys spp. (Tran et al. 2021). It also 



Ecology, Economy and Society–the INSEE Journal [58] 

 

provided a healthy breeding site for the adults (Hussan et al. 2019) by 
increasing phytoplankton densities and supporting detritus accumulation 
under their bushy root structure (Tran et al. 2021). These conditions ensure 
a reliable food supply for the IFS. From this, we can infer that the 
beneficial association between the two worst invasive species (Pterygoplichthys 
spp. and P. crassipes) is evident in their wide dispersal (Tran et al. 2021) in the 
inland water bodies of the CRB and VRB. Furthermore, the continuous 
discharge of sewage water at these sites during drought conditions 
ultimately supports these IFS populations throughout the year.  

Similar to the findings of Wang et al. (2021) and Monico et al. (2022), we 
found that alterations in the flow regimes of inland water bodies, through 
the construction of dams and bridges; the spread of invasive aquatic 
vegetation such as P. crassipes; and anthropogenic disturbances such as 
sewage disposal, favours the sustenance of IFS over CFS. However, there 
were a few study sites in both the river basins, including the 
Kambarasampettai Check Dam, Cauvery River Sites 1 and 2, Palavar River, 
Nattar River, Valandur Lake, and Sakkudi Lake, where there was no stable 
maintenance population of either CFS or IFS due to irregular water 
availability resulting from both natural and anthropogenic activities. One 
possible reason for this discontinuous water availability is the poor 2016 
north-eastern monsoons in Tamil Nadu, particularly, in the districts where 
the Cauvery and Vaigai rivers faced deficient (–20% to –59%) to significant 
deficient rainfall (–60% to –99%) compared to the average rainfall 
(Balachandran 2016). 

Disruption of the aquatic food chain, reduction in the abundance of native 
organisms, mortality of shorebirds, changes in aquatic plant populations, 
and bank erosion were some of the reported ecological consequences of the 
Pterygoplichthys spp. invasion (Orfinger and Gooding 2018). For instance, P. 
multiradiatus has been linked to a decline in carp and tilapia fisheries, as well 
as damage to fishing gear, in El Infiernillo Reservoir, Mexico (Rueda-Jasso 
et al. 2013). Similarly, in the present study, due to the presence of IFS in the 
CRB and VRB, the abundance and biomass of CFS such as Xenentodon 
cancila (Asian needlefish), Cirrhinus cirrhosus (Mrigal carp), Channa striata 
(snakehead murrel), and Glossogobius giuris (tank goby) were observed to be 
reduced in fish catches in several study sites. Nevertheless, in the lotic 
ecosystems of the CRB, the total abundance of CFS was higher than that of 
IFS, mainly due to the presence of Mystus cavasius (Gangetic mystus, 
weighing less than 10 g) in the fish catches made in the Vennar River. In 
the VRB, the total CFSA was higher primarily due to the use of several sites 
for commercial aquaculture, where several thousand CFS fingerlings are 
released each year. Other than Vaigai Dam, CFSB was lower than IFSB in 



[59] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

the VRB due to the occurrence of abnormally large IFS individuals. The 
IFS compete for food and living space, resulting in a lower yield of CFS 
compared to previous years. 

Pterygoplichthys spp. reproduce via sexual reproduction and throughout the 
year with a high fecundity rate. On average, a single female individual in a 
spawning season can lay between 3,600 and 6,900 eggs, with the number 
varying by size and species (Gibbs et al. 2008). In the natural drainages of 
Thiruvananthapuram, Kerala, Raj et al. (2021) reported the absolute 
fecundity of different-sized individuals of P. pardalis to be in the range of 
923–14,777 eggs. However, in the present study, up to 7,500 eggs were 
recorded for the gravid female Pterygoplichthys spp. individuals caught in the 
study sites. This higher fecundity can be attributed to the absence of natural 
enemies and the increased availability of food resources due to algal blooms 
in sewage-contaminated sites. Seasonal effects also influence the fecundity 
of Pterygoplichthys spp. (Gibbs et al. 2017). In this species, an interesting 
parental behaviour exists, where male individuals construct horizontal 
burrows 30–140 cm deep along the banks of rivers, lakes, and ponds that 
serve as nesting tunnels for females to lay eggs (Lienart et al. 2013). Once 
the eggs have been laid, the males guard the eggs until they hatch, releasing 
larvae (Mendoza et al. 2009). In the present study, we observed horizontal 
nesting tunnels along the banks at water-depleted portions of the study 
sites, including the Kudamurutti River, Vettar River, Arasalar River, Vaigai 
River, and Vandiyur Lake. Such burrows have previously been reported to 
weaken the bank structure, ultimately leading to siltation problems in 
several invaded regions, including Hawaii and Florida (Nico et al. 2009). 

The sociological problems faced by fishing communities due to the 
Pterygoplichthys spp. invasion extends beyond economic losses; it is a life-or-
death situation. Drawing a net full of Pterygoplichthys spp. rather than CFS 
has a severe psychological impact on fishermen. Besides the damage to 
fishing gear (Global Invasive Species Database 2025), the laborious process 
of removing spiny Pterygoplichthys spp. often injures the fishermen’s hands 
and delays the effective fishing of CFS, subsequently impacting the time at 
which the poor yields of CFS are sold. This severely affects their daily 
incomes and poses significant constraints on the day-to-day lives of fishing 
communities. These situations have even prompted fishermen to abandon 
their familial profession for employment in other sectors. However, the 
unskilled average fisherfolk who depend on fishing to meet their protein 
needs have no alternative. 

The mechanical removal programmes reported in this study offer deep 
insights into the socio-economic impact of the Pterygoplichthys spp. invasion. 



Ecology, Economy and Society–the INSEE Journal [60] 

 

Mechanical removal programmes are generally considered the preferred 
control method due to the problems associated with non-specific chemical 
control methods and biocontrol methods, which can introduce new exotic 
organisms (Messing and Wright 2006). Furthermore, mechanical removal 
programmes require a significant amount of manpower and money to cover 
wages, food, damage to fishing equipment, and other additional expenses. 
In this study, mechanical removal programmes could only partially remove 
the Pterygoplichthys spp., as subsequent water releases from the associated 
dams and monsoon rainfall led to the proliferation of Pterygoplichthys spp. 
again. An important point to note here is that the cost of mechanical 

removal was approximately ₹1,50,000 for just a few days of work at each 
pit. Hence, the total expenditure required to completely remove 
Pterygoplichthys spp. from the CRB and VRB would be staggering. 

The present study attempted to describe the ecological and socio-economic 
impacts of the Pterygoplichthys spp. invasion in major inland water bodies in 
the Cauvery and Vaigai River Basins. The findings underscore the urgent 
need to increase awareness among ecologists, academics, politicians, 
policymakers, and the general public regarding the seriousness of the issue. 
Further, it emphasizes the need to develop novel or alternative management 
strategies to curb the invasion of Pterygoplichthys spp. and similar exotic pets 
in Indian ecosystems. Additionally, promoting native ornamental freshwater 
and marine fish, as well as other small pet animals for aquariums and 
petting purposes, through extensive outreach programmes targeting 
younger and older generations can aid in the prevention of future invasion 
episodes. 

 

5. CONCLUSION 

Based on this study, the following conclusions can be drawn: i) the biomass 
of IFS is comparatively higher than that of CFS at most sites in the Cauvery 
and Vaigai river basins; ii) mechanical control measures undertaken by the 
fishing communities for the removal of invasive Pterygoplichthys spp. are not 
effective; iii) strict regulations are required to monitor the transactions of 
sellers, buyers, and keepers of exotic pets or aquarium species; and iv) 
innovative management and control strategies are needed to eradicate 
invasive Pterygoplichthys spp. 

 

Supplementary Material: The site-wise specifics of the abundance (nos.) 
and biomass (kg) of IFS and CFS in the CRB and VRB are detailed in 
Supplementary Figures S1 and S2. The informed consent form and 



[61] Rajasekaran, Ravichandran, Balasingam, and Sivagnanam  

 

questionnaire used for the semi-structured interview to record the socio-
economic impacts on fishing communities are provided in the 
Supplementary Material. 

ACKNOWLEDGEMENTS 

We thank the fishing communities of the Cauvery and Vaigai river basins 
for their help and support in collecting the field data for this research study. 
We acknowledge the anonymous reviewers and copyeditor for their 
valuable comments and suggestions, which helped improve the quality of 
the manuscript.  

Author contributions: MRR and CS conceptualized and designed the 
study; MRR, ISR, and PB performed field data collection; MRR and ISR 
analysed the data; PB and MRR prepared the study site map; MRR wrote 
the first draft of the original manuscript; MRR and CS revised the 
manuscript; CS supervised the entire study. All authors read and approved 
the final manuscript. 

Funding: This study was financially supported by Tamil Nadu State Land 
Use Research Board (TNSLURB), State Planning Commission, Tamil Nadu 
(Ref. No. 535/SPC/LUD/2016), UGC-STRIDE Programme (Ref. No. 
F.29/2019 (STRIDE-I)), University Grants Commission, New Delhi, and 
Rashtriya Uchchatar Shiksha Abhiyan (RUSA)-MKU. 

Data availability statement: The data generated and analysed during the 
current study are available from the first author and the corresponding 
author upon reasonable request. 

Conflict of interest statement: The authors declare no conflict of interest. 

Consent for publication: Not applicable. 

Ethics approval: Not applicable. 

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https://doi.org/10.1894/0038-4909(2007)52%5b141:ASCPPC%5d2.0.CO;2
https://doi.org/10.1111/ddi.13376
https://doi.org/10.1016/j.japb.2024.01.015


Ecology, Economy and Society–the INSEE Journal 8(2): 33-66, July 2025  

RESEARCH PAPER (Supplementary material) 

The Ecological and Socio-economic Impacts of the 
Aquarium Sailfin Catfish Invasion: Fate of Fisherfolk 
at Major Inland Water Bodies, Tamil Nadu, South 
India  
Mohan Raj Rajasekaran, Indhar Saidanyan Ravichandran, Parthiban 

Balasingam, and Chandrasekaran Sivagnanam 

Abstract: Keeping pets has been part of human life since the earliest civilizations. 
Today, exotic animals are sold online and shipped globally to enthusiasts. However, 
pet sellers and keepers sometimes release exotic pets into nearby natural 
ecosystems, leading to biological invasion. This paper examines the invasion by 
sailfin catfish (Pterygoplichthys spp.) of Cauvery and Vaigai river basins, and its 
ecological and socio-economic impacts. We assessed the ecological impacts by 
comparing the total abundance and biomass of the invasive fish species (IFS), 
Pterygoplichthys spp., with those of comparator fish species (CFS) and various 
physicochemical parameters. We used semi-structured interviews and case studies 
of IFS mechanical removal programmes to assess the socio-economic impacts. The 
abundance and biomass of the IFS were significantly higher than those of the CFS 
in most lentic and lotic ecosystems. Interviews revealed significant sociological 
impacts on fisherfolk, including a push from fishing (a familial profession) to non-
fishing vocations. The input–cost–outcome assessment of mechanical removal 
programmes revealed that the expenditure incurred could not prevent further 
invasion of the IFS. This study advocates for increasing awareness among 
stakeholders to devise effective control measures and implement policy-level 
changes to curb the sailfin catfish invasion in India’s inland water bodies. 

Keywords: Pterygoplichthys spp., Biological Invasion, Ecological and Socio-economic 
Impacts, Fishing Communities, Cauvery River Basin, Vaigai River Basin. 

 

 Department of Plant Sciences (DPSc), School of Biological Sciences (SBS), Madurai 
Kamaraj University, Madurai - 625021, India (MKU); santhamoorthy92@gmail.com  

 DPSc, SBS, MKU; saidanyan@gmail.com  

 DPSc, SBS, MKU; parthibanpana@gmail.com 

 DPSc, SBS, MKU; csekaran.biological@mkuniversity.ac.in.  

Copyright © Rajasekaran, Ravichandran, Balasingam, and Sivagnanam 2025. Released under 
Creative Commons Attribution © NonCommercial 4.0 International licence (CC BY-NC 

4.0) by the authors.  

Published by Indian Society for Ecological Economics (INSEE), c/o Institute of Economic 
Growth, University Enclave, North Campus, Delhi 110007.  

ISSN: 2581–6152 (print); 2581–6101 (web).  

DOI:  https://doi.org/10.37773/ees.v8i2.1191  

mailto:santhamoorthy92@gmail.com
mailto:saidanyan@gmail.com
mailto:parthibanpana@gmail.com
mailto:csekaran.biological@mkuniversity.ac.in
https://doi.org/10.37773/ees.v8i2.1191


Ecology, Economy and Society–the INSEE Journal  

Figure S1. Boxplot Representing the Individual and Total Sites’ Abundance (No.) and Biomass (kg) of Comparator Fish Species and 
Invasive Fish Species, Pterygoplichthys spp. in the Cauvery River Basin and with Statistical Analysis Using Wilcoxon Rank-Sum Test. 
Abundance (A) and Biomass (B). 

 

Source: Authors’ analysis 

Note: **, ****, and ‘ns’ denote the significant difference at p < 0.01, p < 0.0001, and non-significant difference at p > 0.05, respectively. 



Rajasekaran, Ravichandran, Balasingam, and Sivagnanam 

Figure S2. Boxplot Representing the Individual Site’s and Total Sites’ Abundance (No.) and Biomass (kg) of Comparator Fish Species 
and Invasive Fish Species, Pterygoplichthys spp. in the Vaigai River Basin and with Statistical Analysis Using Wilcoxon Rank-Sum Test. 
Abundance (A) and Biomass (B). 

 

Source: Authors’ analysis 

Note: ***, ****, and ‘ns’ denote the significant difference at p < 0.001, p < 0.0001, and non-significant difference at p > 0.05, 
respectively



Ecology, Economy and Society–the INSEE Journal  

Informed Consent Form for the Semi-Structured Interview 

Project Title: Studies on the Ecological, Economical, and Sociological Impacts of 
Invasive Species in Tamil Nadu 

Funding Agency: Tamil Nadu State Land Use Research Board (TNSLURB), State 
Planning Commission, Tamil Nadu (Ref. No. 535/SPC/LUD/2016) 

Project Context: To study the various problems caused by invasive species, 
particularly Pterygoplichthys spp. (hereafter tank cleaner fish), in relation to the natural 
ecosystem and the local people in the Cauvery and Vaigai river basins  

Conditions: 

I agree to participate in this project through this interview with the following 
conditions: 

• The project studies the ecological, economic, and sociological impacts of 
invasive species in Tamil Nadu. For this purpose, semi-structured 
interviews will be conducted with key informants (leaseholders of a 
particular water body, fishermen, local people, etc.). 

• Interviews will last for about one hour, and questions will deal with the 
ecological, sociological, and economic problems encountered by the 
people in the study area due to invasive species. 

• The interview I give and the information it contains will be used solely for 
the purposes defined by the project. 

• At any time, I can refuse to answer certain questions, discuss certain 
topics, or even put an end to the interview without prejudice to myself. 

• To facilitate the interviewer’s job, the interview can be recorded. 
However, the recording will be deleted as soon as it has been transcribed. 

• All interview data will be handled carefully to protect the interviewees’ 
confidentiality. Therefore, no names will be mentioned, and the 
information will be coded. 

For any information about the project, contact Prof. S. Chandrasekaran, 
Principal Investigator (TNSLURB Project), Head, Department of Plant Sciences, 
School of Biological Sciences, Madurai Kamaraj University, Madurai 625021. 

 

Respondent’s signature    Interviewer’s signature 

 



Rajasekaran, Ravichandran, Balasingam, and Sivagnanam 

Semi-Structured Interview Questionnaire 

i) Introduction 

1. Introduction of the Interviewer  

2. Purpose of the Interview 

3. Introduction of the Interviewee (asking the following details) 

Name: 

Native place: 

Occupation: 

How long have they been working in the fishing profession? 

ii) Main Portion of the Interview 

Focusing Theme: Economic and Sociological Impacts of Pterygoplichthys spp. in 
Cauvery and Vaigai River Basin 

1. When did you notice the tank cleaner fish for the first time in this area? 

2. How did it occur? 

3. When did the tank cleaner fish first start troubling you? What are the 
problems with it? 

4. What are all the fish species affected by the tank cleaner fish? How are 
they affected by it? 

5. Which portion of the water body has the highest population of tank 
cleaner fish? 

6. Comparatively, which year/month has the highest recorded number of 
tank cleaner fish in the catch? 

7. Has it reduced or increased after it was caught to the maximum? 

8. At what time are the tank cleaner fish active? 

9. Have there been any changes in the water quality of the water body due to 
tank cleaner fish invasion? 

10. Have there been any damages caused to your fishing equipment? 

11. Did this fish invasion affect your decision to take a lease of a particular 
lake/pond?  

12. Did this fish invasion require more labour, work, and money to eliminate 
the fish in the leased water body? 

13. How much did you spend on eliminating this fish from the leased water 
body at one time? How many times did you attempt to eliminate this fish? 



Ecology, Economy and Society–the INSEE Journal 

14. Is your total annual income affected by the tank cleaner fish invasion? 

15.  Is anyone interested in buying this fish? For what purpose do they buy it? 

16. At what size and for what price are they buying the fish? 

17. How often do they buy the tank cleaner fish? 

18. Have you made a profit from this fish? Did you gain any valuable amount 
from this fish? 

19. Is anyone or any farm nearby cultivating this fish? 

20. Has this fish invasion affected your time spent catching comparator fish 
species? 

21. Did this fish invasion make you stressed and quit based on the poor yield 
of valuable comparator fish species? 

22. Has this fish invasion affected your food demand or daily family income 
generated from selling the comparator fish? 

23. Have you eaten this fish? How do you prepare it? 

24. Has this situation led you to quit fishing and search for an alternative? 

25. Does the new job provide more benefits than your previous one? How? 

26. What are the steps you are following to tackle these problems? Will it give 
a positive result? 

27. How are you managing the situation as you face these problems? 

28. What are all the other places affected by this fish invasion, and who are all 
the victims of the tank cleaner fish invasion? 

29. Did you file any complaints regarding these problems with any officials? 

30. Did they take any actions? 

31. Similar to this fish species, are there any other fish or other organisms 
causing problems to your people? 

iii) Conclusion Portion of the Interview 

1. Is there anything more you want to tell us? 

2. Do you have any questions for us? 

 

 


