Int. J. Aquat. Biol. (2021) 9(1): 41-54
ISSN: 2322-5270; P-ISSN: 2383-0956
Journal homepage: www.ij-aquaticbiology.com
© 2021 Iranian Society of Ichthyology
Original Article
Food habits, ecomorphological patterns and niche breadth of the squeaker, Synodontis
schall (Pisces: Siluriformes: Mochokidae) from Niger River in Northern Benin
Hamidou Arame1, Alphonse Adite* 1, Kayode Nambil Adjibade1, Rachad Sidi Imorou1, Edmond Sossoukpe2, Sonon P. Stanislas1
1Laboratory of Ecology and Aquatic Ecosystem Management, Department of Zoology, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin.
2Laboratory of Wetland Researches, Department of Zoology, Faculty of Science and Technology, University of Abomey-Calavi, Cotonou, Benin.
s
Article history:
Received 17 August 2020
Accepted 19 January 2021
Available online 2 5 February 2021
Keywords:
Conservation
Diet
Sustainable exploitation
Omnivore
Mochokidae
Abstract: The squeaker, Synodontis schall dominates the Mochokid fish sub-community in Niger
River in Northern Benin and shows a great economic and commercial importance. The diet of S.
schall has been analysed to evaluate the food habit and resource utilization in this regional River.
Fish samplings were made monthly from February 2015 to July 2016 using unbaited longlines and
traps, seines and experimental gillnets. The results indicated that S. schall is an omnivore foraging in
benthic and pelagic habitats with diet dominated by aquatic insects (34.32%), sand particles
(18.768%), macrophytes (13.415%), seeds (8.549%), roots (8.319%), detritus (5.344%), mollusks
(1.204%) and phytoplankton (0.6255%). The omnivore food habit depicted was also shown by the
ecomorphological analysis mainly the relative gut length (GL/SL) varying between 0.8 and 5. The
species showed high diet flexibility with high niche breadth ranging between 1.86 and 5.74.
Synodontis schall exhibited an ontogenetic diet shift that was also confirmed by Pianka’s diet overlap
indexes ranging between Øjk=0.54-0.93. The conservation and the sustainable fisheries exploitation
of S. schall require the reinforcement of fishing regulation, habitat protection and ecosystem follow-
up.
Introduction
Knowledge on diet composition and food habits of
fishes is important for habitat protection, species
conservation, fisheries management and fish culture
(Rosecchi and Nouaze, 1987; Adite et al., 2007; Kone
et al., 2007). Furthermore, dietary analysis gives a
better understanding of how food resources are shared
and constitutes a basic tool for assessing trophic
structure and fish’s capability to adapt to
environmental changes (Rosecchi and Nouaze, 1985;
Hajisamae et al., 2003; Adité et al., 2006; Berté et al.,
2008). In West Africa, catfishes are represented by
124 species, 24 genera and 8 families among which
the family of Mochokidae made about 48 species
(Paugy et al., 2004). Among Mochokids, Synodontis
is the most diverse genus comprising about 36 species
(Paugy and Roberts, 2004) with S. schall, the most
widespread and dominant species that occurs in most
African rivers such as Senegal, Gambia, Volta, Tchad,
and Niger (Paugy et al., 2003). In Niger River, Paugy
*Correspondence: Alphonse Adite DOI: https://doi.org/10.22034/ijab.v9i1.973
E-mail: alphonseadite@gmail.com
and Levêque (2004) reported 28 species for the genus
Synodontis, with S. schall, the dominant and the most
tolerant species to adverse environmental conditions
(Lowe-McConnell, 1987).
In some African water bodies, S. schall is described
as an omnivore feeding on macro-invertebrates,
macrophytes and detritus (Willoughby 1974; Hickley
and Bailey, 1987; Ofori-Danson, 1992). The species
reproduces all seasons with peaks in wet and flood
periods. In Niger River in Benin, to date, there is a gap
of information on the feeding patterns of S. schall and
no published work is available on its trophic ecology.
In Benin, S. schall dominated the Mochokid sub-
community in many rivers and streams such as
Oueme, Okpara, Zou, Sô, Hlan, Tove, Mono, and
Niger (Lalèyè et al., 2004; Montchowui et al., 2007;
Djidohokpin et al., 2017; Hazoume et al., 2017; Sidi
Imorou et al., 2019). In Niger River in Northern Benin,
Arame et al. (2019) reported only the genus
Synodontis comprising fourteen valid species, with
42
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
S. schall, the most abundant species making
numerically 74.50% of the Mochokid fish
assemblages (Arame et al., 2020). Despite the
abundance and fisheries importance of S. schall that is
intensively exploited in Niger River in Benin, nothing
is known about the feeding ecology and resource
utilizations. Successful fisheries management and fish
culture require knowledge on trophic ecology of the
target species. The current research aims to study the
diet composition and feeding habits of S. schall in
Niger River in Bénin.
Materials and Methods
Study area: The research area is the Niger River in
Northern Benin around Malanville township. This
region is located between 11°52'05″N and 3°22′59″E
at an altitude of 200 m, and extended on about 3,016
km². The Niger River is a regional running water that
stands as a frontier between the two neighbor
countries, Benin and Niger Republics. In Benin, the
three tributaries, Mékrou, Sota and Alibori of Niger
River caused severe inundations with a peak flood
reaching 275 Km2 that boosted a high fish productivity
(Welcomme, 1985; Moritz et al., 2006; Adjovi, 2006;
Adite et al., 2017). The Niger River valley shows
sandy-clayish and ferruginous soils showing plant
communities comprising rooted, floating and
submerged vegetation. A multi species artisanal
fisheries occurred on floodplains, pools, river
channels and involved many ethnic groups (Hauber,
2011; Arame et al., 2019; Adjibade et al., 2019).
Collection sites: Four stations were selected on Niger
River for the sampling of the fish species (Arame et
al., 2020): (1) Tounga village located at 11°52'216"N,
3°23'907"E constitutes a highly degraded site, (2)
Behind Dry Port, situated at 11°52'216"N,
Figure 1. (above) Internal organs and (below) structure of the digestive tract of Synodontis schall from Niger River in Northern Benin (1, Esophagus;
2, Stomach; 3, Cardiac stomach; 4 (above), Intestine; 4 (below), Anterior intestine; 5 (above), Rectum; 5 (below), Medium intestine; 6 (above),
Anal orifice; 6 (below), Rectum; 7, Posterior intestine; 8, Anal orifice).
43
Int. J. Aquat. Biol. (2021) 9(1): 41-54
3°23'907"E, is also degraded, (3) Money village,
located at 11°52'987"N, 3°20'819"E, is a less degraded
site, and (4) Gaya village, less degraded, is located at
11°52'675"N, 3°25'329"E in the river at Niger
Republic side.
Mochokid fish collections: Fish samplings were
performed monthly from February 2015 to July 2016
in aquatic vegetation and in open water habitats at the
four stations. Unbaited longlines and traps, seines and
experimental gillnets were used for the samplings.
Collection procedures follow Adite et al. (2013).
Mochokid samplings were also performed from
fishermen artisanal catches on the basis of 1/3 of
species abundance when the abundance exceeded 50
individuals. All individuals were retained for the
sample when the abundance is less than 50 for a given
species (Kakpo, 2011; Okpeicha, 2011). The fishes
were then identified in situ based on Van Thielen et al.
(1987) and Levêque and Paugy (2006). Identified
fishes were preserved in 10% formalin and transported
to Laboratoire d’Ecologie et de Management des
Ecosystèmes Aquatiques (LEMEA), at the Faculty of
Sciences and Technics, in the University of Abomey-
Calavi. In the laboratory, fish individuals were
transferred into 70% ethanol to facilitate biological
observations. http://www.fishbase.org (Froese and
Pauly, 2018) were used to confirm fish species.
Dietary analysis: After sampling, each individual
was measured for total length (TL) and standard
length (SL) to the nearest 0.1 mm with an ichtyometer,
and weighed to the nearest 0.01 g with an electronic
balance (CAMRY 0.1 g / 500 g; AWS). Each
individual was then dissected and the gut was removed
and measured (Adite et al., 2007; Gbaguidi et al.,
2016). The stomach was then opened and food
resources were removed and spread on a glass slide for
examination first under a binocular to identify
macroscopic foods items. Then, a photonic
microscope was used to identify fine food resources
and algae (Adite et al., 2017). References such as
Needham and Needham (1962), Bourrelly (1985,
1990) and Tachet et al. (2010) were used to identify
prey items at the lowest possible taxonomic level. The
volume (V) of each food resource identified from the
1505 stomach dissected was estimated by water
displacement following Adite and Winemiller (1997).
Data analysis: The estimated volume (V) and counts
of each identified food item were recorded on Excel
software spreadsheet and the proportional volumetric
consumption (%V) of each food item was computed
using the formula (Adite and Winemiller, 1997):
%V =Vi
Vt
× 100
Where, %V is the proportional volumetric
consumption of food item i in the diet, Vi is the total
volume of the food item i in n stomachs, Vt is the total
volume of food resource ingested by n stomachs, and
n is the total number of stomachs dissected. The
volumetric proportions of each food item consumed
were calculated for different size classes to examine
ontogenetic diet shifts. The analysis of variances
(ANOVA) was run with SPSS software (Morgan et
al., 2001) to assess spatial and seasonal variations in
diet. Empty stomach indexes (Ce) were computed as
the ratio of number of empty stomachs to total number
of stomachs examined:
Ce = Ni
Nt
×100
Where, Ce is the coefficient of emptiness, Ni is the
number of empty stomachs and Nt is the total number
of stomachs examined. The following formula of
Bahou et al. (2007) was used to estimate the
occurrence frequency (OF) of each food resource in
the diet:
OF= Ji
Nt
×100
Where, Ji is the number of stomachs containing
prey item i and Nt is the total number of non-empty
stomachs. According to Sorbe (1972), the prey is
classified “accidental”, “secondary” and
“preferential” when OF<10%, OF between 10 and
50% and OF>50%, respectively. Diet breadth (DB)
was computed following Simpson (1949):
Diet breadth (DB) = ∑
=
n
i
iP
1
21
Where, Pi is the proportion of food resource i in the
diet and n is the total number of food items in the diet.
In general, the DB ranges from 1 (when only one food
resource is ingested), to n in case all food resources
44
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
are ingested in equal proportions. The values of DB
were submitted to ANOVA using SPSS software
version 21 (Morgan et al., 2001) to show the variation
among life stage. Pianka's diet overlap index (Øjk)
(1976) was computed between fish size classes to
examine diet similarities and ontogenetic diet shift:
∅jk =
∑ ∑
∑
= =
=
×
n
i
n
i
ikij
n
i
ikij
PP
PP
1 1
22
1
Where, Øjk is the Pianka’s dietary overlap between
species j and species k, Pij is the proportion of resource
i used by species j, Pik is the proportion of food item i
used by species k and n is the number of food resource
ingested. The eco-morphological analysis of the diet
was evaluated using the linear regressions between gut
length (GL) and body weight (W) and between gut
length (GL) and standard length (SL). Likewise, the
ratio (GL/SL) was computed as a measure of relative
gut length and compared to published reference ratios
0.8 to 5 for omnivores (Al-Hussaini, 1947; Kapoor et
al., 1975). Also, the eco-morphological patterns were
examined to document the food habit of S. schall.
Results
The digestive tract of S. schall: The morphology of
digestive tract showed a thick-walled esophagus
followed by a well-developed fork-like shape
stomach, an intestine (anterior, medium and
posterior), a rectum and an anal orifice (Fig. 1). The
pyloric caecum is absent.
Diet composition: In Niger River, S. schall foraged
mainly in pelagic and benthic habitats where the
species consumed about 221 food resources
dominated by aquatic insects (34.32%), sand particles
(18.768%), macrophytes (13.415%), seeds (8.549%),
roots (8.319%), detritus (5.344%), worms (4.735%)
and rice hulls (3.681%), aggregating 97.131% of the
stomach content (Table 1). Minor preys were mollusks
(1.204%), fish scals (0.796%), crustacean (0.161%),
zooplankton (0.083%) and phytoplankton (0.6255%)
(Table 1).
Seasonal variations of diet: Figure 2 shows
volumetric percentage (%) of preys consumed by
S. schall according to seasons. The results of the food
preys ingested showed significant (P<0.05) seasonal
variations for insects (F2,1502=5.855, P=0.003), seeds
(F2,1502=19.865, P=0.001), roots (F2,1502=18.029,
P=0.001), detritus (F2,1502=16.24, P=0.001),
phytoplankton (F2,1502=11.875, P=0.001),
zooplankton (F2,1502=15.142, P=0.001), macrophytes
(F2,1502=5.466, P=0.004). Indeed, the highest
volumetric percentage of insects (44.67%) ingested
was recorded during flood while those of seeds
(19.34%), roots (11.63%) and detritus (8.57%) were
Figure 2. Seasonal variations of food resources consumed by Synodontis schall in Niger River in Northern Benin.
45
Int. J. Aquat. Biol. (2021) 9(1): 41-54
Table 1. Volumetric, occurrence and numeric percentages of prey items ingested by Synodontis schall from Niger River in Northern Benin.
Prey category Prey / family/genus / species
Volumetric
Percentage
(%V)
Number
(N)
Numeric percentage
(%N)
Phytoplankton
Blue algae Cyanophyceae 0.096 435 5.226
Green algae
Chlorophyceae 0.181 942 11.318
Trebouxiophyce 0.004 22 0.264
Ulvophyceae 0.002 11 0.132
Desmids
Eustigmatophyceae 0.002 14 0.168
Zygnematophyceae 0.004 21 0.252
Diatoma
Bacillariophyceae 0.22 1098 13.192
Coscinodiscophyceae 0.051 179 2.151
Mediophyceae 0.032 174 2.091
Undetermined
h l k
Unidentified phytoplankton 0.034 314 3.773
Total phytoplankton 0.6255 1765 38.568
Zooplankton
Branchiopoda
Cladocerans 0.014 3 0.036
Copepods 0.032 4 0.048
Rotifera Brachionidae 0.038 2 0.024
Total zooplankton 0.083 9 0.108
Worms
Nematoda 3.138 433 5.202
Annelides oligochaetes 1.571 20 0.240
Glossiphoniidae 0.026 2 0.024
Total worms 4.735 455 5.467
Insects
Ephemeroptera
Leptohyphidae 0.189 3 0.036
Ephemerellidae 0.039 4 0.048
Heptageniidae 0.124 3 0.036
Baetidae 0.131 4 0.048
Hydroptilidae 0.112 2 0.024
Siphlonuridae 0.112 2 0.024
Plecoptera
Pachygronthidae 0.004 2 0.024
Leuctra geniculata 0.025 1 0.012
Odonata
Libellulidae 1.128 53 0.637
Lestidae 0.175 4 0.048
Coenagrionidae 0.25 10 0.120
Calopterygidae 0.112 3 0.036
Aeshnidae 0.1 2 0.024
Heteroptera
Tettigoniidae 0.05 1 0.012
Notonectidae 0.037 1 0.012
Pleidae 0.05 2 0.024
Coleoptera
Aphodidae 0.006 1 0.012
Copridae 0.149 1 0.012
Coenagrionidae 0.093 2 0.024
Curculionidae 0.301 13 0.156
Dytiscidae 0.137 4 0.048
Elmidae 0.398 7 0.084
Elminthidae 0.121 3 0.036
Ecnomidae 0.003 2 0.024
Hydraenidae 0.243 10 0.120
Hydrochidae 0.065 7 0.084
Hydrophilidae 6.731 250 3.004
Hydroporinae 0.162 4 0.048
Noteridae 0.1 1 0.012
Pleidae 0.1 1 0.012
Psephenidae 0.025 1 0.012
Tricoptera
Agupetidae 0.056 1 0.012
Philopotamidae 0.137 5 0.060
Sericostomatidae 0.028 5 0.060
Helicopsychidae 0.025 1 0.012
46
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
recorded during the wet period. Also, the highest
volumetric percentage of phytoplankton (0.73%) and
zooplankton (0.14%) consumed were recorded during
the dry season. Nevertheless, there were no significant
(P>0.05) seasonal dietary variations for mollusks
(F2,1502=0.055, P=0.946), rice hulls (F2,1502=0.510,
P=0.477), worms (F2,1502=0.275, P=0.760),
crustaceans (F2,1502=2.613, P=0.074), sand particles
(F2,1502=0.963, P=0.382) and fish scales
(F2,1502=2.527, P=0.080) (Fig. 2).
Frequency of occurrence in diet: The analysis of the
occurrence frequencies (OF) of the food resources
revealed that phytoplankton was ingested by all 1505
individuals collected with an occurrence frequency
OF=100% indicating that, though of reduced
volumetric percentage (0.6255%), phytoplankton
appeared to be the preferential prey. Also, insects,
sand particles and detritus with a huge aggregated
volumetric percentage (Vp=58.42%), displayed a high
OF estimated at 73.53, 59.19 and 59.11%,
respectively, that classified them as preferential preys
(Table 2). The secondary preys consumed were
worms, roots, zooplankton, seeds and macrophytes
that were common in some stomachs with moderate
OF ranging between 12.04 and 35.74% (Table 2). The
accidental preys, rice hulls, fish scales, mollusks, and
crustaceans ingested by S. schall occurred just in few
stomachs with reduced OF varying between 0.55 and
6.66%.
Diet according to life stages: The ontogenetic
analysis of the diet indicated that preys such as roots
(59.63%), insects (16.75%) and sand particles
(15.30%) dominated the stomach of juveniles. In
addition, macrophytes (15.97%) and rice hulls
(9.23%) consistently occurred in the stomach of sub-
adults, and insects (38.56%) relatively dominated the
diet of adults (Table 3). Overall, the three life stages
tended to consume more roots, insects and sand
Table 1. Continued.
Prey category Prey / family/genus / species
Volumetric
Percentage
(%V)
Number
(N)
Numeric percentage
(%N)
Insects
Hydroptidae 0.003 3 0.036
Hydropsychidae 4.051 310 3.725
Lepidostomatidae 0.152 6 0.072
Limnephilidae 0.025 2 0.024
Glossosomatidae 0.03 8 0.096
Polycentropodidae 0.165 2 0.024
Diptera
Chironomidae 9.918 621 7.461
Ceratopogonidae 1.388 60 0.721
Dasyheleinae 1.196 52 0.625
Chaoboridae 0.065 3 0.036
Psychodidae 0.006 3 0.036
Insects parts 3.812 179 2.151
Indetermine insects Unidentified insects 1.994 204 2.451
Total insects 34.32 1869 22.456
Total mollusks Mollusks Sphaeriidae 1.204 41 0.493
Crustacean
Branchipodidae 0.001 2 0.024
Platyischnopidae 0.008 2 0.024
Candonidae 0.106 2 0.024
Gammaridae 0.047 1 0.012
Total crustaceans 0.161 7 0.577
Fish scales Fish scales 0.796 59 0.709
Roots Roots 8.319 361 4.337
Seeds Seeds 8.549 170 2.043
Machrophytes Machrophytes 13.415 172 2.067
Rice hull Rice hull 3.681 84 1.009
Detritus Detritus 5.344 748 8.987
Sand particles Sand 18.768 1138 13.673
Total 100% 8323 100%
47
Int. J. Aquat. Biol. (2021) 9(1): 41-54
particles. The presence of sand in a high volumetric
percentage indicated that S. schall is a benthic feeder.
Macrophytes occurred only in the diet of sub-adults
and adults probably because their digestive tracts were
more developed than those of juveniles. The food
items consumed by different life stages of S. schall
showed significant (P<0.001) variations for insects
(F2,1502=26.943, P=0.001), roots (F2,1502=4.607,
P=0.001), rice hulls (F2,1502=2.5393, P=0.001),
worms (F2,1502=4.055, P=0.001), macrophytes
(F2,1502=23.24, P=0.001), seeds (F2,1502=21.370,
P=0.001), detritus (F2,1502=47.711, P=0.001).
However, there were no significant (P>0.05)
ontogenetic variations in the consumption of mollusks
(F2,1502=1.147, P=0.273), crustaceans (F2,1502=0.114,
P=0.758) and fish scales (F2,1502=0.29363, P=0.932),
phytoplankton (F2,1502=0.00127, P=0.129),
zooplankton (F2,1502=0.708, P=0.136) and sand
particles (F2,1502=9.482, P=0.29).
Empty stomachs: For this study, 1505 stomachs of
S. schall were examined and 243 of them were empty
(Table 4). In general, the coefficient of emptiness
varied with seasons and life stages and ranged
between 5.88 and 23.47%. Empty stomachs were
higher in adults and averaged 19.08±4.57% whereas
relatively lower percentages were recorded among
sub-adults (mean: 11.22±4.65%). In contrast, almost
all juveniles exhibited full stomachs and only one
individual was empty. Also, significant seasonal
variations of empty stomachs were recorded during
the study. Indeed, higher values were recorded during
the wet and flood periods where the coefficient of
Table 2. Occurrence frequencies of prey consumed by Synodontis schall from Niger River in Northern Benin.
Prey categories Occurrence frequency (%) Food importance
Phytoplankton 100.00 Preferential prey
Insects 73.53 Preferential prey
Detritus 59.11 Preferential prey
Sand particules 59.19 Preferential prey
Zooplankton 17.51 Secondary prey
Worms 35.74 Secondary prey
Seeds 13.15 Secondary prey
Machrophytes 12.04 Secondary prey
Roots 28.92 Secondary prey
Crustaceans 0.55 Accidental prey
Mollusks 3.25 Accidental prey
Fish scales 4.68 Accidental prey
Rice hulls 6.66 Accidental prey
Table 3. Ontogenetic variations of preys consumed (volumetric percentage) by Synodontis schall from Niger River in Northern Benin.
Volumetric percentage (%V)
Prey categories Juveniles (TL < 5) Sub-adults (5 ≤ TL < 8) Adults (TL ≥ 8)
Phytoplankton 0.5504 0.6008 0.6332
Detritus 0.0612 3.2259 5.6091
Roots 59.633 11.937 7.4895
Seeds - 6.8155 8.9774
Macrophytes - 15.9743 12.912
Rice hulls 6.1162 9.2315 2.4342
Worms 1.5291 3.4191 3.1153
Mollusks - - 1.3559
Crustaceans - - 0.1976
Zooplankton 0.0738 0.0032 0.0388
Insects 16.7458 25.1464 38.5602
Fish scales - 0.9225 0.7717
Sand particles 15.2905 22.7238 17.9051
Total 100% 100% 100%
48
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
emptiness reached 22.07 and 19.20%, respectively,
whereas that of dry season was relatively low with a
value of 14.16% (Table 4).
Pianka’s diet overlaps and ontogenetic diet shifts:
Overall, diet overlaps between size classes of S. schall
ranged from Øjk=0.54 (pairing "Juvenile X Sub-
adults") to Øjk=0.93 (pairing "Sub-adult X Adults")
and averaged Øjk=0.71±0.20 indicating relatively high
diet similarities among different life stage categories.
Nevertheless, the reduced Øjk=0.54 and Øjk =0.66
recorded respectively between "Juvenile" and "Sub-
adults" and between "Juvenile" and "adults" indicated
an ontogenetic diet shift (Table 5).
Diet breadth: In Niger River in Benin, S. Schall
consumed a wide range of food resources reaching
221 food items classified in 13 foods categories
(phytoplankton, detritus, roots, seeds, macrophytes,
rice hulls, worms, mollusks, crustacean, zooplankton,
insects, fish scales, and sand particles). Consequently,
a high diet breadth (DB=4.93) was recorded for the
Table 4. Seasonal variations of empty stomachs of Synodontis schall from Niger River in Northern Benin.
Life stage
Flood Dry Wet Total
Nt Ne Ec (%) Nt Ne Ec (%) Nt Ne Ec (%) Nt Ne Ec (%)
Juveniles<5 mm - - - 5 1 20 - - - 5 1 20
Sub-adults [5-8 mm] 14 2 14.3 252 34 13.49 17 1 5.88 283 37 13.07
Adults≥8 mm 247 48 19.4 774 111 14.34 196 46 23.47 1217 205 16.84
Total 261 50 19.2 1031 146 14.16 213 47 22.07 1505 243 16.15
Nt=Total number of stomachs, Ne= number of empty stomachs, Ec (%) = Coefficient of emptiness
Table 5. Matrix of diet overlaps (Øjk) by life stage category of Synodontis schall from Niger River in Northern Benin.
Length classes Juveniles (TL<5) Sub-adults (5≤TL<8) Adults (TL≥8)
Juveniles (TL<5) 1 0.54 0.66
Sub-adults (5≤ TL< 8) 1 0.93
Adults (TL≥8) 1
Table 6. Diet Breadth (DB) variations by life stage of Synodontis schall from Niger River in Northern Benin.
Length Classes (TS, cm)
Seasons Juveniles (TL<5) Sub-adults (5≤TL<8) Adults (TL≥8) Total
Wet - 4.44 5.22 5.32
Flood - 1.86 4.42 4.22
Dry 2.46 5.74 4.34 4.84
Total 2.46 5 4.45 4.93
Table 7. Spearman correlation coefficients between standard length (SL)/gut length (GL) and the volumetric percentages of food resources
consumed by Synodontis schall from Niger River in Northern Benin.
Prey categories
SL GL
r a (slope) b P-value r a (slope) b P-value
Phytoplankton 0.3162 23.1 10.30 0.842 0.3162 191 17.2091 0.374
Detritus 0.4472 3.506 10.2936 0.066 0.3317** 14.628 17.3040 0.0001
Roots 0.3162 0.88 10.3166 0.645 0.5477 7.437 17.3239 0.036
Seeds 0.4472 1.52 10.2873 0.090 0.3464** 7.150 17.3174 0.0001
Macrophytes 0.8944** 2.9363 10.2479 0.001 0.6325 4.104 17.3472 0.01
Rice hulls -0.8367** -8.63 10.4 0.001 -0.4899** -28.732 17.6907 <0.001
Worms -0.3873 -0.32 10.3353 0.876 -0.3162 -1.001 1.4751 0.793
Mollusks 0.3162 5.684 10.318 0.141 0.3162 3.610 17.4564 0.615
Crustaceans -0.3162 -3.12 10.3 0.799 -0.3162 -11.08 17.4687 0.626
Zooplankton 0.3162 6.667 10.3025 0.175 0.4000** 44.790 17.2657 0.0001
Insects 0.5000** 3.8133 10.0679 <0.0001 0.5916** 10.621 16.7272 <0.0001
Fish scales 0.3464 1.627 10.3293 0.831 0.3162 4.81 17.4567 0.735
Sand particles 0.4472* 2.569 102291 0.050 -0.3606 -1.280 17.5163 0.608
* : Correlation is significant at P=0.05 level, **: Correlation is significant at P=0.01 level.
49
Int. J. Aquat. Biol. (2021) 9(1): 41-54
whole population. Ontogenetically, the DB increased
with fish sizes and ranged between DB=2.46
(juveniles and DB=5 (sub-adults) (Table 6). Also, the
results showed seasonal variations in the diet breadth
with a higher value (DB=5.32) recorded during the
wet season whereas a relatively lower value
(DB=4.22) was recorded during the flood period
(Table 6).
Eco-morphological relationships: The diet of
S. schall was evaluated by plotting the volumetric
proportion of the food categories (phytoplankton,
insects, crustaceans, fish scales, mollusks,
zooplankton, worms, roots, seeds, detritus,
macrophytes, rice hulls and sand particles) against
standard length (SL) and gut length (GL) to explore
ecomorphological correlates of food habits. The
matrix of spearman correlation coefficients recorded
indicated that SL was positively correlated with the
volumetric proportions of insects (r=0.5000, P<0.01),
macrophytes (r=0.8944, P<0.01), sand particles
(r=0.4472, P≤0.05) and negatively correlated with
rice hulls (r=-0.8367, P<0.01). Also, GL was
positively correlated with detritus (r=0.3317, P<0.01),
insects (r=0.5916, P<0.01), seeds (r=0.3464, P<0.01)
and zooplankton (r=0.4000, P<0.01) and negatively
correlated with rice hulls (r=-0.4899, P<0.01) (Table
7). In addition, the regressions between SL-GL and
between W (weight)-GL were established to evaluate
the ecomorphological trends. The regression
equations were as follow: Log(GL)=1.0878Log(SL)
+0.1146, r=0.6007 (Fig. 4); and Log (GL)=0.4223Log
(W)+0.5981, r=0.6731 (Fig. 3). Both equations
indicated that GL increased with SL and weight with
significant (P<0.05) correlation coefficients. The ratio
(GL/SL) was also computed as a measure of relative
gut length and compared to published reference ratio
(Kramer and Bryant, 1995). GL/SL varied from 0.12
(SL=5 cm) to 5 (SL=9 cm) with a mean of 1.69±0.56.
Discussions
Food and feeding patterns: The dietary analysis
indicated that S. schall consumed a wide range of food
resources (221 food items) dominated by eight prey
categories such as insects (34.32%), sand particles
(18.768%), macrophytes (13.415%), seeds (8.549%),
roots (8.319%), detritus (5.344%), worms (4.735%)
and rice hulls (3.681%) aggregating 97.131% of the
stomach contents. This large food spectrum resulted
from the presence of numerous developed mandibular
teeth ranging between 24-39 and numerous gill rakers
Figure 3. Relationship between Log (gut length) and Log (body weight) of Synodontis schall (N=1505) from Niger River in North-Benin.
50
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
varying between 40-44 (personal records) on the first
branchial arch that could have favored this trophic
flexibility (Paugy and Roberts, 2003). Minor food
items were fish scales (0.80%), crustacean (0.16%)
and zooplankton (0.08%) and none of them had a
volumetric proportion more than 0.80%. The presence
of fish scales may indicate that this species had
tendency to lepidophag. This feeding pattern
suggested that in Niger River in Benin, S. schall
displayed an omnivorous feeding habit that was
confirmed by the presence of balanced animal and
plant matters in the stomach of S. schall (Dadebo et
al., 2014; Admassu et al., 2015).
These findings agreed with those reported by
Willoughby (1974) in Lake Kanji in Nigeria, by
Yatabary (1983) in the Central Delta of Niger River
and by Diomande et al. (2009) in the River-Lacustrine
hydrosystem of Bia in Ivory Coast where S. schall
foraged mainly on insect nymphs and larvae, fish
eggs, detritus, zooplankton, benthos, dipteran larvae,
animal fragments, fish scales, macrophytes and
sediment. Likewise, in Oueme River in Benin, Laleye
et al. (2006) reported identical food habits for S. schall
that foraged mainly on macrophytes, algae, insect
larvae, aquatic insects, crustacea, rotifera, molluscks,
nematoda, fish eggs, fish scales and sand particles.
Ecomorphological patterns and food habits: The
wide spectrum of food resources (221 foods items
recorded) ingested by S. shall in Niger River
suggested that this dominant Mochokid is an
omnivore. This food trend depicted is consistent with
the ecomorphology patterns of the species. Indeed, the
mean relative gut length (ratio: GL/SL) fall in most
omnivore ranges. These findings agreed with those
reported by Al-Hussaini (1947) and Kapoor et al.
(1975) where the relative gut length varied between
0.8 and 5 for omnivores while herbivore showed
higher ratio ranging between 2 and 21. As reported by
Dadebo et al. (2012), omnivore fishes forage both on
plant and animal items and tend to have a moderate to
short intestine with reduced relative gut length
(GL/SL). In contrast, herbivore fishes exhibit long
intestines with greater relative gut length (Al-
Hussaini, 1947; Fryer and Iles, 1972; Kapoor et al.,
1975).
Niche breadth, diet shift and trophic plasticity:
This opportunistic feeding habit displayed by S. schall
is the result of the high diet breadth (DB) varying
between 1.86 and 5.74 that were computed from the
221 food items identified. The body morphology, the
Figure 4. Relationship between Log (gut length) and Log (standard length) of Synodontis schall (N=1505) from Niger River in North-Benin.
51
Int. J. Aquat. Biol. (2021) 9(1): 41-54
feeding behavior and the various ecological niches
explored, greatly accounted for this wide spectrum of
food ingested. Indeed, the ventrally positioned mouth
of S. schall is adapted for benthic feeding. Also, the
fact that Synodontis is able to swim in upside down
position enables this genus to switch from benthic
feeding to surface/pelagic feeding depending on the
availability and emergence of some food items (Bishai
and Gideiri, 1965; Sanyanga, 1998). Nevertheless, as
S. schall grows and move to pelagic waters, this
Mochokid is limited in foraging large prey because of
its small mouth. However, its specialized teeth are
suited to pick scales from other fishes in pelagic
ecological niches (Fryer et al.,1955).
Although the proportional consumptions of the
food items were not equally represented in the diet, the
wide choice of foods available to S. schall suggested
that when one prey was in reduced supply, the species
could forage on another abundant and available prey.
As reported by Mbadu (2011), this can be, not only an
adaptation to reduce intraspecific competition among
individuals in different classes of size, but also an
indicator of trophic plasticity in S. schall which may
shift its feeding structure according to prey
availability (Adite et al., 2013; Gbaguidi et al., 2016).
The current study revealed ontogenetic diet shift of
S. schall. Indeed, juvenile foraged preferentially on
aquatic larvae (Chironomidae larva) while sub-adults
and adults ingested mainly macrophytes in
proportional consumptions of 15.97 and 12.912%,
respectively. In contrast, in Oueme River, Laleye et al.
(2006) reported S. schall juvenile foraging mainly on
macrophytes that accounted for 59.65% of the
stomach content while seeds, sand, roots, insects
(diptera and coleoptera) were the dominant food items
of sub-adults and adults. In Lake Chamo in Ethiopia,
Dadebo et al. (2012) reported the same diet shift
according to life stages. The differential development
of the digestive tract and the trophic flexibility could
have caused this ontogenetic diet shift in S. schall.
Also, the study consistently showed high diet
similarities between life stages indicated by a
relatively high diet overlaps ranging between
Øjk=0.54-0.93. However, the reduced diet overlaps
between juveniles (TL<5 cm) and sub-adults
(5≤TL<8 cm) confirmed the ontogenetic diet shift
depicted (Adite et al., 2005). These results are
consistent with those reported by Gbaguidi et al.
(2016) with Sarotherodon galilaeus from a man-made
Lake of Southern Benin.
Conclusion
This study documents the feeding ecology of S. Shall,
the dominant Mochokid in Niger River in Benin.
Synodontis schall is an omnivore foraging both in
benthic and pelagic habitats and consuming mainly
aquatic insects, macrophytes, sand particles, seeds,
roots, detritus, worms, rice hulls, mollusks and
phytoplankton that resulted in a large niche breadth
and a high trophic plasticity. The omnivorous food
habit was also shown by the ecomorphological
analysis. The species exhibited an ontogenetic diet
shift that was also indicated by Pianka’s diet overlap.
The reinforcement of fishing regulation, the protection
of habitats and the permanent ecological follow-up of
the river are required for the conservation and the
sustainable exploitation of S. schall.
Acknowledgement
We are grateful to the Laboratory of Ecology and
Aquatic Ecosystem Management (LEMEA) of the
Department of Zoology, Faculty of Sciences and
Technics of the University of Abomey-Calavi for
providing logistics and assistances. Many thanks to
M. Razack, B.G. Ikililou, A. Germard, L. Medard,
A.D. Didier, K. Bernard and the numerous fishermen
for their help in fish collections.
References
Adite A. (2007). Ecologie de Heterotis niloticus
(Osteoglossiformes: Osteoglossidae) du Systeme
fluviolacustre rivière So-lac Hlan (Sud-Bénin):
Conservation et interêt pour l’aquaculture. Ph.D.
Dissertation, Faculté des Sciences et Techniques,
Université d’Abomey-Calavi, Bénin.
Adite A., Winemiller K.O. (1997). Trophic ecology and
ecomorphology of fish assemblages in coastal lakes of
Benin, West Africa. Ecoscience, 4(1): 6-23.
52
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
Adite A., Imorou Toko I., Gbankoto A. (2013). Fish
assemblage in the degraded mangrove ecosystems of
the coastal zone, Benin, West Africa: Implications for
Ecosystem restoration and resources conservation.
Journal of Environmental Protection, 4: 1461-1475.
Adite A., Tossavi C.E., Kakpo D.B.E. (2017). Biodiversity,
length-weight patterns and condition factors of cichlid
fishes (Perciformes: Cichlidae) in brackish water and
freshwater lakes of the Mono River, Southern Benin,
West Africa. International Journal of Fauna and
Biological Studies, 4: 26-34.
Adjibade K.N., Adite A., Arame H., Sidi Imorou R., Sonon
S.P. (2019). Biodiversity and Community Structure of
Mormyridae (Pisces: Teleostei: Osteoglossiformes)
from Niger River in Northern Benin: Threats,
Conservation and Valorization Perspectives.
International Journal of Sciences, 8(5): 106-116.
Adjovi A.R. (2006). Monographie de la commune de
Malanville. Programme d'appui au démarrage des
communes, Afrique Conseil. 48 p.
Admassu D., Abera L., Tadesse Z. (2015). The food and
feeding habits of the African catfish, Clarias gariepinus
(Burchell), in Lake Babogaya, Ethiopia. Global Journal
of Fisheries and Aquaculture, 3(4): 211-220.
Al-Hussaini A.H. (1947). The feeding habits and the
morphology of the alimentary tract of some teleosts
living in the neighbourhood of the Marine Biological
Station, Ghardaqa, Red Sea. Publications of the Marine
Biological Station. Ghardaqa (Red Sea), 5: 1-61.
Arame H., Adite, A., Adjibade K.N., Sidi Imorou R., Sonon
P.S. (2019). Biodiversity of Mochokidae (Pisces:
Teleostei: Siluriformes) fishes from Niger River,
Northern Benin, West Africa: Threats and management
perspectives. International Journal of Fauna and
Biological Studies, 6(3): 25-32.
Arame H., Adite A., Adjibade K.N., Sidi Imorou R., Sonon
P.S. (2019). Biodiversity of Mochokidae (Pisces:
Teleostei: Siluriformes) fishes from Niger River,
Northern Benin, West Africa: Threats and management
perspectives. International Journal of Fauna and
Biological Studies, 6(3): 25-32.
Bahou L., Kone T., N’Douba V., N’Guessan K.J.,
Kouamelan E.P., Gouli G.B. (2007). Food composition
and feeding habits of little tunny (Euthynnus
alletteratus) in continental shelf waters of Côte d’Ivoire
(West Africa). -ICES Journal of Marine Science, 64:
1044-1052.
Berté S., Kouamélan E.P., Ouattara N.I., Koné T., N’Douba
V., Kouassi N’G.J. (2008). Régime alimentaire de
Distichodus rostratus (Characiformes, Distichodont-
idae) dans un bassin Ouest africain (fleuve Bandama,
Côte d’Ivoire). The Science of Nature, 5: 167-176.
Bishai H.M., Abu Gideiri Y.B. (1965). Studies on the
biology. II-Food and feeding habits. Hydrobiologia, 26:
98-113.
Blache J. (1964). Les poissons du bassin du Tchad et du
bassin adjacent du Mayo Kebbi. Etude Systematique et
Biologie O.R.S.T.O.M. Paris Cah. Mem. ORSTOM,
4(2): l-485.
Dadebo E., Aemro D., Tekle-Giorgis Y. (2014). Food and
feeding habits of the African catfish Clarias gariepinus
(Burchell, 1822) (Pisces: Clariidae) in LakeKoka,
Ethiopia African Journal of Ecology, 52: 471-478.
Djidohokpin G., Sossoukpe E., Sohou Z., Tamesse J.L.,
Fiogbe E.D. (2017). Ichthyofauna of Tovè river in the
south Benin: specific diversity and spatial distribution.
South Asian Journal of Life Sciences, 5: 19-29.
Froese R., Pauly D. (2018). FishBase. World Wide Web
electronic publication. www.fishbase.org, version
(06/2018).
Fryer G., Iles T.D. (1972). The Cichlid Fishes of the Great
Lakes of Africa: Their Biology and Evolution. Oliver
and Boyd, Edinburgh. 641 p.
Fryer G., Greenwood P.H., Trewavas E. (1955). Scale-
eating habits of the African cichlid fishes. Nature,
London, 175: 1089-1090.
Gbaguidi H.M.A.G, Adite A., Abou Y. (2016). Trophic
Ecology and Establishment of the Silver Catfish,
Chrysichthys nigrodigitatus (Pisces: Siluriformes:
Claroteidae) Introduced in an Artificial Pond of Benin,
West Africa. Journal of Fisheries and Aquatic Science,
12: 42-53.
Hajisamae S., Chou L.M., Ibrahim S. (2003) Feeding habits
and trophic organization of the fish community in
shallow waters of an impacted tropical habitat. Coastal
Shelf Science, 58: 89-98.
Hauber M.E. (2011). Description and Improvement of the
'Whedo'‐ Aquaculture ‐ System in Malanville (North of
Benin). Dissertation Zur Erlangung Des,
Naturwissenschaftlichen Doktorgrades Der
Bayerischen Julius‐Maximilians‐Universtität
Würzburg. 203 p.
53
Int. J. Aquat. Biol. (2021) 9(1): 41-54
Hauber M., Bierbach D. and Linsenmair K.E. (2011). New
records of fish species in the Niger River at Malanville
(North-East Benin). Bulletin of Fish Biology, 12: 79-82.
Hazoume R.U.S., Chikou A., Koudenoukpo C.Z., Adite A.,
Bonou C.A., Mensah G.A. (2017). Length-weight
relationships of 30 species of fish of the river Sô in
Benin (West Africa). International Journal of Fisheries
and Aquatic Studies, 5: 514-519.
Hickley P., Bailey R.G. (1987). Food and feeding
relationships of fish in the Sudd swamps (River Nile,
southern Sudan). Journal of Fish Biology, 30(2):147-
159.
Kakpo D.B.E. (2011). Biodiversité et Exploitation des
poissons du bas-Mono: implication pour la
Conservation et la Gestion durable des Ressources
Halieutiques. Mémoire de Master en Production et
Santé Animales, EPAC/UAC, Bénin. 105 p.
Kapoor B.G., Smit H., Verighina A.I. (1975). The
alimentary canal and digestion in teleosts. Advances in
Marine Biology, 13: 109-239.
Kone T., Kouamelan E.P., Ouattara N.I., Kicho A.V.
(2007). Regime alimentaire de Pomadasys jubelini
(Pisces, Haemulidae) dans lagune Ouest africaine
(lagune Ebrie, Cote d’Ivoire). Science and Nature, 4(1):
65-73.
Kramer D.L., Bryant M.J. (1995). Intestine length in the
fishes of a tropical stream. Environmental Biology of
Fishes, 42(45): 115-127.
Lévêque C., Paugy D. (2006). Les poissons des eaux
continentales africaines: Diversité, écologie, utilisation
par l'homme. Ed IRD. 573 p.
Lowe-McConnell R.H. (1987). Ecological studies in
tropical fish communities. Cambridge Tropical Biology
Series. Cambridge University Press, Cambridge. 178 p.
Mbadu Z. (2011). Biologie des espèces du genre
Distichodus Muller et Troschel, 1845
(Distichodontidae) du pool Malebo (Fleuve Congo) en
rapport avec les mécanismes d’exploitation de leurs
niches trophiques. Thèse Doctorale, Faculté notre Dame
de la Paix de Namur, Belgique. 442 p.
Montchowui E., Niyonkuru C., Ahouansou M.S., Chikou
A., Lalèyè P. (2007). L'ichtyofaune de la rivière Hlan au
Bénin (Afrique de l'Ouest). Cybium, 31: 163-166.
Morgan G.A., Grieggo O.V., Gloekner G.W. (2001). SPSS
for windows: An introduction to use and interpreta- tion
in research. Lawrence Erlbaum Associates, Publishers,
Mahwah. 240 p.
Moritz T., Lalѐyѐ P., Koba G., Linsenmair K.E. (2006). An
annotated list of fish from the River Niger at Malanville,
Benin, with notes on the local fisheries. Verhandlung
der Gesellschaf für Ichthyologie, 5: 95-110.
Needham G.J., Needham P.R.A. (1962). Guide to fresh
water biology, Edn 5, Holdon-Day Inc, San Francisco.
107 p.
Ofori-Danson P.K. (1992). Ecology of some species of
catfish Synodontis (Pisces: Mochocidae) in the Kpong
Headpond in Ghana. Environmental Biology of Fishes,
35: 49-61.
Okpeicha S.O. (2011). Biodiversité et exploitation des
poissons du barrage de la SUCOBE dans la commune
de Savè au Bénin, Mémoire de Master en hydrobiologie
Appliquée. FAST/UAC, Bénin. 43 p.
Paugy D., Lévêque C., Teugels G.G. (2003). Poissons
d'eaux douces et saumâtres de l'Afrique de l'Ouest.
Collection faune et flore tropicales, n°40,
MARC/MNHN/IRD, tome 1, Paris. 457 p.
Paugy D., Lévêque C., Teugels G.G. (2004). Faune des
poissons d’eaux douces et saumâtres de l’Afrique de
l’Ouest. Faune Tropicale. Edit. IRD. Paris. 815 p.
Paugy D., Roberts T.R. (2003). Mochokidae. In: C.
Lévêque, D. Paugy, G.G. Teugels (Eds.). Faune des
poissons d'eaux douce et saumâtres de l'Afrique de
l'Ouest, Tome 2. Coll. Faune et Flore tropicales 40.
Musée Royal de l'Afrique Centrale, Tervuren, Belgique,
Museum National d'Histoire Naturalle, Paris, France
and Institut de Recherche pour le Développement, Paris,
France. 815 p. pp: 195-268
Pianka E.R. (1976). Competition and niche theory. In:
R.M. May (Ed). Theoretical Ecology Principles and
Applications. Blackwell. London. pp: 114-141.
Rosecchi E., Nouaze Y. (1987). Comparaison de cinq
indices alimentaires utilisés dans l'analyse des contenus
stomacaux. Revue des Travaux de l’Institut des Pêches
Maritimes, 49: 111-123.
Sidi Imorou R., Adite A., Sossoukpe E., Abou Y. (2019).
Length-weight models and condition factors of fishes
from Okpara Stream, Oueme River, Northern-Benin.
International Journal of Forest Animal and Fisheries
Research, 3(3): 65-79.
Sorbe J.C. (1972). Regime alimentaire de Micromesistws
poutassou (Risso, 1826) dans le sud du Golfe de
Gascogne. Rev. Travaux de l’Institut de Peches
54
Arame et al./ Food habits of Synodontis schall from Niger River in Northern Benin
Maritime, 44(3): 245-255.
Van Thielen R., Hounkpe C., Agon G., Dagba L. (1987).
Guide de détermination des Poissons et Crustacés des
Lagunes et Lacs du Bas-Bénin. GTZ Direction des
Pêche, Cotonou, Benin. 285 p.
Welcomme R.L. (1985). River fisheries. Fisheries
Technical Paper 262, FAO, Rome. 95 p
Willoughby N.G. (1974). The ecology of the genus
Synodontis (Pisces: Siluriodei) in Lake Kainji, Nigeria.
University of Southampton, UK. Ph.D. dissertation. 288
p.
Yatabary N.T. (1983). Contribution à l'étude du régime
alimentaire de Synodontis schall insectes aquatiques de
Côte d'Ivoire. ORSTOM 42. 178 p.