Int. J. Aquat. Biol. (2017) 5(6): 370-374 DOI:  

ISSN: 2322-5270; P-ISSN: 2383-0956

Journal homepage: www.ij-aquaticbiology.com 
© 2017 Iranian Society of Ichthyology 

Original Article 
Comparative ultrastructural study of general body epidermis of the hill-stream fishes; Botia 
almorhae (Teleosti: Botiidae), Homaloptera brucei (Teleostei: Balitoridae) and Schizothorax 

richardsonii (Teleostei: Cyprinidae) 
  

Hoshiyar Singh*1, Ila Bisht2 

 
1Department of Zoology, Surajmal Agarwal Degree College Pulbhatta, Kichha, U.S. Nagar, K.U. Nainital, India. 

2Department of Zoology S.S.J. Campus Almora, K.U. Nainital, 262522, India.

 

 

 

 

 

 

Article history: 
Received 9August 2017 

Accepted 23 October 2017 

Available online 2 5 December 2017 

Keywords:  
Epidermis 

Surface architecture 

Hill-streams 

GBE 

Abstract: The aim of the present study is to provide a basis for better knowledge of the surface 
architecture of the GBE of some hill-stream fishes. The skin of the hill- stream fishes, on the dorsal 
surface of the body just behind the head, is densely set with scales and composed of an epidermis 
and a dermis supported by a hypodermis. Noticeable differences exhibited in the patterns of 
microridges on epithelial cells, distribution of mucous cells and presence of tubercles on the general 
body epidermis of the hill-stream fishes may be considered as modifications relating to possible 
difference in the functional requirement at the different locations. The skin has long been recognized 
to protect the organisms from deleterious environmental impacts (physical, chemical, 
microbiological). It is also well-known to be crucial for the maintenance of temperature, electrolyte 
and fluid balance. 
 

  
Introduction 

The hill-stream fishes are well-adapted to specialized 

conditions of their life in torrential environment, 

where velocity of water current is high. Fishes living 

in hill-streams show several important modifications 

and may be conveniently divided into two groups. The 

members of one group are temporary inhabitants of 

the hill-streams and migrate upwards only at certain 

periods of their life for specific purposes such as 

spawning. These species move up by muscular effort 

and do not exhibit special modifications. Whereas 

other live permanently in the rivers and streams of the 

hills such as members of the families Cyprinidae (e.g. 

Garra, Schizothorax, Schizothorax, Barbus and 
Crossocheilus), Balitoridae (e.g. Balitora), 
Psilorhynchidae (e.g. Psilorhynchus), Nemacheilidae 
(e.g. Nemacheilus), and Sisoridae (e.g. Glyptothorax 
pectinopterus and Pseudocheneis sulcatus) that have 
specialized organs to live in such an environments. 

Some fishes in the hill-streams of India are 

represented by the genera belonging to the families 

                                                           
*Corresponding author: Hoshiyar Singh                                                                                DOI: https://doi.org/10.22034/ijab.v5i6.330 

E-mail address: singh.hoshiyar320@gmail.com 

Cyprinidae, Botiidae and Balitoridae. These fishes 

show a remarkable uniformity in their body contours. 

Dorsally their body is slightly arched, while ventrally 

it is usually flat from snout to anus. The aim of the 

present study is to provide a basis for better knowledge 

of the surface ultrastructural of the general body 

epidermis (GBE) of three hill-stream fishes, including 

Botia almorhae, Homaloptera brucei and Schizothorax 
richardsonii. 
 

Materials and Methods 

The live B. almorhae (127-177 mm in total length) 
were collected from the Kosi River at Kakrighat of 

District Nainital (1200 m. above sea level (asl)), 

H. brucei (76-101 mm in total length) from West 
Ramganga at Chaukhutia in District Almora (1200 m 

asl) and S. richardsonii (152-203 mm in total length) 
from the Kosi River at Hawalbagh in District Almora 

(1194 m asl) Uttarakhand. The water current was very 

fast having the velocity between 0.5 to 2.0 m/sec 

(Bhatt and Pathak, 1991) and the river bed is rocky. 



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Int. J. Aquat. Biol. (2017) 5(6): 370-374 

 

The collected fishes were transferred to the laboratory 

in well-ventilated plastic containers and kept for 5-6 

days in glass aquaria having an artificially prepared 

rocky bed with aquatic vegetation grown therein. The 

aquaria were cleaned and supplied with fresh spring 

water on alternate days. The fishes were fed on aqua 

feed (tropical fish food).  

The following procedure was adopted for the 

preparation of the specimen for SEM. The maintained 

specimen in laboratory at 25±2°C were cold 

anesthetized based on Mittal and Whitear (1978), for 

SEM preparation. Skin fragments of about 10×10 mm 

were cut from their dorsal sides just behind their 

heads. Tissue were excised and rinsed in 70% ethanol 

with one change of saline solution to remove debris 

and then fixed in 3% Glutaraldehyde in 0.1M 

phosphate buffer at pH 7.4 overnight at 4°C in a 

refrigerator. The tissues were washed with 2-3 

changes in phosphate buffer and dehydrated in 

ascending series of ice cold Acetone (30%, 50%, 70%, 

90% and 100% approximate 20-30 mins.) and dried at 

critical point using a critical point dryer (BIO-RAD 

England) with liquid carbon dioxide as the transitional 

fluid. Tissues were glued to stubs, using conductive 

silver preparation (Eltecks, Corporation, India). The 

samples were coated with gold using a sputters coater 

(JFC 1600) and examined under (JEOL, JSM- 6610 

LV) scanning electron microscope and the images 

were observed on the screen. 

Results 

The skin covering the general body surface of 

B. almorhae, H. brucei and S. richardsonii are rough 
and covered with a large number of scales. In 

B. almorhae, the entire external body surface is 
covered by minute scales; however those of in 

H. brucei and S. richardsonii have large number and 
small scales, respectively. Each scale is covered 
externally by the epidermis which reaches the 

posterior free margins transversing a short distance on 

its inner surface and then continue to the outer surface 

of the underlying scale.  

The polygonal epithelial cells are shown in the 

GBE of B. almorhae, H. brucei and S. richardsonii 
(Figs. 1, 2, 3); the free surface of the epithelial cells is 

differentiated into microridges, forming characteristic 

patterns.  

In B. almorhae, the epithelial cells bear numerous 
short, sinus and branched interwoven microridges 

(Fig. 4). However the finger print-like patterns of 

microridges are often shown on the surface of the 

epithelial cells of H. brucei and S. richardsonii (Figs. 
5, 6). These type microridges are often interconnected 

with fine transverse connections, the microbridges 

(Fig. 7), these microbridges shown only in GBE of 

H. brucei and S. richardsonii.  
In B. almorhae,the epithelial cells bear microridges 

and are commonly associated with mucus secreting 

cells, the mucous cells, which are scant in number  

Figure 1. SEMPH (Scanning electron microphotograph) of the GBE of Botia almorhae showing polygonal epithelial cells (marked by arrow) (Scale 
bar=10 μm). 

Figure 2. SEMPH of the GBE of Homaloptera brucei showing polygonal epithelial cells (marked by arrow) (Scale bar=5 μm). 
Figure 3. SEMPH of the GBE of Schizothorax richardsonii showing polygonal epithelial cells at high magnification (marked by arrow) (Scale bar 
=5 μm). 



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Singh and Bisht / Ultrastructural study of general body epidermis in three hill-stream fishes 

(Fig. 8) while the mucous cell apertures are rare 

comparatively and occur at the border of three or four 

epithelial cells in H. brucei (Fig. 9) but the mucous 
cells, though distributed throughout the epidermis are, 

in general, concentrated mainly on the outer layer of 

the epidermis, often releasing their secretory contents 

profusely at the surface through small pores in the 

S. richardsonii, (Fig. 10).  
A large number of tubercles are found on the 

epidermal surface of H. brucei, these tubercles exist in 
a well-designed pattern. The unculi are equidistantly 

placed and supported by epithelial cells. Polygonal 

outlining of the epidermal cells is seen at the base of 

the unculi, indicating unculi to be modified epithelial 

cells (Figs. 11, 12), all these structures are not shown 

in the GBE of B. almorhae and S. richardsonii. 

Discussion 

The epidermis is ectodermal in origin and consists of 

several layers of simple cells, of which the outer are 

being constantly worn away by wear and tear and 

replaced by newer ones which develop at their base. 

These layers of cells are composed of flattened cells, 

known as epithelium cells, of which the deepest layers 

are made up of columnar cells forming the stratum 

germinativum in which cells are always multiplying 

by mitotic division to replace the outer worn out cells. 

A superficial layer of dead horny cells, forming the 

stratum corneum is not present in fishes as an 

adaptation to life in water (Khanna, 1993). 

The epidermis of the GBE of B. almorhae and the 
structures associated with them show considerable 

structural modifications. These may be considered as 

Figure 4. SEMPH of the GBE of Botia almorhae epidermis showing microridges at the surface epithelium (Scale bar=5 μm). 
Figure 5. SEMPH of the GBE of Homaloptera brucei showing that the microridges are generally; finger print- like, and are often arranged in the 
form of small groups (Marked by arrows) (Scale bar =5 μm). 

Figure 6. SEMPH of the GBE of Schizothorax richardsonii showing finger print-like patterns of microridges (Marked by arrows) (Scale bar=10 
μm). 

Figure 7. SEMPH of the GBE of Schizothorax richardsonii showing finger print-like patterns of microridges that have canaliculi and microbridges 
(Marked by arrows) (Scale bar =5 μm). 

Figure 8. SEMPH of the GBE of Botia almorhae showing the opening of mucous cells (marked by arrows) (Scale bar=50 μm). 
Figure 9. SEMPH of the GBE of Homaloptera brucei showing the openings of mucous cells (marked by arrows) (Scale bar=10 μm). 



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Int. J. Aquat. Biol. (2017) 5(6): 370-374 

 

adaptations in relation to its peculiar habit and habitat. 

Homaloptera brucei is adapted to live in hill-streams 
characterized by fast flowing current under boulders. 

It is found in mountain streams (high gradient 

streams). The general body epidermis of H. brucei, 
exhibits compactly arranged microridges forming 

intricate mesh-like patterns, which are characteristic 

of the habitat under the boulders and stones. 

Furthermore, these microridges may gain a firm base 

and support from a dense network of fine filaments. 

The free surface of each epithelial cell is characterized 

by the presence of a series of microridges. The 

microridges of the cells appear smooth and uniform in 

width. Frictional force is less under boulder and 

stones; therefore, the requirement of lubrication is 

minimum in H. brucei. The epidermis of H. brucei 
possesses a large number of elevations distributed at 

irregular intervals. The epidermis with elevations 

alternates with that of the non-elevated surface. The 

average thickness of the epidermis varies in the two 

regions of H. brucei (Non-elevated region: 61.7 μm, at 
elevated region: 85.9 μm) (Bisht, 1999). Breeding 

tubercles are keratin based epidermal nodules, which 

are found in at least fifteen families of fishes in four 

orders. Breeding tubercles might offer a workable tool 

for examination of sexual selection among Cyprinids. 

The large number of tubercles in males indicates 

increasing reproductive power of the fishes. The 

primary function of the epidermis is to provide 

protection against environmental hazards. In fish, this 

function is mainly attributed to the gland cells which 

secrete their contents on the surface (Singh, 2014). 

In the general body epidermis of H. brucei and 
S. richardsonii finger print-like microridges, may in 
addition impart firm consistency or rigidity to the free 

surface of the epithelial cells. This could be 

considered as an adaptation to withstand mechanical 

stress and protect the surface of the fish, which has the 

characteristic habit of bottom dwelling. This specific 

pattern of microridges helps in the spreading of mucus 

from mucous cells over a wide area. The sudden 

spread of mucus is facilitated by numerous canaliculi 

formed by epidermal microridges. The abundance of 

mucus on the skin of S. richardsonii exhibits its habitat 
in open water or bottom dwellings, where frictional 

force is very high. This study indicates that the 

presence of mucus secretion is performing multi-

functional activities, assisting the fish to adapt to their 

characteristic mode of life for their maintenance 

against adverse environmental conditions, to which 

these are exposed. On the other hand open water 

surfaces have more pathogenic agents, which affect 

the epidermis; therefore, S. richardsonii has a greater 
more requirement of mucus. It also renders the skin 

less permeable and prevents the entry of pollutant 

materials and micro-organisms, which would 

otherwise infect the fish. Fish skin is a multipurpose 

tissue that serves numerous vital functions including 

Figure 10. SEMPH of the GBE of Schizothorax richardsonii showing the mucous openings and their secretory contents profusely at the surface 
through a small pore. (Marked by arrows) (Scale bar=10 μm). 

Figure 11. SEMPH of the GBE of Homaloptera brucei showing the well-developed tubercles at high magnification (marked by arrows) (Scale bar 
=200 μm).  

Figure 12. SEMPH of the GBE of Homaloptera brucei of showing polygonal epithelial cells and unculi on the tubercles (Marked by arrow) (Scale 
bar=10 μm). 



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Singh and Bisht / Ultrastructural study of general body epidermis in three hill-stream fishes 

chemical and physical protection, sensory activity, 

behavioural purposes or hormone metabolism. 

Further, it is an important first line defence system 

against pathogens, as fish are continuously exposed to 

multiple microbial challenges in their aquatic habitat 

(Rakers et al., 2010). Studies of fish skin indicated that 

epidermal cells follow separate pathways of 

differentiation in different fishes. In most of the fishes, 

the epidermis is related more to the deposition of slime 

over its surface and undergoes the process of 

mucogenesis and in some the epidermal cells undergo 

the process of keratinization forming a layer at the 

surface (Singh and Bisht, 2014). 

 

Acknowledgments 

We are grateful to all the people who helped in 

different part of this work especially the Department 

of College of Veterinary and Animal Sciences, G.B. 

Pant University of Agriculture and Technology, Pant 

Nagar (U.K.), for providing necessary instruments for 

this research work. Thanks are also due to M.P. Singh 

for his technical support. 

 

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