Food of two size-groups of the catfish Mystus giulio (Hamilton-Buchanan) in Vemblai canal, Vypeen Island Item Type article Authors Ritakumari, S.D.; Ajitha, B.S.; Balasubramanian, N.K. Download date 26/09/2021 21:53:39 Link to Item http://hdl.handle.net/1834/33313 J. Indian Fish. Assoc., 33: 11-17,2006 II FOOD OF TWO SIZE-GROUPS OF THE CATFISH MYSTUS GULlO (HAMILTON-BUCHANAN) IN VEMBLAI CANAL, VYPEEN ISLAND S.D. Ritakumari, B. S. Ajitha and N. K. Balasubramanian Department ofAquatic Biology and Fisheries, University ofKerala, Thiruvananthapuram- 695 581, India ABSTRACT The stomach contents of two length-groups of the catfish Mystus gulio collected from Vemblai Canal in Vypeen Island (Kochi) were examined by frequency of occurrence and points methods. Analyses using standard indices proved difference in diet composition between the two size-groups. Keywords: Diet analysis, prey diversity, dietary breadth INTRODUCTION feeding ecology of Mystus gufzo by describing the diet and by assessing the The food habits of several fish competitive interaction between two species are well documented (Clepper, size-classes of fish. As culture of 1979) and the diets of many fish vary catfishes and air-breathing fishes need seasonally (Weisberg and Janicki, greater emphasis in coming years for 1990), often as a result of prey making use of large extent of our availability (Keast, 1985). However, swamps and derelict waters, such knowledge is far from complete as studies will be ofmuch relevance. regards the feeding ecology of fishes. Aspects such as the cause of differences MATERIAL AND METHODS in species composition between habitats, the extent of food resource The fish samples were collected partitioning in the assemblage and the from January to April 2002 using cast importance of competitive interaction nets from Vemblai Canal in Kuzhupilly between size-classes and/or species of Panchayath located north of Vypeen fishes are unknown (Gibson and Ezzi, Island, Kochi. This canal has direct link 1987). Hall et al. (1990) pointed out with the Kochi Backwaters, Kerala. that analyses of feeding patterns and use Heavy growth of mangrove vegetation of diet statistics to formally describe the occurs along the canal. variation in diet composition between species or between size-classes can be M. gulio collected during early used to reveal some of these aspects. hours of the day were anaesthetised and preserved immediately in 1Oo/o formalin In this paper, an attempt has been to halt digestion. In the laboratory, made to extend the knowledge on specimens (88 no.) ranging in standard 12 S. D. Ritakumari. B. S. Ajitha and N. K. Balasubramanian length from 7.8 to 15,1 em were are distributed in the diet was calculated grouped into two length-groups, viz., as follows: Size-group I (7.8- 10.7 em) and Size­ e= H group II (10.8 em and above). The stomach contents of all the collected specimens were analysed. Empty where Hmax = ln S and 1" S is the stomachs encountered in five natural logarithm of the number of food specimens were not included in the types. present study. The importance of diet items was assessed using the Index of similarity calculated occurrence method. An estimate of the using presence or absence and joined relative condition of each item was occurrence of food items was calculated assessed using the points method of by the following equation: Hynes (1950). S= 2c Prey-diversity was calculated A+B using the Shannon-Wiener infonnation measure (H ) (Shannon and Wiener, where A and B are· the number of 1949): different prey items in fishes of size­ groups I and II, and c is the number of s joint prey items shared by the two size­ H= :E (pi) In (pi) groups. i=1 where pi is the proportion of each RESULTS different food item contributing to the whole diet. Analysis of diet The data form the dietary analyses The dietary analysis showed that were used to calculate diet breadth, the fish feeds both on plant and animal using the niche width index (B) matter, and the stomach contents do not described by Levins ( 1968): differ qualitatively with the size offish. B= 1 The food items identified in the :E[pi]2 stomachs included blue-green algae, filamentous algae, diatoms, plant This index was used to compare remains, rotifers, calanoids, and parts of 'specialist' tendencies between insects and prawns. Plant remains species/size classes, with low values of formed the most preferred food item in the index indicating specialists and high size-groups I and II as they made their values generalists (Gibson and Ezzi, presence in 91.7% and 70.0%, 1987) .. respectively, of the stomachs sampled. Prey evenness (Pielou, 1966) that Filamentous algae formed the next measures how evenly the prey species preferred · item with more than 50% FOOD OF TWO SIZE-GROUPS OF THE CATFISH MYSTUS GULlO 13 (HAMILTON-BUCHANAN) IN VEMBLAI CANAL, VYPEEN ISLAND frequency of occurrence. Animal food frequently in the large size-group (Table items such as prawn remains, calanoids 1). and insect parts were encountered more Table 1: Food items ingested by Mystus gulio: Frequency of occurrence and percentage composition Freguency of occurrence Percentage com~osition Food item Size- Size- Size- Size- Total Total group I group II group I group II Blue-green algae 29.2 15.0 22.7 6.7 3.9 5.5 Filamentous algae 54.2 55.0 54.5 18.5 16.3 17.5 Diatoms 20.8 10.0 15.9 02.6 1.0 1.9 Plant remains 91.7 70.0 81.8 52.9 47.9 50.6 Rotifers 20.8 0.0 11.4 7.4 0.0 4.1 Crustaceans 20.8 35.0 27.3 6.3 9.6 7.8 Insect parts 16.7 25.0 20.5 4.8 10.9 7.5 Prawn 2arts 4.2 40.0 20.5 0.8 10.4 5.1 Analysis of percentage contribution slightly decreased with composition of the food of the species increase in the size of fish. An increase showed that the main item of the diet in consumption of animal remains with was formed of plant remains (50.6). increase in size of fish was also noticed Filamentous algae were also important in the study. in the diet (17.5o/o) ofthe species. Other non-animal foods assumed almost Niche measurement equal importance (Table 1). Though the percentage compositions of plant The diversity indices of the two remains and filamentous algae were size groups are presented in Table 2. H high in fishes ofboth size-groups, their values vary slightly between the two Table 2: Prey diversity indices of the two size-groups Index Size-group I Size-group II Shannon-Wiener information measure ( H ) 1.477 1.52i3 Diet breadth (B) 3.011 3.454 Prey evenness (e) 0.710 0.783 14 S. D. Ritakumari, B. S. Ajitha and N. K. Balasubramanian size-groups, suggesting a little higher feeding regimes. Mirza and Ahmed trophic diversity for the large-sized (1981) noticed seasonal variation in individuals than the small conspecifics. feeding in M. bleekeri. Biological Dietary breadth (B) indicates a wider studies of the freshwater catfish M. dietary niche for larger individuals than keletius was carried out by for small-sized ones, B values being Santhanakumar and Job (1984.) The 3.45 for large group and 3.01 for small food of M. vittatus from the highly group. Prey evenness values were also polluted Hussain Sagar Lake was marginally higher for Size-group II studied by Reddy and Rao (1993). (0.783) than for Size-group I fishes Vinci (1986) studied the biology of M. (0.710). The Similarity index'S' was seenghala from the. reservoirs of calculated as 0.93 in the study. Andhra Pradesh. DISCUSSION M. seenghala, the important commercial catfish of riverine systems In the present investigation, M. has been reported to feed on fishes by gulio was found to be an omnivore, earlier workers (Alikunhi and Rao, subsisting both on animal and plant 1948; Saigal and Motwani, 1961; matter from its surroundings. Pandian Sehgal, 1967; Bhatt, 1970; Vinci, 1986; ( 1971) studied M. gulio in the Cooum Shrivastava, 1993). However, Backwater (Madras) and found the cannibalistic habit as reported by Bhatt species as an omnivore. Jhingran (1970) could not be noticed by later (1982) reported that M gulio, the workers. Examination of gut contents euryha1ine catfish occurring mostly in of M. bleekeri revealed that it feeds freshwater and also in brackishwater of mainly on insects and their i larvae, low salinity, is predominately a crustaceans, molluscs and other carnivore, feeding mainly on planktonic organisms (Das and Moitra, crustaceans, molluscs and insect larvae. 1963; Pandey, 1983; Shrivastava, 1993). Both plant (algae and other Food and feeding habits of other hydrophytes) and animal matter form Mystus spp. have also been studied. the food of M. vittatus (Bhatt, 1971a; Dietary components of M. aor from Reddy and Rao, 1993). Studies on food, Ganga river system was analysed by feeding biology and the morphology of Saigal (1967). Bhatt (1970, 197la, b) associated organs of tropical catfish M studied the feeding biology of M. nemurus of Malaysia by Khan et al. seenghala, M vittatus and M cavasius. ( 1988) indicated that the species is According to McConnel (1975), usually euryphagous, feeding mystids in African lakes are carnivores extensively on a wide variety of food in general. Bordet ( 1979) and items in the bottom substrate. Thus, Sastrawibawa (1979) observed that M ditierent species of Mystus show nemurus in the Indonesian Archipelago diversified feeding regimes. is an omnivore with wide range of FOOD OF TWO SIZE-GROUPS OF THE CATFISH MYSTUS GULlO 15 (HAMILTON-BUCHANAN) IN VEMBLAI CANAL, VYPEEN ISLAND Variation in diet as a function of wider for large fish as compared to size has been reported in a large number small fish.