Stomach content analysis of Cobia Rachycentron canadum (Linnaeus, 1766) from North West coast of in India

Indian Journal of Geo Marine Sciences Vol. 45 (12), December 2016, pp. 1631 1637 Stomach content analysis of Cobia Rachycentron canadum (Linnaeus, 1766) from North West coast of in India M.K. Sajeevan *1 & B. Madhusoodana Kurup 1 School of Industrial Fisheries, Cochin University of Science and Technology, Kochi 682016, India. * 1 Kerala University of Fisheries and Ocean Studies, Panangad, Kochi, India. [E.Mail: sajeevanfsi@gmail.com] Received 09 October 2013; revised 25 February 2014 The present study is an attempt to understand the composition of the gut contents of Cobia inhabiting in Indian waters. Eleven groups of marine organisms were found in the stomach of Cobia. Fishes dominated the gut contents of male cobia, whereas crabs dominated the guts of female Cobia. Results illustrated seasonal variation on the preferential food. Cobia mainly fed on the prey available in the ecosystem and this point towards the opportunistic feeding behavior of the species. Analysis on the variation of gut contents in different life history stages showed that the share of marine organisms other than fishes were more in the guts of juveniles than that of adults. [Keywords: Cobia feeding, Cobia fishery, Cobia guts contents, Seasonality in feeding] Introduction Rachycentron canadum (Linnaeus,1766) commonly known as Cobia, Black king fish, Black salmon, Ling, Lemonfish, Crabeater etc. is an esteemed table fish with high demand in the market. In India, they occur along the coastal waters of both west and east coast 1. Cobia landings are very low, however due to its high price and emerging popularity as a candidate species for culture, the species is considered as an important resource. Results of the study on the food and feeding habits of Cobia occurring in Aransas Bay 2 shared preliminary information on food and feeding behavior of Cobia. Various studies 3 17 on food and feeding habits of Cobia around the world shared some vital information on the feeding habits of this fast moving fish. However, comprehensive information on constituents of gut contents and its seasonality of occurrence in the environment and guts of Cobia is still lacking. More over, except some preliminary studies on the Cobia occurring along North West coast of India 15, knowledge on food and feeding behavior of Cobia occurring in Indian water is scanty. Hence, an attempt was made to study the food and feeding preferences of Cobia inhabiting along the North West coast of Indian EEZ. Materials and Methods Samples of Cobia collected from the vessel M.V. Matsya Nireekshani, belonging to the Fishery Survey of India, Mumbai and samples from landing centers viz. Sassoon dock and New ferry wharf at Mumbai for a period of two years from January 2008 to December 2009 were used for this study. Length, weight, sex, stomach fullness of fish and length of alimentary canal were recorded before dissecting the stomach 18. Stomachs were visually classified as gorged, full, ¾ full, ½ full, ¼ full, traces and empty based on the degree of fullness and the amount of food contained in them. Stomachs were dissected out following standard procedures 18 and the food was preserved in 5% formaldehyde for further study. Most of the stomachs were analysed in fresh condition. Three hundred and eighteen guts were examined for the study, which includes 158 male, 121female and 39 juveniles (sex not identified). Following Hyslop (1980) 19 both amount and bulkiness of the gut contents were recorded. Gut contents were identified up to group/genus/species level and grouped in to eleven categories namely, squid, cuttlefish, octopus, other molluscs, crab, penaeid shrimp, non penaeid shrimp, squilla, fish, digested matter and others. Number, volume and

1632 INDIAN J. MAR. SCI., VOL. 45, NO. 12, DECEMBER 2016 weight of each gut contents were recorded. The methods employed for the quantitative and qualitative analysis of stomach contents do not give a complete picture of dietary importance when they are used singly. However, when used in combination, such as numerical or frequency of occurrence and volumetric or gravimetric, better results were achieved 20. Index of preponderance suggested by Natarajan and Jhingran (1961) 21 is a combination of numeric/occurrence and volumetric/ gravimetric methods. Hence, index of preponderance 21 calculated following Natarajan and Jhingran (1961) 21. Month wise Index of preponderance value was calculated separately for male, female, pooled and on length group basis. Lengthwise, all fishes were grouped in to 10 cm length classes and the value for each class were estimated separately. Later, these values were compiled as juveniles (fishes below size at maturity) and adults to estimate the food preference of Cobia during these life stages. Results Composition of gut contents of male, female and pooled data calculated following index of preponderance method are presented in Table I. Fishes dominated the gut content of males with 53%, followed by crab (28%) and digested matter (9%). Dominance of crab with 33% followed by fishes 31% and squilla 12% were noticed in the gut content of females. Fishes 44%, crabs, 38% squid 8 %, others 3%, squilla 2%, Octopus 2%, digested matter 2 %, shrimp non penaeid 1% and shrimp penaeid 1%, are the major components recorded from the guts of Cobia (pooled data). Octopus, cuttle fish, others and mollusc shells occurred in the guts of Cobia, but in sparse quantity. Seasonal variation of gut contents of male, female and pooled are given in Table II. As shown in Table II, fishes dominated the gut contents of Cobia during most of the months. Occurrence of food items in different proportions during different months indicated that more than preference towards any food, seasonal availability of food item in the habitat is the deciding factor in the feed intake by Cobia. In general index of preponderance values recorded during the period indicated that Cobia feeds on the food available in their vicinity and hence the species is following opportunistic type of feeding. In general, it can be infered that seasonal variations occur on the composition of gut contents of Cobia. Table I. Composition of gut contents of Cobia Rachycentron canadum from north west coast of India. Food component Percentage of composition of gut contents in the guts Male Female Pooled Fish 53.16 31.55 44.30 Crab 27.67 34.32 37.58 Squilla 6.27 11.51 1.93 Shrimp penaeid 1.04 0.61 0.69 Shrimp non penaeid 0.12 1.73 0.58 Squid 1.07 2.99 7.79 Cuttle fish 0.004 0.55 0.65 Octopus 0.32 7.59 1.80 Other Mollusca 0.02 0.47 0.08 Digested matter 8.50 5.75 1.88 Others 1.82 3.00 3.29 Variation of major food items of male and female Cobia were noticed during April, June, July, September and November. Fishes were the dominant food item of the Cobia male during February, March, April, May, August and November. But during January, June, July, October and December crabs were dominant among the gut contents. Squids, Squilla, Shrimps penaeid and Octopus were the other dominant food items found in the guts of male Cobia. Variation of major food items of male and female Cobia were noticed during April, June, July, September and November. Fishes were the dominant food item of the Cobia male during February, March, April, May, August and November. But during January, June, July, October and December crabs were dominant among the gut contents. Squids, Squilla, Shrimps penaeid and Octopus were the other dominant food items found in the guts of male Cobia. Month wise analysis of composition of food in the guts of female Cobia showed that crabs were the dominant food item during January, April, September, October and December. Similarly, fishes dominated the gut contents during February, May and June. Squilla was the dominant food item recorded during March and August. Octopus was found more during July. Compared to male, dominance of crab among the gut content of female Cobia was noticed during the period under study. However, no specific trend on the seasonal preference towards any food item was noticed.

SAJEEVAN & KURUP: STOMACH CONTENT ANALYSIS OF COBIA, RACHYCENTRON CANADUM 1633 Table II. Month wise percentage composition of food of Rachycentron canadum Month Male Female Pooled Jan Crab(69.3), Fish(23.0), Squid(5.6) Crab(82.1), Fish(11.6), Digested matter (3.9) Crab(79.8), Fish(16), Digested matter(2.0) Feb Fish(98.8), Crab(1.0), Squid(0.1) Fish(97.4),Digested matter (1.2), Crab(1.1) Fish(98), Crab(1.2), Digested matter(0.5) Mar Fish(64.4), Squilla(33.8), Shrimp P(1.3) Squilla(55.7), Fish(24.7), Octopus(12.0) Fish(44.6), Squilla(41.6), Crab(11.7) Apr Fish(98.6), Crab(1.4),Squid(0.01) Crab(34.6),Squid(31.1),Fish(26.4), Fish(57.9), Crab(20.7),Squid(17.9) May Fish(85.3), Fish(74.8), Octopus(25.2), Shrimp P(0.4) Fish(86.4), Octopus(9.7), Crab(2.4), Crab(6.9),Octopus(3.8) June Crab(67.8),Fish(23.5), Fish(72.6), Squilla(9.9),Cuttlefish(6.6) Crab(45.6), Fish(42.3), Squilla(9.8) Squilla (8.1) July Crab(31.6),Fish(29.2), Octopus(53.9), Others(24.9),Shrimp Others(29.8), Crab(26.6), Fish(16.1) Squilla (19.6) NP(12.4) Aug Fish(82.5), Squilla Squilla(66.6), Fish(13.7), Crab(12.3) Fish(60.7), Squilla(28), Crab(6.5), (10.7),Crab(3.3) Sept Digested matter(100) Crab(80.7), Fish(11.3), Others(8.1) Crab(73.3), Fish(10.3), digested matter(9.2) Oct Crab(50.1), Fish(48.3), Crab(52.4), Fish(42.4), Digestedmatter(2.9) Fish(50.2), Crab(47.6), Shrimp P(1.8) Shrimp P(1.6) Nov Fish (59.4), Crab(40.64) Digested matter(60.8), Crab(39.2) Crab(55.6), Fish(34.2), Digested matter(10.1) Dec Crab(60.1), Fish(25.1), Shrimp P(5.8) Crab(96.1), Fish(3.8) Crab(79.9), Fish(14.8), Shrimp P(2.0) The results of index of preponderance method carried out to understand the variation on food preference of Cobia during their life history stages are presented in Table III. As furnished in Table III, fishes dominated the gut contents of juvenile (fishes below the size at maturity) and adult with 68.52% and 84.53% respectively. Percentage of crustaceans, mollusca and other food items were more in the gut of juveniles. Smaller size of these prey items can be attributed as a reason for their dominance in the guts of juveniles. Gut contents of Cobia were identified up to species/genus/ group level and grouped in to eleven groups, namely fish, crab, squilla, shrimp penaeid, shrimp non penaeid, squid, cuttlefish, octopus, other mollsca, digested matter and others. Fishes were found to be dominant among the gut contents of male during February May, August and November. In female, similar dominance was observed during February, May and June. In general, Cobia prefers fishes to any other food items. Percentage compositions of various fish species recorded from the gut contents of Cobia are furnished in Table IV. Table III. Variation in composition of food expressed in percentage of juvenile and adult of Rachycentron canadum Food component Juvenile (22.6 64 cm) Adult (65 151cm) Fish 68.52 84.43 Crab 21.22 12.86 Squilla 4.63 1.56 Shrimp penaeid 1.67 0.01 Shrimp non penaeid 1.04 0.00 Squid 1.31 0.20 Cuttle fish 0.00 0.25 Octopus 0.00 0.53 Other Mollusca 0.03 0.00 Digested matter 1.29 0.11 Others 0.30 0.05 More than twenty five genera of fishes were encountered in the guts of Cobia. Tetradontids (Puffer fish) dominated among the fishes with 91.45% followed by Mackerel (2.5%), Silver bellies (1.4) and Nemipterids (1.3%). Four varieties of crabs namely three spoted crab Portunus sanguinolentus (Herbs 1783), blue swimmer crab Portunus pelagicus (L. 1758), Charybdis feriatus

1634 INDIAN J. MAR. SCI., VOL. 45, NO. 12, DECEMBER 2016 (L. 1758) and Swimming crab Charybdis smithii MacLeay 1838 were found in the guts of Cobia. Percentage compositions of crab were 27.67, 34.32 and 37.58 among the gut contents of male Cobia, female Cobia and Cobia pooled respectively. Month wise, crab dominated the gut contents of male Cobia during January, June, July and December. In the case of female, crabs were the dominant food item during January, April, September and December. Percentage of occurrence of crab in the guts of juveniles was more than that of adults. Table IV. Percentage composition of fishes in the gut contents of Rachycentron canadum (pooled) Fish components % of compo sition Fish components % of compo sition Tetradontids 91.45 Cynoglossuss spp. 0.08 Rastrelliger 2.57 Sphyraena spp. 0.04 kanagurta Leiognathids 1.41 Stolephorus spp. 0.02 Nemipterus spp. 1.30 Megalaspis 0.01 cordyla Decapterus spp. 0.88 Platycephalus spp. 0.01 Congresox 0.71 Harpodon 0.01 nehereus Therapon jarbua 0.20 Sardinella spp. 0.01 Acropoma sp. 0.20 Trichiurus sp. 0.01 Other carangids 0.18 Epinephelus 0.004 diacanthus Elasmobranchs 0.17 Sciaenids 0.001 Saurida spp. 0.15 Ambassis spp. 0.0003 Priacanthus spp. 0.14 Alectis spp. 0.0002 Cynoglossuss spp. 0.08 Others 0.44 Squilla occurred 6.27% and 11.51% of gut contents of male and female Cobia respectively. Month wise, squilla was the main food item of female Cobia during March and August, but they were totally absent during September December. Similarly, they were completely absent in the guts of male Cobia during September February and April May. Squilla occurred 4.63% of the gut contents of juvenile, but they occupied only 1.56% of gut contents in adults. Commercially important penaeid shrimps like Indian white shrimp Fenneropenaeus indicus (H. Milne Edwards 1837), Giant tiger prawn Penaeus monodon Fabricius 1798, Banana shrimp Fenneropenaeus merguiensis (De Man 1888), Kadal shrimp Metapenaeus dobsoni (Miers 1878), Speckled shrimp Metapenaeus monoceros (Fabricius 1798), Jinga shrimp Metapenaeus affinis (H. Milne Edwards 1837), Coastal mud shrimp Solenocera crassicornis (H. Milne Edwards 1837) and ridge back shrimp Solenocera choprai Nataraj 1945 were encountered in the gut contents of Cobia. On an average, penaeid shrimps occupied 1.04 and 0.70 percentages of gut contents of male and female Cobia respectively. Penaeid shrimps contributed to 1.67% of gut contents of juvenile, but their share was only 0.01% among the gut contents of adults. Month wise, maximum occurrence of penaeid shrimps were found during December (5.78%) followed by June (2.17) in both the sexes. Non penaeid shrimps occupied 0.02 and 1.73 percentages of gut contents of male and female Cobia respectively. Commercially important non penaeid shrimps like spider prawn Nematopalaemon tenuipes (Henderson 1893), hunter shrimp Exhippolysmata ensirostris (Kemp 1914),planktonic shrimp Acetes indicus H. Milne Edwards 1830, Acetes johni Nataraj 1949,alamang shrimp Acetes sibogae Hansen 1919 and tsivakihini paste shrimp Acetes erythraeus Nobili 1905 were found in the gut contents of Cobia. They occurred in 1.04% of gut contents of juvenile Cobia but were totally absent in the guts of adults. Passive type movement of non penaeid shrimps may be the reason behind this disparity; moreover, this is an indication of the more active preying of the adults. Squid occupied 1.07 and 3.0% of gut contents of male and female Cobia respectively. Indian squid Loligo duvauceli Orbigny 1848, Sioboga squid Doryteuthis sibogae Adam 1954 and Loliolus investigatoris Goodrich 1896 are the squids found in the guts of Cobia. Squids contributed to 1.31% of gut contents of juveniles, but were found only 0.20 % in the guts of adult Cobia. Month wise, squids were completely absent in the guts of male Cobia during July to November. In the case of female Cobia, they were totally absent in the gut contents during August January. Pharao cuttlefish Sepia pharaonis Ehrenberg 1831, Needle cuttlefish Sepia aculeate Van Hasselt 1835, Golden cuttlefish Sepia elleptica Hoyle 1885 and spineless cuttlefish Sepiella inermis (Van Hasselt 1835) were the cuttlefishes found in the guts of Cobia.

SAJEEVAN & KURUP: STOMACH CONTENT ANALYSIS OF COBIA, RACHYCENTRON CANADUM 1635 They were almost absent in the guts of male and contributed 0.55% of gut contents of female Cobia. Absence of cuttlefishes in the gut contents of juveniles was also noticed during the present study. Meanwhile, cuttlefishes occupied 0.25% of gut contents of adults. Month wise, except a 0.06% contribution noted during February, cuttlefishes were completely absent in the guts of male Cobia. They were found in the guts of female during February (0.08%) and June (6.55%) but were absent during the rest of the period. Octopus contributed to 0.32 and 7.59% of gut contents of male and female Cobia respectively. They were completely absent in the guts of juveniles and occupied 0.25% of gut contents of adults. Month wise, octopus were found only during February (0.02%) and May (3.81%) in the guts of male Cobia. In the case of females, octopus was the dominant food item during July (53.90%). They were also found in the guts of female Cobia during February July period. Molluscan shells found in the guts of Cobia form this category of food items. They contributed to 0.47% and 0.08% of gut contents of male and female Cobia respectively. They were present only in the guts of juveniles and were absent in the guts of adults. Unidentifiable digested matters were pooled in to this category of digested matter. They occupied 8.5 and 5.7 percentage of gut contents of male and female Cobia respectively. During September all the gut samples of male Cobia were full of digested matter, similarly 60.83% of gut contents of female during November was also characterised by digested matter. They were recorded from both adult and juvenile guts. Occurrence of materials like lemon, wood piece, sand particle etc in the guts of Cobia was noticed sporadically. These items were pooled together as others. This group occupied 2 3% of the gut contents of Cobia. Discussion Cobia feed on a variety of prey items that are available in the vicinity and are considered as voracious feeder. They are carnivorous and feed extensively on fishes, crustaceans, cephalopods, and benthic invertebrates. Major food items reported by different authors from different geographical locations are furnished in Table. V. As shown in Table V the preferential food of Cobia varied from region to region. Geographical differences in the availability of prey items and resultant differences in the Cobia diets 16 may be the reason for this variance. They have been called as crab eaters in some parts of Australia due to the presence of large amount of crabs in their diet 22 23. But results of present study indicate that fishes are the major food items of cobia inhabiting in Indian waters. Findings of Somavnshi et al. (2000) 15, and Franks et al (1996) 24 are in agreement with the results of present study. Table V. Preferential food items of Rachycentron canadum reported by various authors from different localities Major food items Crab and Penaeid shrimp No. of Area of observations study Texas Gulf coast Crustaceans Western Indian Ocean Elasmobranches and Portunid crab Fish (Anchoa sp.) Crustaceans (Portunid crabs) North Carolina Northern Gulf of Mexico Northern Gulf of Mexico Fishes 100 Northern Gulf of Mexico Fishes 30 North west coast of India Crab (Portunid crab) Author/s Knapp(1951) Darracott (1977) Smith (1995) Franks et al. (1996) Meyer and Franks (1996) Franks et al. (1999) Somvanshi et al. (2000) 78 Lower Arendt et al.(2001) Chesapeake Bay Present study Fishes and crabs 318 North west coast of India Study on the feeding habits of Cobia occurring in western Indian ocean 8 reported presence of undamaged crustaceans in the guts of Cobia.Presence of undamaged prey items in the guts observed during the present study manifest that Cobia often engulf the prey and exhibits feeding absenteeism 8. Large amount of benthic, demersal and pelagic fishes recorded from the guts of Cobia indicated that Cobia feed not only from near the bottom but also in the water column.

1636 INDIAN J. MAR. SCI., VOL. 45, NO. 12, DECEMBER 2016 Study on the food habits of Cobia occurring in Texas Gulf coast 4 also reported a similar result and hence are in agreement with the results of the present study. As far as the north west coast of India is concerned, Cobia mainly fed on puffer fish (92.1%) followed by cephalopods (2.5%) 15. Present study showed that 42.72% of gut contents is occupied by puffer fishes. Fish as a whole contributed 44.30% of the gut contents followed by 33.58% of crabs. Crustaceans were reported to be occupying 70% and 100% of guts examined by Miles (1949) 2 and Darracot (1977) 8 respectively, hence they are of the opinion that crabs are the major food item of Cobia 2, 8. In the present study crabs (33%) constituted the major food item of the female Cobia. Meyer and Franks (1996) 14 opined that there is no remarkable difference between the diets of male and female Cobia. Variation in percentage composition of food items in the guts of male and female Cobia was noticed during the present study, as the major constituent of male gut content was fish, where as crab was the major food content found in the gut of female Cobia. Conclusion The present study is an attempt to understand the food and feeding behavior of Cobia occurring in Indian water. Results of the present study illustrated the composition of gut contents and seasonal variations of the occurrence of prey items in the guts of Cobia. Results of the study indicated that, Cobia generally feeds on the prey available in the environment and is opportunistic in feeding behavior. A difference in the percentage of occurrence of gut contents in male and female Cobia was a major finding of the present study. In general Cobia male prefer fishes than crabs, where as female Cobia preferred crabs over fishes. Dominance of fishes than the crustaceans and mollusca in the gut content of adults indicate that adults prefer active prey items than the passive prey items. Acknowledgement Authors are grateful to Prof. (Dr.) A. Ramachandran Director, School of Industrial Fisheries for granting permission and providing necessary facilities for the successful conduct of the research work. Authors are thankful to Dr. K. Vijayakumaran, Director General, Fishery survey of India, Mumbai; Dr, V.S Somvanshi, Former Director General, Fishery Survey of India, Mumbai for the facilities provided. References 1 Sajeevan, M.K. Systematics, life history traits, abundance and stock assessment of Cobia Rachycentron canadum (Linnaeus, 1766) occurring in Indian waters with special reference to the northwest coast of India. Ph.D. Thesis, Cochin University of Science and Technology, Kochi. 2011. 2 Miles, D. W., A study of the food habits of the fishes of the Aransas Bay area. M.S. thesis. 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