Indian Journal of Marine Sciences Vol. 28, September 1999, pp. 307-311 Food habits and feeding intensity of finlet scad Atule mate (Te1eostei) off Gulf of Mannar, southeast coast of India S.David Kingston, V.K.Venkatararnani & K.Venkataramanujam Fisheries College and Research Institute, Tamil Nadu Veterinary and Animal Sciences University, Tuticorin - 628 008, Tamil Nadu,India Received 8 September 1997; revised 16 March 1999 Atule mate exhibits two types of feeding patterns, the juveniles feeding mainly on crustaceans and the adults exclusively on fishes. Low intensity of feeding was observed in juveniles, males and females. Juveniles had high diet breadth (2.86) when compared to the males (1.86) and females (2.10). The overlap studies showed clustering of high overlaps in the younger and older length groups. The dendrogram of the diet at various length groups showed two principal clusters, one at 91-150 mm (TL) length group and another at 151-280 mm (TL) length group. As per the cluster analysis two types of food patterns are evident in this species. < Knowledge on the food and feeding habits is essential to have an idea on growth, distribution and general ecology of the fish. Changes in the food spectrum during different seasons help us to study the migratory patterns of the fish. It also helps in the selection of suitable species for aquaculture. Studies on the food and feeding habits of carangid fishes in the Gulf of Mannar region are limited l. 4 In the present study, a detailed analysis on the food and feeding intensity of one finlet scad,atule mate(cuvier, I 833) has been attempted. Studies on these aspects have not been made so far in this species from the Gulf of Mannar region. This species forms an important fishery along the coast of Gulf of mannar and has got good potential for aquaculture in marine environment, as the matured specimens, eggs and larvae are also available throughout the year. Materials and Methods The material for the present study were collected from the trawl fish landing centres (Vembar, Tuticorin and Tiruchendur) along the Gulf of Mannar (between lat.8s ;long.79 and lat.7s;long.77s). A total of 530 specimens of Atule mate (230 males, 210 females and 90 juveniles) were examined for one year (January 1992 to December 1992). All specimens were measured accurately, their total length (TL) and sex were noted. The stomach was preserved in 4% formaldehyde for further study. In order to ascertain the feeding intensity during various months, the degree of fullness of the stomach was noted. The stomach was designated as 'gorged' when it was distented with food, with its wall thin and transparrent. The stomach was considered as 'full' when it was filled with food, its wall being comparatively thin and intact. Similarly they were classified as '3/4 full', '112 full' and '1/4 full' depending upon their relative fullness and the space occupied by the stomach in the body cavity. A stomach was designated and termed as 'trace' when its content occupied less than one fourth of the capacity of the full stomach. Shrunken stomachs containing mucus were considered as empty and were not evaluated. The food items in the stomach were identified up to generic level depending on their digested state. The unidentifiable (partly digested) fishes in the gut were included in the category 'fish '. Adults were sexed and their stomach contents were analysed separately. In the present study, specimens without gonads (90-140 mm) were considered as juveniles. The volume displacement method followed by McEachran et al. 5 was used to quantify the gut contents. The diet breadth, an index which varies with the proportion of components in the stomach was ca\culated 6 separately for juveniles, males and females using the formula" B = I/Pij, where B = diet breadth and Pij = the proportion of resource in each category.low breadth indicates clumping of the diet components and high value indicates equidistributio'l of various food components.
308 INDIAN 1. MAR. SCI., VOL. 28, SEPTEMBER 1999 To study the changes in the food pattern during the growth of the species, the diet was analysed at various length frequency levels. For this study, 10 mm size frequency was chosen. The diet overlap between different length frequencies was calculated based on the formula 7 : S = 100 [P-(Pxi-Pyi)] where Pxi = proportion of ith category in 'x' length group and Pyi = proportion of ith category in 'y' length group. Cluster analysis was also used to study the similarity between the diets of various length groups. The Basic program of Ludwig & Reynolds 8 was used for this analysis. A dendrogram had been drawn to depict the principal clusters. Results and Discussion Food composition. The food components, were grouped into 8 categories namely clupeids, fish, crustaceans, leiognathids, sciaenids, molluscan, carangide and algal in the order of abundance (Table I). Table I-Percentage composition of food items and diet breadth in 1uveniles, males and females of A. mate Food items Clupeids Fish Crustacean Leiognathids Sciaenids Molluscan Carangids Algal Diet breadth 1uveniles (%) 27.21 57.70 9.84 5.25 2.86 Males(%) Femalcs(%) 73.52 66.81 10.96 19.11 7.04 3. 12 3.37 5.62 4.00 2.50 0.66 0.71 0.32 0.62 0. 13 1.51 1.86 2.10 Among fishes, only bony fishes were recorded in the gut contents of A. mate. The juvenile bony fishes include, c1upeids, leiognathids, sciaenids and carangids. Among c1upeids Stolepho1"Us spp., Thryssa spp. and Setipinna spp. were recorded. The group 'fish ' include unidentified fishes and fish. Among crustaceans, shrimps, crabs and their, exoskeleton were encountered. Broken shells of bivalves and gastropods constituted a minor share among molluscan. Algal were also recorded in trace quantities in the gut of A. mare. Diet breadth a/juveniles and adults The percentage composition of food items and the diet breadth of juveniles, males and females of A. mate (Table I) showed that crustacean formed the main food item for juveniles (57.70%). Clupeid fishes dominated in the gut contents of males (73.52%) and females (66.81 %). The juveniles had high diet breadth (2.86) whereas males had the least (1.86). The diet breadth of females was 2.10. Thus it was evident that the juveniles fed on a variety of food items and its food spectrum narrowed down to a few varieties in adults. The monthly percentage composition of various food items (Table 2) showed that clupeid fishes and fish were present in the gut contents throughout the year. High percentage of c1upeids during September (67.63%) and October (99.04%) showed that the fish fed largely on clupeids during these months. The subsequent reduction of c1upeid diet during November (45,78%) and December (31.25%) may be due to the monsoon season during which time, the food intake might have been less owing to the reproductive activity of A. mate. This is in confirmation with the more occurrence of matured males and females during these months. Generally the c1upeids showed a trend Table 2-Seasonal Percentage composition of food items in A. mate Food items 1an'92 Feb'92 Mar'92 Apr'92 May'92 1un'92 1ul'92 Aug'92 Sep'92 Oct'92 Nov'92 Dec'92 Clupeids 50.57 48.58 54.43 47.31 28.57 46.76 50.27 63.52 67.63 99.04 45.7X 31.25 Fish 40.23 47.77 14. 18 17.54 60.71 20.86 29.89 11.37 15.20 O.l)() 14.46 45.83 Crustacean 2.83 14.68 21.29 21.58 14.40 2.95 0.45 38.55 20.84 Leiognathids 3.45. 6.33 8.97 10.72 5.40 5.44 22.16 16.72 Scia\!nids 8.86 5.40 Molluscan 4.60 0.82 1.52 1.63 1.21 2.0S Carangids 3.26 Algal 1.15
DAVID KINGSTON et at.: FOOD AND FEEDING OF ATULE MATE 309... from January to October except during May (28.57%). Probably the fish would have consumed more of c1upeids in this month and the same could have been partially digested, hence higher percentage of fish registered in the month of May. In this month fish were recorded to a maximum of 60.71%. Crustacean formed 38.55% during November and molluscan formed 4.60% during January. Food habits in relation to length group The diet pattern at various length groups (Fig.!) showed that there was a gradual shift in diet from the lower length group to the higher length group. The critical change was observed in the 141-150 mm length group. Crustacean dominated in the gut contents of A. mate from 91 mm to 141 mm (TL) and from 151 rnm to 280 mm, c1upeid contribution in the diet was more with a reduction of crustacean (Fig. 1 ). The overlap of stomach contents between the various length groups was calculated and given in Table 3. Out of 171 combinations, 84 (49.10%) showed high overlaps (>0.66) and 87 (50.90%) showed low overlaps ( < 0.33). There was a clustering of high overlaps in the earlier length groups and older length groups. The dendrogram of the diet during various length groups (Fig.2) showed two principal clusters formed in the 91-150 mm length groups and 151-280 mm length groups. The two clusters formed clearly reflects two types of food patterns in A. mate. Feeding intensity The intensity of feeding in males, females and juveniles was given in Fig.3. In general, a low feeding intensity was observed in this species. Such low feeding intensity has also been recorded in other species of carangids like MegaLaspis cordyla 9 and ALectis indicus lo In juveniles a high percentage of Algae Molluscan Fish Crustacean :: Lelognathids Carangids Clupeids Sciaenids w C> ~ I- Z W 50 u 0::: W a. LENGTH Fig. I-Histogram showing the diet components of A.mate at various length groups
310 INDIAN J. MAR. SCI., VOL. 28, SEPTEMBER 1999 'trace' (56.52) and 'empty' (34.78) stomachs were recorded and 'gorged', 'full' and '3/4 full' stomachs were absent. In males and females, 'trace' and 'empty' stomachs were more. The more occurrence of 'trace' and 'empty' stomachs also confirm the piscivorous feeding nature of the fish food which has more calorific value as explained by Longhurst ll According to him, species having fish as their important food item, the intake will be less owing to the high calorific value of the diet. Length 101 III 121 131 141 91-100 0.75 0.76 0.78 0.89 0.88 101-110 0.99 0.97 0.86 0.80 111-120 0.98 0.87 0.81 121-130 0.89 0.83 131-140 0.93 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 251-260 261-270 1'1 J 0 5 Table 3-Diet overlap between various length groups in A. mate (Underlined numbers indicate high overlaps) Length 151 161 171 181 0.41 0.20 0.39 0.27 0.31 0.07 0.16 0.32 0.08 0.18 0.34 0.10 0.19 0.20 0.41 0.20 0.30 0.27 0.41 0.25 0.29 0.27 0.64 0.85 0.86 0.67 0.64 0.87 J The presence of" more fish food in the stomach reveals that this fish is piscivurous in nature and the presence of more clupeids confirms that this species is mainly a pelagic feeder. Similar feeding nature has also been reported in other carangid fi shes like Decapterus dayi3 and Megalaspis cordylct". The change in the food pattern in the higher length groups as observed presently has also been observed in other carangids like D. dayp and M. cordylt/. According to Sreenivasan 9 such change can be related 191 0.42 0.18 0.20 0.31 0.30 0.77 0.69 0.89 0.77 201 0.23 0.03 0.04 0.06 0.72 0.63 0.84 0.86 0.73 100 211 0.25 0.10 0. 11 0.13 0.24 0.23 0.74 0.67 0.79 0.74 0.80 0.72 221 23 1 24 1 25 1 261 271 0.28 0.2 i 0.10 0.1 i 0.32 0.25 0.05 0.07 0.04 0.00 0.08 0.00 0.06 0.08 0.05 0.01 0.0<) D.O I 0.08 0.10 0.07 0.03 0. 11 0.03 0.19 0.21 0.10 0. 11 0.22 0. 14 0.20 0.21 0.10 0. 11 0.22 0.13 0.74 0.76 0.69 Q.69 0.77 0.69 '0.69 0.68 0.57 0.58 0.68 0. 60 0.89 0.82 0.71 0.72 0.92 0. 84 0.85 0.80 0.83 0.83 0.83 0.77 0.78 0.76 0.63 0.61 0.82 0.76 0.93 0.80 0. 86 0.88 0.88 0.97 0.74 0. 89 0.69 0. 65 0.77 0.69 0.83 0.80 0.81 0.94 0.90 0.77 0.74 0.85 0.77 0.88 0.75 0.73 0.76 0.78 0.89 0.2 0 1 Length groups > I- Vi :z: I Z :; 50 z o lj..... 00 0 0 DO FEM MAL...... JUV 0 Emp ty 0 Trace ~ J;: Full!z Full 0 1;: Full Full 0 Gorged Fig.2-Dendrogram showing the percentage dissimilarity of gut contents at various length groups in A. mate Fig.3-Figure showing the intensi ty of feeding in Juven iles, maies and females in A. mate
DA VID KINGSTON e/ al.: FOOD AND FEEDING OF A TULE MATE 311 to the area of filtration formed by the gill apparatu~ as 12 demonstrated by Magnuson & Hettz. The dominance of crustacean in the lower length groups shows that the juveniles resort to bottom feeding nature and the presence of more pelagic fishes in the adults show that they confine to pelagic region. Thus the animal experiences a change in habitat as it grows. Moreover the presence of carangid fishes in the diet shows that this species is cannibalistic in feeding habit at times. The fusiform body of this species helps to prey upon fast moving organisms both in juveniles as well as in adults. However the high diet breadth in the juveniles shows that their food spectrum is high when compared to the adults. This is in confirmation with the views expressed by Eggleston 13 and Rao & Rao 14 in nemipterid fishes. References I Chacko P I, Proc Indian Acad Sci, 29 (1949) 83. 2 Kuthalingarn M D K, J Madras Ulliv. 29 (1959) 79. 3 Sreenivasan P V, Indian J Fish, 21 (1979) 76. 4 Venkatararnani V K & Natarajan P. Matsya. 14 (1988) 53. 5 McEachran J D, Noesch D F & Musick J A. Mar Bioi. 35 (1976) 301. 6 Levins R, Evolution in changing environments, (Princeton Univ. Press, USA) 1968, pp. 120. 7 SchoenerTW, Ecology, 51 (1970)408. 8 Ludwig J A & Reynolds J F, Statistical ecology, a primer 011 me/hod and computing, (Wiley Interscience.New York) 1988, pp.329. ' 9 Sreenivasan P V,Indian J Fish, 21 (1974) 76. 10 Venkatararnani V K, Sundararaj V &. Gopalakrishnan p, 1. Aquatic Organisms, 2 (1989) 80. II Longhurst A R, J Animal Ecol, 26 ( 1957) 369. 12 Magnuson J J & Hettz J G, Fish Bull. 69 (1971) 361. 13 Eggleston D, J Mar Bioi Ass India, 14 (1972) 357. 14 Rao D M & Rao K, J Mar Bioi Ass India. 33 (1991) 335. r