FOOD TYPE PREFERENCE AND SIZE IN RELATION TO MOUTH GAPE OF LARVAL STAGES OF CLIMBING PERCH ANABAS TESTUDINEUSKhushvir Singh, S. Munilkumar, Narottam Prasad Sahu and Arabinda Das
Low survival during early larval stages is one of the bottle necks in the successful seed production of many fish species. Many extrinsic and intrinsic factors may be responsible for low survival rates, but the most critical factor influencing larval survival is probably the availability of right kind and size of live food in appropriate densities. Live foods are still superior to the best artificial diets in terms of larval survival and growth. In this experiment, we studied the type of prey and size preference of two important freshwater live foods, Brachionus calyciflorus and Moina micrura in relation to the mouth gape of A. testudineus larvae of different age groups. The prey selectivity index was calculated for 3, 4, 6, 8, 10, 13 and 15 days old larvae based on the changes of prey density in water. The 3-8 days old larvae showed preference for B. calyciflorus (143±8μ); the 15 days old larvae showed preference for M. micrura (221±11μ) and those 10-13 days old larvae showed random selection for both. The selection of B. calyciflorus was found positive when the size appears at 22.75% of the larval mouth gape or above at 90º angle of jaws. Similarly, highest selection of M. micrura by the larvae was found at 21.81% of the mouth gape. When prey size to larval mouth gape for B. calyciflorus appeared below 22.75%, random selections occur and at 14.11% negative selection occurs; whereas for M. micrura random selections occur when its size appeared above 21.81% and negative selections occur above 28.01% of mouth gape. These findings indicated a prey size dependent selection by the larvae. Therefore, 1:5 to 1:4 ratio of prey size to larval mouth gape at 90º angles of jaws was suggested for larval feeding of A. testudineus.
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