Secondary stress responses in Indian major carps Labeo rohita (Hamilton) , Catla catla (Hamilton) and Cirrhinus mrigala (Hamilton) fry to increasing packing densities

Glycogen content and metabolic enzyme activities viz. lactate dehydrogenase (LDH), malate dehydrogenase (MDH), aspartate amino transferase (AST) and alanine amino transferase (ALT) in Indian major carps, Labeo rohita , Catla catla and Cirrhinus mrigala , were investigated after a 6 h transportation trial to compare the species‐specific variation and the effect of increased packing density on the metabolism. Fish (45±5 mm, 0.5±0.1 g) were packed in three densities (100, 150 and 200 L −1 ) for the experiment, and 12 specimens of each species were randomly sampled from all the treatments at the end of transportation. The glycogen content of L. rohita ingerlings decreased significantly ( P <0.05) with increasing packing density. The activities of enzymes LDH, MDH, AST and ALT showed a rising trend with increasing packing density in all the three species. Species‐specific differences were observed in various tested parameters at the lowest packing density (100 fry L −1 ). Alanine amino transferase and LDH activities were significantly ( P <0.05) lower in C. mrigala as compared with the other two species. However, glycogen reserves and MDH activity were not significantly different ( P >0.05) among the species. The present study reveals that the optimum packing density for Indian major carp fry (100 fry L −1 ) for transportation up to 6 h and metabolic regimes are species specific during transportation.