Effects of stocking density on blood chemistry and amino enzymatic activity of juvenile Nile tilapia Oreochromis niloticus (Linnaeus, 1758) in hyperosmotic rearing condition

Nile tilapia Oreochromis niloticus, a euryhaline species, is a good candidate for culture in estuarine areas in the Philippine archipelago. Thus, the effects of stocking density on plasma cortisol, blood glucose, plasma aspartate transaminase (AST), and plasma alanine transaminase (ALT) were determined. The group of juvenile Nile tilapia O. niloticus (14.67 ± 0.12 cm TL and 44.57 ± 0.48 g W) was subjected to three different stocking densities (6, 12 & 24/60 L) for 14 days in 15‰ rearing condition. The experiment was composed of three treatments with triplicated groups arranged in a completely randomized design (CRD). Highest stocking density affected the plasma cortisol, blood glucose, plasma AST and ALT of Nile tilapia by increasing its concentration level in the blood. These manifestations suggest that overcrowding in Nile tilapia affects the physiological function through hormonal secretion, glucose utilization, and protein catabolism of the species.