Stocking density is an important factor in cage aquaculture of finfish. Effects of high stocking density (35 fish cubic m(-1)) on a range of biochemical and immunological parameters in Asian seabass reared in open sea floating net cages were compared to fish held in relatively low density (15 fish cubic m(-1)). The results revealed that chronic stress due to high stocking density induced variations in most of the parameters studied as evidenced by increased cortisol and glucose levels and decreased activity of lysozyme, myeloperoxidase and complement. Production of reactive oxygen species, total leucocyte count and total serum protein were also decreased, whereas anti-protease, alkaline phosphatase and acid phosphatase activities were increased in high stocking-density group when compared to low stocking-density group. Effects of chronic stress due to high stocking density were discussed in relation to variations in these parameters.

Sodium cyanide, is highly contaminating aquatic ecosystems as a toxic pollutant, was investigated in the present study for acute toxicity on freshwater fish Labeo rohita. The toxicity tests were conducted by static renewal bioassay method on the juveniles of fish was evaluated. The LC 50 value of sodium cyanide to Labeo rohita was found out to be 320 µg l-1. One third (106 µg l-1) and one fifth (64 µg l-1) of the LC 50 value was selected for sublethal studies. Behavioural patterns and oxygen consumption were observed in both (1/3 rd and 1/5 th) sublethal concentrations (1, 5, 10 and 15 days). Sodium cyanide is highly toxic to the animal tested. Fish behaved irregular, erratic, and dartic movements, by followed hyperexcitability, loss of balance, finally settles to the bottom of the test chamber. A decrease in oxygen consumption was observed in 1/3rd (11.62% and-4.52%) and 1/5 th (9.11% and-2.82%) sublethal concentrations. Fish under sublethal concentration were found to be under stress but not fatal.

No abstract