Pattern of physicochemical changes in the water during hatching of Indian carp eggs in a Chinese hatchery system

Physicochemical changes in the water were monitored at different hours of embryonic and larval development of Indian carp (Cirrhinus mrigala) eggs in a Chinese hatchery system with 75–85% hatching success. At a water temperature of 29.3°C, mass hatching of the embryos started at about 11–12 h after fertilization and was completed within 4 h. The amount of dissolved oxygen and chemical oxygen demand ranged between 4.8 and 9.63 mg l^?1 and 16.5 and 185.0 mg l^?1, respectively. A marked rise in the concentration of bicarbonate and total hardness of the water after egg transfer into hatching tanks was perhaps due to liberation of Ca²⁺ and Mg²⁺ from the egg mass. A sharp decline in phosphate content during hatching was associated with the building of bones, while the ammonia level was greatly increased due to a high rate of nitrogenous excretion during hatching.