Effect of prolonged ammonia toxicity on fertilized eggs, hatchability and size of newly hatched larvae of Nile tilapia, Oreochromis niloticus

The present study showed that a lethal dose of unionized ammonia (NH3-N/l) ranged from 0.06 to 1.5 mg/l. LC50 value 96 h of unionized ammonia was recorded as 0.8 mg/l. The mortality rate reached 100% after exposure to 1.5 mg. Fertilization and hatching rates were more affected after exposure to high concentrations of ammonia (0.5–0.6 mg/l) (p < 0.05). The number of deformed eggs increased with increasing ammonia concentration. However, the lowest value of deformed eggs was less affected at low doses that ranged from 0.05 to 0.25 mg NH3-N/l. Effects of high doses of ammonia (0.5–0.6 mg/l) were more pronounced on weights of larvae than those on lengths. There were no significant differences recorded in weight of larvae exposed to low doses of ammonia and those of control group (p > 0.05). The lowest value of survival rate was recorded after 60 days in groups of larvae that were exposed to high doses of unionized ammonia. Clinical signs such as malformation in yolk sac, spine curvature and darkening in eyes as well as skin were more pronounced after exposure to high doses of ammonia for a period of 60 days post-hatching.