Influence of incubation temperature on Oreochromis niloticus (L.) eggs and fry : II. Survival, growth and feeding of fry developing solely on their yolk reserves

Abstract

The consequence of constant water temperature of 17, 20, 24, 28, 30 and 34.5°C on the survival, growth and first feeding capabilities of O. niloticus hatchlings developing solely on their yolk reserves were investigated. The survival times (ST 50) of fry were temperature-dependent and ranged from 2.5 days post-hatching at 34.5 to 18.5 days at 20°C. With the exception of 20 and 34.5°C, mass mortality of fry coincided with the onset of yolk exhaustion. The mean upper and lower median tolerance limits (with 95% confidence limits) from hatching to first feeding stage were 32.1°C (31.9–32.2°C) and 21.8°C (21.4–22.3°C), respectively. Optimal survival to first feeding (>90%) during this period occurred at 28–30°C. Incubation temperature influenced the weight of the body and yolk reserves of emergent fry; fry hatching with a lower mean dry body weight contained greater yolk reserves. Maximum mean body weight and minimum mean yolk weight of emergent fry occurred at 30°C. The growth rate (SGR, %/day) of fry was temperature-dependent. Maximum growth rate occurred between days 3 and 6 at 28 and 30°C and maximum body weights were attained by 18, 9 and 6 days at 24, 28 and 30°C, respectively. The gross yolk utilization efficiency between hatching and maximum dry body weight was temperature-dependent between 24 and 30°C and ranged between 55.4% and 61.7%. At higher rearing temperatures feeding commenced earlier. Onset of feeding and point-of-no-return occurred at 8, 5 and 4 days and 23, 20 and 18 days, respectively, at 24, 28 and 30°C.