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Effects of weaning age on survival and growth factors of <i>Heterotis niloticus</i> (Cuvier, 1829) larvae
Abstract
Heterotis niloticus is an important fishery resource because of its individual large size and high commercial value. There is population decline due to habitat degradation and high fishing effort. The rearing of H. niloticus larvae, particularly the weaning phase, is one of the major problems for the successful farming of this species. This research aimed at investigating the age at weaning of H. niloticus larvae and its effects on survival and growth rates. Two independent series of weaning experiments were conducted under natural conditions. The first experiment (early weaning stage) included four treatments, namely: T1 (control) = larvae fed only Artemia nauplii, and T2, T3, T4 corresponding to three weaning ages of 11, 13, and 15 days after hatch (DAH), respectively. The second experiment (late weaning) included three treatments: T1 (control) =
larvae fed only Artemia nauplii, and T2, T3 corresponding to two weaning ages, 24 and 26 DAH, respectively. For the early weaning experiment, eight days (9 DAH -16 DAH) of larval rearing resulted in low survival (14.7%, 10.0%, and 14.1%) and low SGR (6.56%.d-1, 6.55%.d-1, and 7.68 %.d-1) for the 11 DAH, 13 DAH, and 15 DAH larvae, respectively. The survival (65.29%) and SGR (12.55%.d-1) from Artemia fed larvae were the
highest and significantly different (p<0.05) from those of weaned larvae. On the contrary, the late weaning (larvae weaned at 24 and 26 DAH) exhibited some positive responses to the shift to artificial diet. After twelve
days of rearing, the survivals (45% and 50.83% for 24 DAH and 26 DAH, respectively) and SGR (8.90%.d-1 and 9.95% d-1 for 24 DAH and 26 DAH, respectively) were improved, suggesting that the weaning of H. niloticus larvae should begin approximately from 24-26 DAH. With respect to the rearing conditions and food types, additional research should seek to determine the appropriate age of switch from live food to an artificial diet to improve survival and growth rates of H. niloticus larvae.
Keywords: Aquaculture, artificial diet, Heterotis niloticus, larvae, survival, weaning age.
larvae fed only Artemia nauplii, and T2, T3 corresponding to two weaning ages, 24 and 26 DAH, respectively. For the early weaning experiment, eight days (9 DAH -16 DAH) of larval rearing resulted in low survival (14.7%, 10.0%, and 14.1%) and low SGR (6.56%.d-1, 6.55%.d-1, and 7.68 %.d-1) for the 11 DAH, 13 DAH, and 15 DAH larvae, respectively. The survival (65.29%) and SGR (12.55%.d-1) from Artemia fed larvae were the
highest and significantly different (p<0.05) from those of weaned larvae. On the contrary, the late weaning (larvae weaned at 24 and 26 DAH) exhibited some positive responses to the shift to artificial diet. After twelve
days of rearing, the survivals (45% and 50.83% for 24 DAH and 26 DAH, respectively) and SGR (8.90%.d-1 and 9.95% d-1 for 24 DAH and 26 DAH, respectively) were improved, suggesting that the weaning of H. niloticus larvae should begin approximately from 24-26 DAH. With respect to the rearing conditions and food types, additional research should seek to determine the appropriate age of switch from live food to an artificial diet to improve survival and growth rates of H. niloticus larvae.
Keywords: Aquaculture, artificial diet, Heterotis niloticus, larvae, survival, weaning age.
