Light conditions for commercial hatching success in Nile tilapia (Oreochromis niloticus)

Abstract Light plays an important role in the development of biological rhythms in fish. Previous studies on tilapia has revealed that spawning rhythms and juvenile growth are significantly influenced by photoperiod. However, the effect of light conditions on the hatching rhythms are unexamined thus far. Therefore, the aim of this study was to investigate the impact of the light conditions on the hatching in Nile tilapia. To this end, the central composite experimental design and response surface methodology were utilized to study the combined effects of photoperiod and light intensity on the hatching rate as well as the growth of early fry. Based upon the results of trial tests, regimes of photoperiod and light intensity ranged from 2 to 24 h and from 100 to 2000 lx (1.26 to 25.20 μmol m −2  s −1 ), respectively. The results demonstrated that within the factorial space developmental rhythms at the egg stage were significantly influenced by light conditions, signaling that the timing of hatching in Nile tilapia could be regulated by ambient light conditions. The more unsuitable the light conditions, the longer the eggs took to hatching (or the stronger inhibitory effect of light conditions on hatching), underlining the importance and necessity of affording optimized photoenvironment during commercial incubation as well as early fry development of tilapia. The effect of light intensity was greater than that of photoperiod during early ontogeny. The interaction between photoperiod and light intensity was found to be present, implying that the effect of only photoperiod upon reproduction and growth of Nile tilapia in all previous studies might be modified. Relationship of hatching to light conditions also could be reliably modelled. The optimal photoperiod/intensity combinations, 13.45 h/1020 lx (12.85 μmol m −2  s −1 ), were derived via model optimization, the optimality of which had been verified under commercial hatching conditions. These findings emphasize that the light conditions are essential and should be taken into account in optimizing the protocols of the commercial incubation in hatcheries of Nile tilapia.