Can larval growth be manipulated by artificial light regimes in Nile tilapia (Oreochromis niloticus)

Photoperiod and light intensity have been shown to play important roles in the growth of larval fish. In terms of the effect of light conditions on the larval growth of Nile tilapia, previous studies are confined to examining the effect of only photoperiod rather than of their combined effects. The face-centered composite experimental design and response surface methodology were utilized to investigate the combined influences of photoperiod and light intensity on the feed conversion and larval growth of Nile tilapia in this study. Based on the results of pilot experiments, photoperiod ranged from 8 h to 24 h, light intensity from 100 lx to 2000 lx (1.26–25.20 μmol m−2 s−1). Results showed that under indoor recirculating rearing system varying growth rhythms occurred with different light conditions; interaction between the two factors was detected, and the light intensity was more important in impacting on growth than photoperiod in the larval stage, implying that light intensity and photoperiod ought to be examined in concert rather than separately. If light intensities are held invariable, the photoperiod studies would lead to the choice of >18 h photoperiod for the best larval growth. Response surface of the larval growth was roughly consistent with that of feed conversion, indicating that the larval growth was realized through feed conversion. Relationship of the larval growth and feed conversion to artificial light conditions could be reliably quantified in a second-order form, through optimization of which optimal two-factor combination, 14–16 h/1650–1900 lx (20.79–23.94 μmol m−2 s−1), was derived with the reliability as high as ca. 98%. There is therefore the potential for maximizing larval growth in hatcheries via manipulation of artificial light regimes. According to our findings, continuous lighting should not be recommended for optimal growth in larviculture. These findings underscore the important role of light conditions during the larval stage of Nile tilapia and should be taken into consideration for the optimization of rearing protocols in Nile tilapia hatcheries.