Influence of Extended Photoperiod on All Male Nile Tilapia (Oreochromis niloticus) Production, Differential Gene Expression and Growth Rate

The effects of an extended photoperiod (18 h light or 12 h light), using a combination of natural and artificial light sources, on the differential gene expression and growth rate of Nile tilapia Oreochromis niloticus L. were evaluated. Four groups of all males tilapia (n=10) with initial mean body weight of 102.25 g were reared in an aquaria with two replications for each treatment. The experiment was conducted during a period of 35 days, growth rate and water quality (dissolved oxygen, pH, nitrite, nitrate) were measured weekly, temperature and solar radiation were recorded daily. At the end of the experiment we used a zebrafish genome array to study differential expression over 14,900 transcripts and to test the hypotheses that an extended photoperiod stimulates growth rate and causes differential gene expression in tilapia. Fishes in the extended photoperiod group (Ep) were susceptible to show higher growth rate (GR) compared with the standard photoperiod group (Sp; P = 0.001). Food conversion efficiency in the Ep was superior than the Sp. Differential expression of genes related to transcriptional regulation for biological function was detected using zebrafish GeneChip(R) (Affymetrix) microarrays, this could explain how the fish alters their metabolism as response to this phenomena.