To establish an effective feeding regime for the aquaculture of genetically improved farmed Nile Tilapia Oreochromis niloticus (GIFT), this experiment investigated the effects of feeding frequency and daily ration on the growth of GIFT fry (initial weight, ca. 0.85 g). A factorial experiment design of two feeding frequencies (2 and 3 meals/d) and five feeding rates (2, 4, 6, 8, and 10% body weight per day [BW/d]) was carried out over 70 d with three replicates for each treatment. At the end of the experiment, fish from each treatment were sampled for the growth metrics of final body weight (Wt), weight gain rate (WGR), survival rate (SR), specific growth rate (SGR), and feed conversion ratio (FCR), as well as body composition and plasma metabolite measurements and histopathological analysis. The feeding frequency had a significant (P < 0.05) effect only on the Wt of fish. Feeding rates had highly significant effects on all the growth metrics (P < 0.01) except SR. The largest WGR and SGR were both observed in the fish receiving 6% BW/d at both feeding frequencies. The largest Wt was observed in the fish fed two meals daily at a 6% feeding rate. The relatively lower hepatosomatic index, liver contents, and body lipid also indicated better performance in fish that received 6% BW/d. In conclusion, these results suggest that a feeding rate of 6% BW/d and a feeding frequency of 2 meals/d is the most favorable protocol for the growth and physiological balance of GIFT during the fry phase.

Copper (Cu) is an essential nutrition trace element for Tilapia. However, the molecular mechanisms for the effects of Cu on Tilapia remain unknown. To explore the mechanism, 2,160 hybrid tilapia (Oreochromis niloticus × Oreochromis aureus) fries were used and evenly assigned to six groups and fed with different concentrations of Cu. After 60-day culture, physiological characters and biochemical parameters were measured. Spleen somatic index (SSI) was analysed, and distribution of trace elements was investigated. qRT-PCR was used to analyse the levels of immune genes. The result showed that 17 mg kg −1 of dietary Cu improved the growth rate, survival rate (SR), weight gain rate, condition factor and feed conversion ratio of hybrid tilapia (p < .05). Meanwhile, the dietary Cu increased the activity of superoxide dismutase and reduced the activity of glutathione (GSH), alanine aminotransferase, aspartate aminotransferase and lysozyme (p < .05). Sixteen mg kg −1 of dietary Cu did not affect SSI. Furthermore, dietary Cu affects the levels of immune genes, interleukin-1, tumour necrosis factor, MHC class IIB, pre-B-cell leukaemia transcription factor 1 and P450. Therefore, a certain concentration of Cu can improve tilapia performance by affecting its antioxidant and immune activity.

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