We analyse the expression of key growth genes namely; IGF-1, IGFBP-2, PRL and SL in hepatic and intestinal tissues amongst determined ‘slow’ and ‘fast’ growing fish fed a control diet and a magnesium supplemented diet (1% dry weight). Meagre were bred and reared onsite at EPPO in southern Portugal, where the trial was conducted in June of 2018 for a duration of 12 weeks. Juvenile meagre (body weight, 6.12±0.6 g; length, 8.03±0.33 cm) were kept in rectangular (1200 x 700 x 400mm) tanks at an initial stocking density of 12.2g/L. mRNA from the tissue was extracted, pooled and analysed for key growth genes after primers were designed in NCBI’s primer BLAST and analysed for binding efficiencies and secondary structures in vector NTI. The expression of key growth genes was analysed in hepatic and intestinal samples using RT-qPCR. It was found that i) IGF-1, PRL and SL are good bioindicators in identifying growth potential between slow and fast-growing fish ii) 1% dw magnesium supplementation is deleterious to somatic growth, iii) this negative effect is reflected in the genetic expression and ratios in hepatic and intestinal tissues, furthermore these are again differentially expressed in slow and fast-growing fish.
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