Effects of bovine growth hormone (Posilac®) on growth performance, body composition, and IGFBPs in two strains of channel catfish

The effects of recombinant bovine growth hormone (rbGH; Posilac(R)) on growth rate, feed efficiency, body composition, and insulin-like growth factor binding proteins (IGFBPs) were investigated in Norris and NWAC103 strains of channel catfish. Three hundred and twenty fish from each strain were assigned randomly to four treatments with four replicates each. The treatments were (1) Sham-injected control (needle puncture per 3 weeks); (2) Low (30 mug g(-1) BW per 3 weeks, Posilac(R)); (3) Medium (60 mug g(-1) BW per 3 weeks, Posilac(R)); and (4) High (120 mug g(-1) BW per 3 weeks, Posilac(R)). Fish were reared in 76-1 tanks supplied with 26.0 degreesC flow-through well water for 9 weeks. Fish were fed a 36% CP commercial diet twice each day to apparent satiation. Feed consumption increased (P < 0.05) 15% with rbGH treatment in the Norris strain while no significant increase in feed consumption was observed in rbGH-treated NWAC103 catfish. Compared to sham controls, all treatments (Low, Medium, and High) increased final weights (P < 0.05) (168 +/- 13.2 vs. 144 +/- 10.0 g) (average weight of the three treatments), but no overall improvement in feed conversion ratio (FCR) was observed in NWAC103 fish. In the Norris strain, the High treatment increased (P < 0.05) final weight (135 +/- 6.2 vs. 106 +/- 8.7 g) but no improvement in FCR was observed when compared to sham controls. rbGH treatments increased (P < 0.05) total length in both strains, but no difference in condition factor (CF), hepatosomatic index (HSI), or body composition was observed. On day 63, levels of a 45-kDa IGFBP (catfish-IGFBP-3) were similar between treated and untreated fish in both strains. Results of this study indicate the Low treatment was as effective in promoting growth as the High treatment in the NWAC103 strain. Results of the body composition analysis suggest that the increase in weight gain was not due to an increase in fat deposition. The observed increase in length suggests rbGH enhances linear growth in channel catfish. Similar levels of cf-IGFBP-3 between treated and untreated fish may reflect steady state levels of cf-IGFBP-3 in growing fish. Identifying other endogenous growth factor(s) responsible for the observed increase in growth rate will be crucial in our understanding of improving growth in cultured channel catfish. Published by Elsevier B.V.