Somatic growth effects of intramuscular injection of growth hormone in androgen-treated juvenile Nile tilapia, Oreochromis niloticus (Perciformes: Cichlidae)

Abstract: Little is known about the effects of the interaction of growth hormone (GH) with 17 a-methyltestos-terone (17-MT) during fish growth. We evaluated this in the present study to assess the effect on fish growth. Fish in two batches of juvenile tilapia (Oreochromis niloticus) (approximately 5.0cm in length) were randomly assigned in triplicate to three treatments and a control group, distributed among 12 fiberglass tanks of 1 000L capacity (50 fish per tank) in an experiment covering a period of six weeks. The experimental groups were: a) fish treated with 17-MT and GH in mineral oil (RGH); b) fish treated with 17-MT and mineral oil without the addition of GH (R); c) fish treated with GH in mineral oil but not 17-MT (NGH); and d) fish of the control group, which were treated with mineral oil but not 17-MT or GH (N). The GH was injected into the fish at a rate of 0.625mg/g body weight. Morphometric data were recorded at the beginning of the experiment (T0) and at 15, 30 and 45 days (T15, T30 and T45), and various indicators of growth were assessed: condition factor (K); sur-vival percentage (S), feed conversion rate (FCR), percentage weight gain (WG) and (v) daily weight gain. The optimum dietary level was calculated assuming 5 % food conversion to total weight in each group. During the experiment, the fish were provided with a commercial food containing 45 % protein. The data showed that GH injection resulted in a greater weight gain in fish treated with 17-MT (the RGH treatment group), being particu-larly significant increase in weight during T15 and T30 (p<0.05). High values of K were found in the R and RG