Experimental administration of recombinant bovine growth hormone to juvenile rainbow trout (Salmo gairdneri) by injection or by immersion

Abstract The ability of recombinant bovine growth hormone 21K (rbGH-21K) to accelerate the growth of juvenile rainbow trout (Salmo gairdneri) was investigated, and the potential of bath immersion as a method of administration of growth hormone was assessed. Injection of 10 μg/g rbGH-21K every 2 weeks for 8 weeks resulted in a highly significant increase in the rate of growth in both weight and length as well as an increase in condition factor. Administration of rbGH-21K by immersion at a dosage of 100 mg/l for 4 h every 5 days resulted in a significant increase in specific growth rate relative to similarly treated controls during the 8-week treatment period, although the effect was minimal when compared to the injected group. Comparison of growth in immersed versus non-immersed controls indicated that the immersion protocol itself inhibited growth. Modifications to the immersion protocol which may improve its effectiveness are discussed.