Impact of a controlled release formulation of recombinant bovine growth hormone upon growth and seawater adaptation in coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon

Experiments were undertaken to evaluate a sustained release recombinant bovine growth hormone (rbGH) formulation (Posilac(R)) in salmon. The investigation was divided into two parts. The first series of studies was used to establish optimal dosages and clearance rates for the exogenous protein in size-selected coho salmon, and to examine the effect of rbGH treatment upon smoltification. The second series of studies attempted to mimic the production setting, where chinook salmon were randomly selected from a stock of animals, and taken through smoltification to grow-out. In the first experiment, coho salmon were provided with a single injection of one of three doses (420, 1260, 4200 mu g/g body weight equivalent) of the rbGH preparation (n greater than or equal to 30/group), or were injected with a saline solution containing the high dose equivalent of rbGH. Controls were treated with BSA, given one of three (10, 30 or 100 mu l) placebo carrier preparations without rbGH, or left untreated. Animals receiving rbGH by sustained-release expressed highly significant (P < 0.01) growth acceleration over a 20-week period of observation, when compared with the five control treatments. There were no significant differences in growth between the five control treatments. At the termination of the trial, control animals had doubled their weight and were 25% longer than starting values. In contrast, salmon receiving rbGH via sustained release were 5-7.5 times their starting weight and exhibited a 60-100% increase in length. Coho salmon injected once with the saline solution of rbGH grew significantly (P < 0.05) larger than control groups over the first 16 weeks of observation. However, at trial termination, control and saline rbGH animals were not statistically different in weight and length. Following the growth trial. fish were subjected to a 24-h seawater challenge. Plasma samples collected prior to and following challenge. indicated that rbGH-treated fish were better able to adapt to the hypersaline environment, as indicated by their increased ability to regulate plasma sodium (P < 0.05). Plasma profiles for rbGH determined that the protein was released from the Posilac(R) preparation for greater than or equal to 20 weeks following injection. In the second experimental series, chinook salmon were provided with the high dose Posilac(R) formulation (equivalent to approximately 6600 mu g rbGH/g body weight), whereas controls received the placebo carrier alone (n = 856 for each group). The growth response was followed through transfer to sea water, and beyond for a period of 32 weeks. Significant differences (P < 0.01) between group weights and lengths were first observed following 12 weeks of observation, and maintained until trial end. Examination of size frequency distribution illustrated a significant (P < 0.05) broadening of the curves for rbGH-treated fish from week 8 onwards, indicating an overall increase in size variation. (C) 1997 Elsevier Science B.V.