EVALUATION OF A SUSTAINED-RELEASE POLYMER-ENCAPSULATED FORM OF RECOMBINANT PORCINE SOMATOTROPIN UPON LONG-TERM GROWTH-PERFORMANCE OF COHO SALMON, ONCORHYNCHUS-KISUTCH

The effect of sustained-release recombinant porcine somatotropin (RPST) treatment upon growth performance of coho salmon was examined over a 95-week period. Animals were implanted with one of 4 types of RPST-containing capsules, or were placebo-treated as controls. The encapsulated RPST exhibited different liberation kinetics, in that protein release was inversely proportional to the thickness of the polymer coating. Fish implanted with pellets with the highest release rates for RPST during a 14-week period maintained a weight advantage over the control group until week 77, while the advantage in terms of length was maintained for 95 weeks. Specific growth rates (SGR) for weight were significantly greater in fish treated with the capsules which exhibited the highest RPST release over the first 26 weeks of the study when compared to controls. However, between weeks 26 and 52, weight SGR was similar in all groups. At trial termination, significant differences in relative intestinal length, visceral and gonadosomatic indices were noted between the group implanted with capsules expressing most rapid RPST release and the placebo-implanted fish. Significant decreases in body lipid levels, relative to initial values, were observed in fish implanted with capsules expressing the two highest release rates.