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The effects of both long-term (35 d of daily feeding, feeding every second day, or starvation) and short-term (up to 15 d of refeeding following starvation) nutritional regimes on morphological (tissue-somatic indices) and biochemical measurements (RNA concentration, RNA/protein ratio, RNA/DNA ratio, and cytochrome c oxidase activity (CCO)) were investigated for a variety of Atlantic cod (Gadus morhua) tissues. Liver-somatic index was the morphological index most sensitive to both the long- and short-term nutritional regimes. The majority of the tissue RNA measurements demonstrated positive linear relationships with growth rate, although stomach, intestine, and white muscle were the most sensitive tissues for all the treatments. Most of the tissues examined also showed positive linear relationships with growth rate, although stomach, intestine, and white muscle were the most sensitive tissues for all the treatments. Most of the tissues examined also showed positive linear relationships between CCO specific activity and long-term growth rate. However, tissue CCO specific activity was relatively insensitive to the short-term alterations in nutritional regime.

Juvenile cod were acclimated to cold (5 °C) and warm (15 °C) water temperatures and fed sandeel at a similar ration size (3% body weight∙day−1) for at least 40 days. After this acclimation period, there were no significant differences in either weight-specific growth rate or weight-specific tissue protein synthesis rates (ventricle, gill, stomach, and intestine) between the cold- and warm-acclimated fish. However, every cold-acclimated tissue examined had a significantly higher RNA concentration (μg RNA∙g tissue−1) than the respective warm-acclimated tissue. Cold-acclimated ventricle and intestine had significantly reduced RNA activities (i.e., translational efficiency, g protein synthesized∙g RNA−1∙day−1) compared with the warm-acclimated tissues. In contrast, the mean RNA activities of cold-acclimated stomach and gill were not significantly different from those of the same tissues in the warm-acclimated fish. These alterations in RNA activity and RNA concentration with temperature acclimation probably represent a thermal compensatory mechanism for protein synthesis and growth in cod at 5 °C. Positive linear relationships were observed between tissue protein synthesis rates and tissue RNA concentrations (μg RNA∙g tissue−1). RNA/protein ratios (μg RNA∙mg protein−1) gave a positive (but statistically insignificant) trend with protein synthesis rates. In contrast, a negative trend (statistically insignificant) was observed between tissue protein synthesis rates and tissue RNA/DNA ratios (μg RNA∙μg DNA−1). The use of RNA measurements as biochemical correlates of growth rate in juvenile cod is discussed.

Ovine growth hormone (oGH) was administered to rainbow trout via an intraperitoneal cholesterol implant. After 21 days, plasma oGH levels were recorded as control group, <2 ng ml -I, i.e., not detectable, and oGH group, 19.2 t 2.8 ng ml-'. oGH-treated fish exhibited significantly increased whole-body growth rates, whole-body protein accretion rates, stimulated tissue protein synthesis, and tissue protein accretion rates. A dramatic decrease in white muscle protein concentration was also observed after oGH treatment. In some tissues (liver and stomach), elevated protein synthesis rates were the result of higher RNA/ protein ratios. However, in other tissues (gill and ventricle), increased RNA activity accounted for the differences in rates of protein synthesis. The growth promoting effects of oGH on both whole-body and tissue protein turnover were generally accompanied with no change in the efficiency of deposition of newly synthesized protein. For the same ration size, the oGH group showed higher retentions of ingested nitrogen. It is concluded that oGH significantly enhances whole-body growth rates as a result of the stimulatory effect on protein synthesis rates with little effect on protein degradation. o IW Academic PXS~. IWZ

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