Growth and protein turnover in fish
The aims of this thesis were to investigate the effects of the main abiotic and biotic factors on growth and protein turnover in fish. The first experiments were concerned with the effects of seasonal acclimatisation and temperature acclimatisation on tissue-somatic indices, nucleic acid concentrations/ratios and protein synthesis rates in cod. It was concluded that low water temperature resulted in an increase in tissue RNA concentration and reduced RNA (translational) activities. At the same time, protein synthesis rates were similar between cold and warm acclimated fish. Increased tissue RNA concentration at low water temperatures therefore appeared to be a thermal compensatory mechanism on protein synthesis rates in cod. The next experiment investigated the effects of ovine growth hormone administration on protein turnover and RNA concentration/activity in rainbow trout. Growth hormone administration generally stimulated protein synthesis rates resulting in larger fish; little effects on rates of protein degradation were observed. Stimulated protein synthesis rates were the result of both increased RNA/protein ratio and/or RNA activity. The final experiment investigated the effects of long-term nutritional regime and short-term alterations in nutrition on indices of growth rate in cod, with the aim of identifying the most sensitive indicator(s) of growth rate (nutritional status). Of all the indices examined, liver-somatic index, stomach and intestine nucleic acid concentrations/ratios and ventricle stomach and intestine cytochrome c oxidase activities were generally the best correlates of long-term growth rate as well as being sensitive to alterations in nutritional level. Whilst these data gave credence to the use of various correlates of growth rate under constant laboratory conditions, the use of these measurements as correlates of growth rate of wild fish may be limited under seasonally fluctuating environmental conditions.