Growth, feeding and metabolism in juvenile Atlantic salmon Salmo salar L. Growth, feeding and metabolism were studied during the juvenile growth phase of Atlantic salmon. Comparisons were made between the faster and slower growing members of sibling populations which formed the upper and lower modes of a bimodal growth distribution. Several new techniques were developed in order to investigate these parameters in small fish. Specific growth rates of marked individuals within the bimodal distribution followed the same pattern of development as the whole population, and appeared to be more closely related to changes in daylength than ambient water temperature. Morphometric assessment of the growth of the swimming musculature showed that both processes of cell enlargement (hypertrophy) and cellular proliferation (hyperplasia) were important. The relative importance of the two processes was dependent on developmental stage and season, although hyperplasia appeared to be more a characteristic of rapid growth than hypertrophy. Histochemical studies demonstrated the presence of "red", "white", and between them a diffuse band of "pink" muscle which appeared to become less evident during the freshwater growth period. Modal differences in food intake were found between October and March, with the upper mode fish feeding optimally whilst the lower mode fish fed at only maintenance levels. Although no differences were found in food turnover rate, upper mode fish demonstrated an elevated temperature specific food intake and gross conversion efficiency. Photoperiod was an important influence on feeding, affecting both the daily feeding pattern, which was suppressed in darkness; and evacuation rate, which was more rapid for fish experiencing an increasing rather than decreasing photoperiod. Upper mode fish and smolts had higher resting rates of oxygen consumption than lower mode fish at two of the experimental temperatures used. Smolts had larger gills than either modal group, although no differences were found between fish in the upper and lower modes. However, upper mode fish had larger hearts than those measured in the lower mode. The higher levels of metabolism usually associated with smolting appeared to be a normal characteristic of the upper growth mode. The parameters studied are discussed in relation to the energy budget, and it is concluded that the two growth modes comprise two distinct "physiological populations" within the sibling group. Photoperiod is considered to be a primary influence on growth, and it is suggested that differential responses to seasonal and daily changes in photoperiod by individuals may account for both the development of bimodality, and provide the means (through an increased daily and seasonal feeding opportunity) by which higher growth rates are sustained by the upper mode fish.

Digestible carbohydrate is commonly encountered by chinook salmon {Oncorhynchus tshawytscha) in practical culture diets, although little is known regarding its utilization. This study was undertaken to examine (1) the effects of a high carbohydrate diet and (2) glucose tolerance in chinook salmon of selected British Columbia strains. Yearling chinook salmon of three strains were fed to satiation either a high or a low carbohydrate diet for 63 days. The diets were isonitrogenous, and contained respectively 30 % gelatinized wheat starch or an equicaloric amount of herring oil. There was an overall reduction in growth of chinook fed the high-carbohydrate diet over the 63-day feeding period. Although specific growth rates declined initially in the high carbohydrate-fed groups, they were comparable to those of control groups in the final third of the trial, indicating an adaptation response. Chinook fed the high carbohydrate diet had increased carcass protein and ash, and decreased carcass fat levels relative to controls. Feed intake was generally lower in these groups, and differences in feeding response were observed between diets and strains. Although feed and energy efficiencies were reduced in chinook fed the high carbohydrate diet, protein utilization was comparable on the two diets, indicating a protein-sparing effect of the carbohydrate. Consumption of the high carbohydrate diet led to significant elevations in hepatosomatic indices (HSI) and liver glycogen (LG) concentrations. In Quesnel chinook, LG levels exceeding 10 % did not appear to have any detrimental effects on feeding, growth or health. LG concentrations and HSI fell to basal levels in all groups 21 days after feed withdrawal. Some strain differences were evident. For example, Big Qualicum chinook fed the high carbohydrate diet exhibited the lowest liver glycogen accumulation, highest rate of carcass fat deposition, and best energy efficiency ratios relative to control groups, suggesting a difference in carbohydrate metabolism in this strain. On the other hand, Quesnel chinook exhibited the highest relative growth on the high carbohydrate diet. Mortality, although unaffected by diet in the Quesnel and Robertson Creek chinook, appeared to be higher in high carbohydrate-fed Big Qualicum chinook. In the second part of the study, chinook salmon subjected to an oral glucose tolerance test displayed pronounced and persistent hyperglycaemia, indicative of poor glucose tolerance. Strain differences were evident in the magnitude of response. Acclimation to a high carbohydrate diet prior to testing resulted in a significantly reduced elevation of blood glucose, indicating an adaptation response. While plasma glucose concentrations approached 500 mg/dl in some trials, plasma insulin concentrations exhibited a two-fold rise, with indistinct peaks. Plasma glucose and plasma insulin concentrations were poorly correlated, indicating that glucose is a poor insulin secretagogue in chinook salmon. / Land and Food Systems, Faculty of / Graduate