Combined effects of temperature, body size and food density on swimming behaviour and growth of juvenile brook trout (Salvelinus fontinalis)

Liu, Lidong (1998) Combined effects of temperature, body size and food density on swimming behaviour and growth of juvenile brook trout (Salvelinus fontinalis). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This study is an attempt to quantify experimentally the body size allometry and thermal dependence of foraging rate (swimming velocity) in juvenile brook trout (Salvelinus fontinalis) under different food densities. The results of behavioural experiments on swimming velocity were used in conjunction with additional experimental data on maximum feeding rate and growth rate to carry out a theoretical analysis of the potential effects of changes in body size, temperature, and food density on growth, habitat use, and adult size. -- This study differs from previous studies of salmonid feeding in that the foraging movements of individual fish were tracked in real time through a computerized monitoring and control system that provided an accurate quantitative measure of the distance swum vs. time. The monitoring and control system automatically dispensed a food item each time an experimental fish had swum a prescribed distance. The distance swum per food item consumed, a measure of food density, could thus be held constant for any combination of temperature and body mass treatments, allowing for the investigation of the effects of temperature, body mass and food density on feeding behaviour under conditions close to those encountered in a natural foraging environment. -- The results of the foraging activity experiments show that the total distance swum, the proportion of time spent actively foraging, and swimming speed are all positively affected by both body mass and temperature, but not by food delivery schedule. The data are clearly not consistent with an optimal foraging model in which foraging velocity is predicted to decrease with increasing body mass and increase with increasing food density. -- The body mass allometric scaling factors for total distance swum (0.33-0.56), foraging time (0.21 -0.46), and swimming speed (0.10-0.12) at 5, 12, and 18 ﾟC are all markedly lower than the scalings for maximum feeding rate and both standard and active metabolic rates of fish. The allometric scalings for instantaneous and daily swimming costs, however, are close to the scalings for metabolic rates at all three temperatures, suggesting that swimming speeds are regulated by the instantaneous costs of swimming rather than its energy benefits. Because the rate of energy intake is directly proportional to the distance swum, the scaling for energy intake is expected to be well below that for energy requirements. -- In contrast to the situation for body mass, the values of the Van't Hoff thermal parameter for distance swum of experimental fish are close to those for sustained swimming speeds and the frequency of muscle contraction and tail beat of most fish, and also comparable to those for the standard and active metabolic rates of fish. This suggests that distance swum may respond to temperature changes in a way that parallels metabolic rate. If energy intake is a linear function of distance swum, then equivalent temperature scalings of distance swum and metabolic rate would mean that food intake should parallel temperature related changes in metabolic requirements. -- The growth rate data is consistent with previous studies and shows that there is a positive relationship between ration and the temperature for maximum growth at any body mass. Daily growth rate increases with increasing temperature at high ration level but decreases at low ration level. As a result, the temperature for maximum growth decreases as food density is decreased. -- The analyses of growth rate in actively foraging fish indicated that growth rate should increase with both body mass and temperature at high food densities, and decrease with both body mass and temperature at low food densities. At intermediate densities the situation was more complex as the effect of body mass and temperature on growth rate depended on food density, body size, and temperature. In the low food density simulation, Wmax, the body mass at which absolute growth rate is zero, is sensitive to both food density and temperature. Wmax is predicted to increase with increasing food density but decrease with increasing water temperature. -- The analyses of growth in actively foraging fish suggested that the temperature at which growth rate is maximized decreases with decreasing food density and increasing body mass. These results are consistent with previous studies of the effects of temperature on habitat use in fishes. It was not possible to draw any conclusions regarding the effect of temperature on adult size from the results presented in the thesis.

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