METABOLIC COMPARISON OF HATCHERY AND WILD SALMONIDS USING OTOLITH MICROSTRUCTURE AND ENZYME ACTIVITY

Hatchery culture of salmonids has become a standard in aquaculture and wild population restoration and enhancement. Because of frequent interactions between wild and hatchery-reared salmonids, domestication selection is potentially a serious problem and the physiological and selective mechanisms underlying domesticated behavior deserve close attention. We hypothesize that domesticated behavior in salmonids is caused by selection for elevated metabolic rates in the hatchery environment. Fish with an innate tendency for a higher metabolic rate (MR) may be favored in hatcheries because they develop faster, start exogenous feeding earlier, and are more aggressive competitors for food. A prerequisite for selection of high metabolic rate is that natural variation for relatively high or low metabolic rate exists and that this tendency is heritable. Although MR in fish varies greatly with temperature, body weight, life stage, and even time-of-day, there is inter-individual, probably persistent, variation in MR under identical environmental conditions (Metcalfe et al., 1995; Cutts et al., 1999). Egg development of individuals with a high MR has been shown to be accelerated. (Metcalfe et al., 1995; Cutts et al., 1999) and individuals with a higher MR are more aggressive and dominate over low MR individuals (Metcalfe et al., 1995; Yamamoto et al., 1998; Cutts et al., 1999). Growth rate of the otolith in larval fish is a function of basal MR rather than 40 somatic growth rate (Wright, 1991). In salmon from different populations raised under identical conditions, otolith size variation should reflect differences in MR at a given life stage. Similarly, although there is extensive variation in metabolic enzyme activity, often resulting from environmental effects or body-size scaling, the potential exists for heritable variation in enzyme functio