Factors governing prolonged swimming performance of juvenile rainbow trout (Oncorhynchus mykiss)

Abstract

<p>This study investigated the factors governing prolonged swimming performance in juvenile hatchery-reared rainbow trout. The primary exercise test used was a fixed velocity sprint test in which fish were rapidly accelerated to a speed of 6-7 body lengths s-1 . Time-to-fatigue was recorded as the measure of endurance. The ultimate goal of this research was to develop a model describing the limitations of sprint performance in juvenile trout under conditions of imposed velocity. This was accomplished through the completion of five studies. The specific objectives of the first study were to examine the effects of varying the rate of acceleration and the influence of experience (i.e. training) on sprint endurance. The second study examined the relationship between endurance and fuel depletion in white muscle [i.e. glycogen, phosphocreatine (PCr) and ATP], to determine whether a specific metabolic change within the muscle evoked fatigue. The dependence of endurance on muscle glycogen levels was also assessed by manipulating glycogen in two ways, through elevated ration and through sprint training. The third study examined the effect of creatine supplementation on muscle total creatine levels and endurance to determine the importance of creatine and PCr stores. The fourth study exploited individual variability in sprint performance to correlate other physiological performance measures [e.g. growth, critical velocity (Ucrit ) and response to induced stress] with endurance. The fifth and final study examined the effect of oxygen supply on swim performance. Together, these five studies have produced the following results: slowing the rate of acceleration and periodic sprint training both increase endurance; chronic stress reduces the ability to train; the reduction of ATP appears to evoke fatigue in both Ucrit and sprint tests; glycogen levels do not determine endurance; creatine loading enhances endurance via a mechanism independent of muscle free creatine and PCr levels; fish with high sprint performance have a higher Ucrit , but most other physiological performance measures do not correlate with swim performance; Ucrit performance is oxygen diffusion limited in high performers, but is more convectively limited in low performers; convection limitations are more important following a rapid acceleration in both groups; and neither sprint nor Ucrit performance is influenced by blood oxygen carrying capacity. This study has led to the conclusion that endurance is determined by cardiovascular response, specifically the ability to perfuse white muscle, rather than by the amount of fuel in the muscle to power swimming.</p>