FATIGUE AND EXERCISE TESTS WITH FISH

The terminology and classification of swimming speeds are summarized. The physiological basis for the classification of swimming speeds is briefly explained with regard to burst, prolonged, cruising speed, and the velocity which is critical to fish. The protocols of fixed (fatigue) velocity tests and increased (incremental) velocity tests are reviewed. The experiments carried out by different authors are compared with respect to their methodological approaches, the main focus being on the different time intervals and velocity increments employed. From the comparison, it appears that time intervals between 2 and 75 min have been employed. Yet, it is shown that there is agreement that time intervals of longer than 15-20 min are not necessary if the critical velocity alone is needed. The dependency of the critical swimming speed (CSS) on factors such as race acid population, size, season and temperature, sex, pollutants, light, food, training, and ambient gas content is outlined. The comparison shows that only the influence of pollutants and training on the CSS have been investigated in more detail, making further comparative studies on the dependence of the critical velocity on these factors necessary. Evaluation: since the CSS of fish depends on all these factors, it would appear to be a very sensitive measure for environmental or physiological factors. However, it is difficult to compare even intraspecific studies because of the individual variability and the dependence of swimming performance on the stock, population, gender and precondition level, making the calibration of the tests very complicated. It is shown that little is known about the mechanistic influence of internal or external factors on the CSS. Therefore, the CSS is of less interest for the physiologist than for the ecologist. Tests on the critical velocity have been successfully employed as an alternative to LD,, tests, although, once again, it is difficult to standardize the tests, and environmental factors, such as pollutants, may themselves influence the swimming performance since the metabolism can, in turn, in some cases depend upon the level of swimming performance itself.