Distinctive Aspects of the Ecology of Stream Fishes: A Review

Abstract

The essential feature of a stream is the continuous flow of water, and the various schemes of classification of streams and the associated fish fauna are largely based on factors which determine the average velocity. These schemes have been better developed in Europe than elsewhere, probably due to the relative uniformity of the climate. The characteristic features of fish inhabiting the more rapid streams can be related to the constraints imposed by this environment, and particularly by the need for the population to maintain its position against the continuous tendency of the stream to transport it downstream. Physiological factors associated with the normally high oxygen level and the need for continuous activity include a high routine metabolic rate, a high oxygen threshold for full activity, and, possibly, a high lower lethal limit for dissolved oxygen. Adult fish maintain their position either by continuous swimming in midwater, and these usually have a streamlined shape which is circular or laterally compressed in cross-section, or by avoiding the current and living closely attached to or in the substrate and these are usually dorso-ventrally depressed. The eggs are usually protected from the current by burying them in the substrate, sometimes in a well-developed nest. The general absence of vegetation in rapid streams results in the fish generally feeding principally on the available animal food, usually small invertebrates taken either in the drift or off the bottom. The solitary territorial behaviour which characterizes most stream-living fish probably leads to more even distribution and more efficient utilization of the food supply.