Survival Time of Trout in Relation to Occurrence

Abstract

The reactions of brook, rainbow, and brown trout fingerlings were tested under various experimental conditions: Straight survival, high temperature, low oxygen tensions, high pH, low pH and high concentrations of NaCl. As judged by length of survival under extreme conditions, the brook trout is the hardiest fish of the three. All three species showed equal susceptibility to high temperature. The brook and brown trout were about equal in survival value in solutions of very low pH and greatly exceeded the rainbow in this respect. Under all other conditions the brook trout exhibited the greatest resistance in terms of longest survival. Degrees of tolerance, not ordinarily believed possible, were found for these ''sensitive'' fish. The limits of variability of the natural hibitat of each species are well within the extremes of the toleration range of all. The distribution of trout is not a matter of toleration alone, but involves an actual choice of habitat. Each species takes up a position in the stream where the balance of biotic, as well as physical, conditions is compatable to its existence.