Ontogenetic and Non-Thermal Seasonal Effects on Thermal Preferenda of Fish

Abstract

Ontogenetic and non-thermal seasonal effects on thermal preferenda of fishes were sought both by a general review of the literature and by examining those papers in which such effects were evident. The growing list of other non-thermal factors that have been shown to influence thermal preferenda made this search difficult, since these factors could conceivably obscure subtle ontogenetic and non-thermal seasonal effects. Those few studies, however, in which ontogenetic effects were intentionally studied support the hypothesis that young fishes select higher temperatures than do older conspecifics; this is consistent with distributions in nature, in which younger fishes are often found in shallower, warmer waters than the adults. Pronounced non-thermal seasonal effects have been demonstrated in some species, while in others litde or no such influence was evident. In spite of conflicting evidence which precludes generalities, the age of a fish and the season of the year are among the factors to be considered or specified in describing the preferred-temperature relations of species.