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

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