Routes of heat transfer in two teleosts,Ictalurus punctatus andLepomis macrochirus

Synopsis The proportion of heat transferred via the gills (Pg) was estimated for two morphologically divergent freshwater teleosts,Ictalurus punctatus (channel catfish) andLepomis macrochirus (bluegill). Methodology involved monitoring a fish's core temperature while its gills and skin surface were perfused with water of different temperatures. In both species, between 20 and 40 percent of heat was transferred via the gills. Pg depended on direction of the gill-skin temperature differential, suggesting that both species altered distribution of blood flow in response to polarity of the temperature differential. Pg of channel catfish was correlated positively with body mass; whereas, Pg and mass were uncorrelated in bluegill.