Heat transfer characteristics of isolated-perfused gills of rainbow trout

1.	Heat transfer was evaluated in isolated-perfused second gill arches and in isolated-perfused heads of rainbow trout.
2.	At a perfusion flow of 0.5 ml min–1 the second gill arch exchanges 0.774±0.024 ([`(X)]bar X±SE,n=6) cal min–1°C–1. This value can be increased by 11% with the infusion of 10–5 M epinephrine.
3.	With perfusion flows of 16 and 20 ml min–1, isolated-perfused heads had a transfer maximum (hAmax) of 21.27±0.57 (21) and 24.79±0.77 (21) cal min–1 °C–1 and a ventilatory flow ([(V)dot]dot Vg) resulting in 0.5hAmax transfer ([(V)dot]dot V0.5 max) of 144±17 (21) and 183±23 (21) ml min–1 respectively.
4.	The values of[(V)dot]dot V0.5 max were unaffected by the administration of 10–5 M epinephrine, 10–8 M or 10–7 M acetylcholine.hAmax was increased only in the presence of 10–5 M epinephrine.
5.	Increasing perfusion flow increasedhAmax without affecting[(V)dot]dot V0.5 max. At a given perfusion flow there were no changes in heat transfer when heart rate and stroke volume were varied.
6.	Analysis of a simple model for whole body heat exchange indicated that the gills may account for as much as 60% of the total heat exchanged by the animal.