Mechanisms of Heat Transfer and Time-Dependent Modeling of Body Temperatures in the Largemouth Bass (Micropterus salmoides)

Abstract

A time-dependent model describing mechanisms of heat transfer in fish was developed and tested. The model predicted thermal time constants of fish (100-1,600 g) and transient changes in body temperatures of fish experiencing step changes in ambient temperature (heating or cooling). Model sensitivity analysis indicated that body diameter, insulation thickness, and tissue thermal conductivity were controlling variables in the transfer of heat between a fish and water. Fish metabolic rate and water velocity across fish surfaces did not appreciably affect heat transfer rates. Results from experimental heating and cooling studies performed on Micropterus salmoides indicated that body wall thicknesses for three anatomical compartments (midgut, brain, and heart) were linear functions of body mass. Midgut and brain thermal time constants were dependent on body mass. Heart thermal time constants were independent of body mass, indicating that the temperature of the heart may be a factor limiting the thermal exploitive behavior of different-size fish. The midgut region exchanged heat at the slowest rate and the heart region exchanged heat at the fastest rate. The cranial region exchanged heat at rates intermediate to those of the midgut and heart. We found statistically significant differences between deep body thermal time constants of live and dead M. salmoides, indicating differential mechanisms of heat exchange for living and nonliving fish.