Predicting Body-Core Temperature in Fish Subjected to Fluctuating Ambient Temperature

A simulation model, based on Newton's law of cooling, was developed to predict body-core temperature in fish subjected to fluctuating ambient temperature. Under the model, body temperature "decays" exponentially, with rate coefficient k, toward the equilibrium temperature that existed L time units earlier. The latency period L is presumably indicative of the time required for the initial transfer of heat between a fish's deep-body tissues and its external surfaces. The computerized model simulated body temperature at 10-s intervals for comparison with that actually measured in five Lepomis macrochirus, two Tilapia aurea, and three T. nilotica as ambient temperature cycled irregularly between 18 and 33 C. The mean absolute error between observed and simulated body temperatures (411-540 comparisons per fish) ranged from 0.04 C (145.9 g T. nilotica) to 0.24 C (89.6 g T. nilotica). The maximum absolute error per series ranged from 0.14 C (145.9 g T. nilotica) to 0.67 C (89.6 g T. nilotica). Over 90% of the 4,564 prediction errors for the 10 fish were less than ± 0.3 C (mean absolute error = 0.13 C). The parameters k and L were estimated for each fish from thermal step-change experiments that both preceded and followed the cyclic-temperature experiment. Precyclic estimates of k were greater (P < .01) than postcyclic estimates at both the genus and combined levels. Lepomis macrochirus warmed faster than they cooled (P < .05). Data combined for the three species indicated a linear relationship between In k and In weight, with slope -0.59. Latency times were not correlated (P > .10) with fish weight, nor did they differ (P > .05) between pre- and postcyclic trials. In L. macrochirus, warming latency time was longer than cooling latency time (P < .05).