VENTILATION FREQUENCY COMPENSATION RESPONSES OF 3 EURYTHERMAL ESTUARINE FISH EXPOSED TO MODERATE TEMPERATURE INCREASES

Ventilation frequency patterns of Trinectes maculatus, Morone americana and Leiostomus xanthurus were used to evaluate potential thermal stress after exposure to moderate temperature increases. Fish acclimated to 5.degree., 15.degree. and 25.degree. C were exposed to a 5.degree. C .DELTA.T; fish acclimated to 30.degree. C were exposed to a 2.5.degree. C .DELTA.T. Ventilation frequencies were measured at each acclimation temperature before the fishes were exposed over a 15-min period to the increased temperatures. Ventilation rates were then measured at the elevated temperatures for the next 24 h. Significant increases in rate frequency occurred after the temperature increases in T. maculatus and M. americana acclimated to 5.degree., 15.degree. and 25.degree. C and in L. xanthurus acclimated to 15.degree., 25.degree. and 30.degree. C. Rate frequencies generally increased as the temperature increased. Ventilation rates stabilized quickly at the higher temperatures and remained relatively constant throughout the remaining exposure period. Acclimated rate-temperature curves (R-T curves), acute R-T curves and Q10 temperature coefficients used to assess the significance of the changes in rate frequency and to compare the species in an ecologically meaningful way, showed that several adaptive types occurred among and between species. The Q10 of the acute R-T curves in most cases were found to approximate those values derived for the acclimated R-T curve. The temperature increases had a negligible effect, i.e., little or no thermal stress occurred.