The comparative physiology of fathead minnows and rainbow trout: Insights into the tolerance of the two species to toxicants

Abstract

<p>In this thesis the physiological systems of two unrelated freshwater fish with different tolerances to many toxicants were compared. Comparisons were made between fathead minnow (FHM) and rainbow trout (RBT) that were approximately 1.5 g. Differences between the two species were found in gill function and morphology, detoxification, and cellular resistance. The greater sensitivity of FHM than RBT to H+ ions was related to the fact that FHM appeared to regulate ions with less precision than RBT. There were significant linear relationships between whole body Na+ (r2 0.24) and Cl- (r2 0.33) and temperature as well as with Na+ uptake (r2 0.70) and temperature in FHM after up to 2 months acclimation. In contrast there were no significant relationships between these parameters and temperature in acclimated RBT. In addition, FHM did not up-regulate Na+ uptake even after they had lost up to 31% of whole body Na+ whereas there were 2-fold increases in RBT after whole body Na+ losses of 22%. The greater tolerance of FHM than RBT to ammonia and organic toxicants was partially attributed to lower gill uptake of these compounds. The activity rates of the ammonia detoxifying enzyme, glutamine synthetase were 1.7-fold higher in FHM than RBT. Fathead minnows also had 1.7-fold higher activity rates of the phase II biotransformation enzyme, glutathione-s-transferase, than RBT. Fathead minnows also tolerated higher tissue concentrations of ammonia, and monochlorobenzene than RBT. Finally, the sprint test was a useful measure of swim performance in both species. The rank order of individual sprint performance was reproducible in FHM (Spearman's rank coefficient (rs 0.95)) and RBT (r s 0.92), and sprint performance was impaired in FHM and RBT with acute exposure to ammonia. However, in FHM sprint performance declined when sprints were repeated at 24 h intervals whereas it was unaffected by this treatment in RBT. (Abstract shortened by UMI.)</p>