Term of Award

Spring 1991

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Committee Chair

J. B. Claiborne

Committee Member 1

james H. Oliver, Jr.

Committee Member 2

Timothy Spira

Abstract

In this study, two species of fishes were exposed to varying salinities of ambient seawater in order to determine the effects of such salinity changes on acid-base relevant ions. The long-homed sculpin (Myoxocephalus octodecimspinosus) is considered to be a stenohaline fish, not often encountering or withstanding changes in environmental salinity. The oyster toadfish (Opsanus tau), however, is an inhabitant of estuaries where environmental salinity varies on a regular basis and is, therefore, considered to be euryhaline.

The sculpin were able to withstand ambient water dilutions for 24 - 48 hours (varying depending on the salinity) before they expired. Toadfish, in contrast, were able to withstand all salinity changes to which they were exposed for up to two weeks at which time the experiment was terminated and the fish were released.

The most striking change that occurred during the sculpin experiments was an observed loss of bicarbonate ions (an absolute acid-base relevant ion, Heisler, 1984) to the ambient water as well as a loss of ammonium ions. It appears from the results obtained that the sculpin were becoming very acidic when exposed to low environmental salinities. Toadfish, on the other hand, were able to alleviate their bicarbonate loss within a few days and were not apparently affected by the change in environmental salinity.

In addition, sculpin were exposed to low salinities with added calcium and added bicarbonate to determine whether either condition could assist them with their adjustments for survival. In both experiments, the animals still expired in the dilute water. Transepithelial potentials (T.e.p.'s) measured in the sculpin showed that sodium was possibly moving along an electrochemical gradient while chloride would have to be actively transported out of the animal. T.e.p.'s measured in toadfish are slightly negative (Evans, 1979), so both sodium and chloride must be actively transported. It is suggested here that the euryhaline toadfish is capable of changing the active transport of ions affecting ion/acidbase balance that occurs at the gills whereas the stenohaline sculpin is limited in its ability to do so.

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