Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Renewable Natural Resources

First Advisor

William E. Kelso


A study of the biology, movements, behavior, and physiology of largemouth bass (Micropterus salmoides) from a low-salinity marsh in Lafourche Parish, Louisiana was conducted from March 1985 to December 1987. Comparative data were also collected for freshwater largemouth bass from Ben Hur Lake and False River, Louisiana. Marsh largemouth bass were small compared to freshwater bass of similar age, although growth rates of older marsh bass equaled or exceeded those of freshwater fish. Marsh bass relative weight indicated excellent condition during all seasons, while freshwater bass exhibited reduced condition in early spring and fall. Characteristic body morphology and growth of marsh bass suggest an adaptation to low-salinity environments. Salinity did not influence daily movements of ultrasonically-tagged largemouth bass, although salinity increases in late summer may have induced large-scale seasonal movements. Though tagged fish could not be located after salinities reached 8 parts per thousand (ppt), largemouth bass smaller than tagged individuals were collected in the study area. The presence of large predators combined with potential stressful physicochemical conditions may influence movements of largemouth bass in low-salinity environments. Salinity preferences of adult and young-of-the-year (YOY) largemouth bass indicated YOY marsh and freshwater bass preferred 0 ppt. Although adult marsh and freshwater bass preferred 3 ppt, mean number of observations at 0 ppt was significantly greater for freshwater bass, while mean number of observations at 3 ppt was significantly greater for marsh bass. Differences in salinity selection by adult largemouth bass between collection sites may be the result of long-term exposure to salinity. Experiments in which marsh and freshwater largemouth bass were exposed to 0, 4, 8, and 12 ppt salinity indicated no significant differences in plasma osmolalities, electrolyte concentrations, or gill ATPase activities between marsh and freshwater fish exposed to 0, 4, or 12 ppt. Exposure to 12 ppt resulted in osmotic stress in largemouth bass from both collection sites. At 8 ppt, marsh bass had significantly higher plasma chemistry values and lower gill ATPase activities than freshwater fish. Marsh bass appear to have adapted to environments of variable salinity by reducing energetic expenditures related to osmoregulation.