Date of Award

Spring 2020

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Biological, Environmental, and Earth Sciences

Committee Chair

Jake Schaefer

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Brian Kreiser

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Scott Clark


The Pascagoula River in southeastern Mississippi is the largest remaining un-impounded river system in the contiguous United States and have seen a change in fish assemblages over time. Examination of long-term fish assemblage data show that the mainstem Pascagoula River and its two major tributaries (mainstem Leaf and Chickasawhay Rivers) have been dominated by five abundant taxa that comprise 83% of individuals sampled, with Cyprinella venusta in the highest abundance. Beginning in about 2005-2006, a change in the mainstem Pascagoula River (but not mainstem Leaf and Chickasawhay rivers) was seen to an alternate assemblage where five different taxa dominate (89% of assemblage), with Hybognathus nuchalis now the most abundant species. Thus, a shift in fish assemblages seems to have occurred in one portion of the drainage but not the other. A potential driver for the switch in historic versus contemporary assemblage composition could have been changes in the abiotic environment, most specifically in dissolved oxygen (DO) within the Pascagoula River. Because of the differences in tolerances to the abiotic environment, H. nuchalis may be able to utilize a broader variety of habitats compared to C. venusta and be a notable factor in the reason there is a shift in relative abundances in assemblages. Hybognathus nuchalis can withstand pools and backwaters that are lower in DO and might do better in more extreme conditions, while C. venusta is unable to tolerate the harsher environments.