DISSOLVED-OXYGEN AND FISH DISTRIBUTION IN A FLORIDA SPRING

This study examined the distribution and relative abundance of fishes along a dissolved oxygen gradient in Singing Springs, Florida. Over th e 1-year study, dissolved oxygen concentration in the spring exhibited a strong gradient ranging from an average of 0.20 mg l(-1) at the boi l to 1.81 mg l(-1) 110 meters downstream. Season al variation in disso lved oxygen was very low relative to the spatial variation along the s pring gradient. Fish community composition was evaluated monthly at th e boil of the spring, 45 m downstream just after the confluence of the spring and the main river, and 110 m downstream. The fish community i n the spring was characterized by species generally considered to be t olerant of low oxygen. Gambusia holbrooki was the most abundant specie s at all sites comprising an average of 88.1% of the fish captured at the boil, 63.2% of the fish captured at 45 m, and 74.8% of the fish ca ptured at 110 m downstream. The diversity of fishes (G. holbrooki, Het erandria formosa, Notropis harperi, Lucania goodei, and Poecilia latip inna) increased with distance from the boil. Although there were some seasonal differences in patterns of diversity and community structure, the inter-site differences were much more apparent throughout the stu dy. II is likely that the pattern of variation in dissolved oxygen int eracts with the respiratory abilities of the fishes to affect the dist ribution pattern and community composition along the gradient.