Thesis Title

Effects of the Exotic Cladoceran Daphnia Lumholtzi (Sars) on the Growth Rate and Prey Selection of Bluegill Sunfish (Lepomis Macrochirus Rafinesque)

Date of Graduation

Spring 1998


Master of Science in Biology



Committee Chair

John Havel


Daphnia lumholtzi, a large cladoceran native to the Old World tropics, has recently invaded lakes in the southern U.S. this invasion has provided a unique opportunity to study its effects on native fish. Prior research has shown the presence of D. lumholtzi interferes with the feeding of larval bluegill, which may stunt their growth. However, D. lumholtzi may enhance growth in larger bluegill, since D. lumholtzi are most abundant during midsummer, a period when native large-bodied Daphnia are typically rare in the plankton. The purpose of the current study was to look at the impacts of community structure (D. lumholtzi invaded vs. native zooplankton) and food abundance on the survivorship and growth of three size classes of bluegill sunfish (15-25, 30-40, and 50-60 mm). Prey selectivity values also were determined for each of the zooplankton species from the exotic community type for each of the tree bluegill size classes. Results indicated that food level had strong effects on growth rates of all bluegill size classes. The exotic community type weakly depressed growth of small juveniles (15-25 mm) and enhanced growth of large juveniles (50-60 mm). Medium juveniles (30-40 mm) showed a neutral effect. Results from the prey selection experiment were consistent with the growth rate experiments. Selectivity values of the smallest size class of bluegills were negative for D. lumholtzi, whereas those of the largest size class were strongly positive. If the abundance of D. lumholtzi in the plankton is high during a critical growth period for small juvenile bluegills, growth and survivorship may be reduced and subsequent recruitment to older age classes may be limited. Once fish grow beyond mouth gape limitations for D. lumholtzi, this exotic may serve as an added food resource when there are no large-bodied cladocerans in the plankton. The results of this study suggest that the invasion of zooplankton communities by D. lumholtzi can affect growth of bluegill sunfish.

Subject Categories



© Earl Matt Eisenbacher