Lake Weir is a mesotrophic lake locates in central Florida, approximately 30 miles south of Ocala in Marion county. The lake is 5685 surface acres and an average depth of 20 feet (McKinney et al., 1989). The lake has numerous private residences along its shoreline as well as several public beaches and boat ramps. Historically, the lake has been highly valued for its exceptional game fish population. Since 1984, however, fisheries biologists have received complaints of sporadic fish kills and declining catch. Annual population estimates have suggested a decline of largemouth bass (Micropterus salmoides) and complete disappearance of black crappy (Pomoxis nigromaculatus).

Anemic largemouth bass were first collected in June 1986 and submitted to the Department of Fisheries and Allied Aquaculture at Auburn University. A cause of the anemia was never determined but: the parasite load in affected fish was considered excessive. In June, 1986 fish with white gills were also submitted to the Florida Department of Environmental Regulation for toxicology studies. Findings were inconclusive. In February 1988 10 largemouth bass were collected for hematologic assessment at the University of Florida. Of these fish, only one was considered to have a normal packed cell volume, based on data available for rainbow trout (Salmo gairdneri) (Miller et al., 1983) and channel catfish (Ictalurus punctatus) (Brader et al., 1982).

As normal hematologic parameters for largemouth bass and black crappy were poorly defined a comparative study was initiated using fish from Lake Holly as a control group. Lake Holly is located approximately 30 miles east of Lake Weir in Lake county and has similar immunological characteristics. The most obvious difference between the two lakes is that Lake Holly is relatively pristine with no residential development and minimal agricultural development immediately adjacent to its shoreline. No fish kills have been reported from Lake Holly, and its populations of largemouth bass and black crappie are believed to be quite healthy.

During the 12 month study period 30 fish were collected from each lake at monthly intervals. Blood was collected into heparinized tubes and standard hematologic parameters were measured. During each sampling period 9 fish from each lake were sacrificed and tissues collected for pathology studies.

Data analysis has not been completed, however a preliminary assessment suggests that 10 to 20% of the largemouth bass collected from Lake Weir were anemic (PCV <20%), and that the incidence of anemia may vary seasonally. No anemic fish were collected during the winter months from Lake Weir, or from Lake Holly at any time.

Preliminary findings suggest that the anemia may be nonregenerative, microcytic and hypochromic. Confirmation of this assessment will rule out chronic parasitism as a cause of the condition. This conclusion is supported by necropsy findings. Possible environmental causes of the poor condition of largemouth bass in Lake Weir will be pursued.

Acknowledgment

Funding for this study was provided by the Florida Game and Fresh Water Fish Commission.

References

1.  Brader, J.D., Freeze, T.M., Goetz, R.C. 1982. Hematologic values of blue and channel catfish from two Kentucky Lakes. Trans Ky Acad Sci 43 (1-2) :4-9.

2.  McKinney, S.P., Kittrell, W.B. Jr., Owen, G.A. 1989. Lake Weir Investigations: completion report, 1984-1989. Florida Game and Freshwater Fish Commission, Central Region, Fish Management Bureau, 1229 SW 10 St., Ocala, Fl. 32674.

3.  Miller, W.R. III, Hendricks, A.C., Cairns, J. Jr. 1983. Normal ranges for diagnostically important hematological and blood chemistry characteristics of rainbow trout (Salmo gairdneri). Can J Fish Aq Sci. 40:420-425.