Effects of Ingesting Red Imported Fire Ants on Fishes

Q.C. Fontenot, J.J. Isely, and C.R. Allen
U.S. Geological Survey, Biological Resources Division, South Carolina Cooperative Fish and Wildlife Research Unit, Clemson University, Clemson, SC 29634-0372

The red imported fire ant Solenopsis invicta has become established throughout the southeastern United States since being introduced to this country in the mid 1930's. It is considered a nuisance and has been implicated in numerous fish kills. We conducted a number of experiments to determine if ingesting fire ants has a negative impact on fishes. Small (36 + 5.9 mm; 0.4 + 0.27 g) and large (59 + 7.5 mm; 1.7 + 0.53 g) yellow fin shiners Notropis lutipinnis and rainbow trout Onchorhynchus mykiss ( 106 + 12.3 mm; 11.9 + 3.72 g) were twice fed fire ants ad libitum with a 3-d period between feedings. Large yellowfin shiners ingested fewer fire ants the second feeding than the first feeding. We recorded 4% mortality for both small and large test yellowfin shiners and 0% mortality for control fish. Rainbow trout also avoided ingesting fire ants after one exposure. No mortalities were recorded for test or control rainbow trout. To expose fish in a more natural manner, a large floating ball of fire ants was offered twice with a 5-d interval to tilapia Oreochromis niloticus maintained in flow-through raceways. Fish were allowed to eat fire ants for one hour, then twenty fish from each replicate (N=3) were removed, euthanized, and frozen. Presence of fire ants in the gasto-intestinal tract did not differ between feedings. No mortalities were recorded for test or control fish. Our laboratory is currently conducting similar experiments with bluegill Lepomis macrochirus and green sunfish L. cyanellus.