Feeding Behavior Changes of Juvenile Bluegill Lepomis macrochirus Due to Ingesting Red Imported Fireants Solenopsis invicta
The red imported fire ant Solenopsis invicta (fire ant) was introduced to the United States in the mid 1930’s and has become established as a pest throughout the southeastern United States. The fire ant has had a negative impact on many native species. Surprisingly, the fire ant has been implicated in fish kills in the southeastern United States since the 1960’s. Fire ants can enter the water column either by flood events or by flight associated with mating behavior. The fire ant venom associated with their sting is toxic to fish. The purpose of this study was to determine if fire ants are acutely toxic to juvenile bluegill Lepomis macrochirus and to determine if juvenile bluegill learn to avoid ingesting fire ants. Fifty five juvenile bluegill (66 ± 5mm (TL); 4 ± 1g) were collected from a local farm pond and equally distributed among 11 30L glass aquaria maintained at room temperature (22.4 °C). Each aquaria was fitted with a cover and a sponge filter that provided constant aeration and maintained water quality. Two tanks served as controls and nine tanks served as treatment replicates. All fish were conditioned to feed on a commercially available floating pellet within 5 d by turning off the aeration and removing the cover. For the first fire ant feeding, all treatment tanks were offered an unlimited amount of fire ants for 20 minutes and the control tanks were offered the usual floating pellets. The number of fire ants ingested per tank was enumerated. For the second fire ant feeding two d later, the same protocol as the first feeding was followed. All fish were fed floating pellets between fire ant feeding trials. There were no mortalities recorded for control or treatment tanks. Fish in the control tanks ingested a similar number of pellets on days that the treatment tanks were offered fire ants. There was a significant difference between the number of ants ingested between the first and second feeding (figure 1). Finally, fish in the treatment tanks actively fed on the floating pellets between the fire ant feeding days. Although no mortalities occurred during this study, it is clear that juvenile bluegill quickly learn to avoid ingesting fire ants.