Variation in the diets of western mosquitofish (Gambusia affinis) in two ponds: effects of time and coexistence with centrarchid fishes

Abstract Western mosquitofish, Gambusia affinis , have been introduced around the world, and can affect native fish through competition and predation. The diet of G. affinis may therefore determine the extent of their interactions with native species. We examined stomach contents of G. affinis from two ponds in central Ohio in 2010, 2015, and 2016. In Olde Minnow Pond, we collected diet data before and after the introduction of the native sunfish, Lepomis megalotis , in 2014. We also collected data for G. affinis for the same period in Wood Duck Pond that has contained G. affinis and Lepomis macrochirus for years prior to the study period. The most important prey were zooplankton, especially Chydorus sp. and Alona sp. Aquatic insects, especially chironomid larvae, were often found in stomachs, with their importance varying by year. The relative consumption of zooplankton increased dramatically in G. affinis , especially females, in Olde Minnow Pond from 2010 to 2015 but then dropped in 2016. In addition, the relative consumption of aquatic insects increased in Olde Minnow Pond after the arrival of L. megalotis compared to 2010. In contrast, the diets of G. affinis in Wood Duck Pond remained relatively similar across the study period. Male and female G. affinis in Olde Minnow Pond had different diets, whereas the diets of males and females in Wood Duck Pond were generally similar. In conclusion, the results of this natural experiment provide circumstantial evidence that the arrival of L. megalotis in Olde Minnow Pond affected the diet of G. affinis .