Diet composition of post-metamorphic bullfrogs(Rana catesbeiana)in the Zhoushan archipelago,Zhejiang Province,China

Bullfrogs(Rana catesbeiana)are listed as one of the 100 worst invasive alien species in the world.They are generalist predators and thus may affect native species through predation.In previous studies,the food contents of bullfrogs were mostly examined at a single site.In the present study,the diet composition of post-metamorphic bullfrogs on eight islands(Daishan,Liuheng,Xiushan,Fodu,Taohua,Xiashi,Cezi,and Putuoshan)in the Zhoushan Archipelago,Zhejiang Province of China,were examined by using the stomach flushing method from June 30 to August 11 in 2005.A total of 391 individual frogs were measured,including 113 adults and 278 juveniles.The analysis of the stomach contents shows that,for adult bullfrogs,the most important prey(by diet volume)overall were Decapoda,Coleoptera,Odonata,Mesogastropoda,Raniformes,and Cypriniformes.For juvenile bullfrogs,these were Decapoda,Coleoptera,Cypriniformes,Odonata,Orthoptera,Hymenoptera,Lepidoptera larvae,Mesogastropoda,and Raniformes.Moreover,the prey size and diet volume increased with the body size of both adult and juvenile bullfrogs.The diet composition of primary preys of bullfrogs was significantly different among the islands.The results indicate that bullfrogs exert different predatory influences on native fauna at different sites and that bullfrogs are generalist predators with extensive ecological impacts on native fauna.