The long-term effects of bluegill Lepomis macrochirus on two Japanese fishes were investigated in two artificial 28 × 22 m concrete ponds. After recording the population size of Japanese minnow Pseudorasbora parva and Amur goby Rhinogobius kurodai in the ponds from 2002 to 2004, 25 mature bluegill were introduced into each. Bluegill successfully reproduced, increasing to 350 fish in pond A and 229 fish in pond B by October, 2004. The population size of the two Japanese species had not varied greatly prior to bluegill introduction, the population size of minnows reaching maximum levels of 7411 in pond A and 1598 in pond B. However, both species decreased after bluegill introduction. By 2015, Japanese minnow numbered 0 and 1 in the respective ponds, indicating functional extinction. Amur goby also decreased after bluegill introduction, but had not been exterminated by 2015.
