Countertactics of the Japanese aucha perch Siniperca kawamebari against brood parasitism by the Japanese minnow Pungtungia herzi

Japanese aucha perch males taking care of eggs and fry are often brood-para sitized by a Japanese minnow. When the minnows are ovipositing in the perch nests, some of the perch eggs in the nests are often eaten by other fishes . The minnows' eggs are subsequently guarded by the perch males until hatch ing. Countertactics of the perch against such brood parasitism were examine d in a river of western Japan. Perch males did not employ any countertactic s such as ejection of parasites' eggs or nest desertion. On the other hand, perch females avoided spawning in nests with greater numbers of perch eggs and produced smaller clutches during the parasitic period than in the non- parasitic period. These behavior can be regarded as anti-parasitism tactics because minnows prefer to spawn in nests with higher numbers of perch eggs .