Complete life cycle of a pennellid Peniculus minuticaudae Shiino (Copepoda: Siphonostomatoida) infecting cultured threadsail filefish

Abstract

Peniculus minuticaudae Shiino is a parasitic copepod infecting fins of fishes mainly belonging to the family Monacanthidae. Recently it seems to have been spreading in fish farms in western Japan and southern Korea. Our study showed the infection occurs all year round with the highest intensity recorded during summer. Based on our finding of all post-embryonic stages together with the post-metamorphic adult females on the fins of threadsail filefish Stephanolepis cirrhifer Temminck and Schlegel cultured in a fish farm at Ehime Prefecture, Japan, we newly proposed the complete life cycle of P. minuticaudae. The hatching stage was observed as an infective copepodid. It metamorphosed into chalimi I to IV after infection on fins. Sex can be differentiated from chalimus I. Adult males were observed frequently in precopulation amplexus with various stages of chalimi, however, copulation occurs only between adults. Fertilized pre-metamorphic adult females carrying paired spermatophores may detach from the host, and settle again on the same host and site to undergo massive differential growth to become post-metamorphic adult. A comparison of the life cycle of P. minuticaudae has been made with those of three known pennellids Lernaeocera branchialis Linnaeus, Cardiodectes medusaeus Wilson and Lernaeenicus sprattae Sowerby. The life cycle of pennellids can be divided into four categories based on the number of hosts and the ection occurs all year round with the highest intensity recorded during summer. Based on our finding of all post-embryonic stages together with the post-metamorphic adult females on the fins of threadsail filefish Stephanolepis cirrhifer Temminck and Schlegel cultured in a fish farm at Ehime Prefecture, Japan, we newly proposed the complete life cycle of P. minuticaudae. The hatching stage was observed as an infective copepodid. It metamorphosed into chalimi I to IV after infection on fins. Sex can be differentiated from chalimus I. Adult males were observed frequently in precopulation amplexus with various stages of chalimi, however, copulation occurs only between adults. Fertilized pre-metamorphic adult females carrying paired spermatophores may detach from the host, and settle again on the same host and site to undergo massive differential growth to become post-metamorphic adult. A comparison of the life cycle of P. minuticaudae has been made with those of three known pennellids Lernaeocera branchialis Linnaeus, Cardiodectes medusaeus Wilson and Lernaeenicus sprattae Sowerby. The life cycle of pennellids can be divided into four categories based on the number of hosts and the