養殖クロダイに寄生するAlella macrotrachelusの生活史

Recently, industrial farming of black sea-bream, Acanthopagrus schlegeli (Bleeker), has grown prosperous in the Inland Sea of Japan. This species is said to be fairly resistant to environmental water pollution and diseases as compared with yellow tail, Seriola quinqueradiata, a popular species in mariculture of our country. However, some ectoparasites are known to attack cultured black sea-bream. Among them, Alella macrotrachelus (Brian, 1906) (Copepoda: Lerneopodidae) with which we deal here seems to be the most harmful gill parasite.

In this paper the development of this parasite is described, based on specimens from laboratory experiments.

The female life cycle proved to consist of seven stages; one nauplius stage, one copepodid stage, four chalimus stages (attached by frontal filament), and the adult stage (attached by bulla). The life cycle of the male could not be revealed thoroughly, but it is clear that the male gets into the life of superinfection on the female at its second chalimus stage. Sexual dimorphism becomes distinct in the second chalimus stage.