Egg Production, the Oncomiracidium and Larval Development of Benedenia seriolae, a Skin Parasite of the Yellowtail, Seriola quinqueradiata, in Japan

Abstract

Observations were made on the rate of egg assembly in the capsalid monogenean Benedenia seriolae, a skin parasite of the yellowtail, Seriola quinqueradiata. An adult specimen measuring about 7 mm in length after flattening and preservation, laid 27 eggs in 1h at 20℃. It is suggested that forces exerted on the tetrahedral egg capsule by water currents generated by host swimming, contribute to the stretching of the still soft appendage of a freshly made egg, while it is still tethered to the parasite by the proximal end of the appendage lodged in the uterus. The anatomy of the oncomiracidium is described and an account is given of larval development, based on experimental infection of the related host S. aureovittata. The two anterior attachment discs are absent in the oncomiracidium, but are beginning to develop in post-oncomiracidia recovered one day after infection. The adhesive pads of the oncomiracidium persist on the discs throughout life and their subdivision into three zones is detectable in post-oncomiracidia and in adults. B. seriolae reached full sexual maturity on day 14 post infection (at 22℃).