Reproduction and Growth of Neobenedenia girellae(Monogenea: Capsalidae), a Skin Parasite of Cultured Marine Fishes of Japan.

Abstract

Under laboratory conditions at 25°C, the monogenean Neobenedenia girellae (Hargis, 1955) rapidly developed on Japanese flounder (Paralichthys olivaceus), and it took 15-17 days from egg to maturation.The whole process of egg formation from the release of oocytes from the germiduct to laying of egg capsule required a mean of 73sec. At room temperatures between 27-30°C, large adults laid a mean of 35.4eggs/h, while smaller ones a mean of 12.2eggs/h. Eggs began to hatch after incubation for 5-6 days at 25°C with natural cycle of illumination, but no hatching occurred at 15°C. It took 10-11 days to reach sexual maturity where the minimum body size for an egg-laying adult was 2.1mm. When compared with other benedeniine species, N.girellae required a shorter time and a smaller body size to attain maturity and showed a high level of egg output. One-day old larvae were found only on the fins of Japanese flounder.As the parasites grew, they were found not only on the fins but most commonly on the dorsal and ventral body surface of fish, suggesting migration of the parasite from the fins.