Nobuhiko Akiyama

Stages of Embryonic Development of the Ice Goby (Shiro-uo), Leucopsarion petersii

Abstract A series of normal stages for the embryonic development of the ice goby (shiro-uo), Leucopsarion petersii, which belongs to the Perciformes, is described. Stages are based on morphological features, by utilizing the optical transparency of live embryos from the first cleavage to the hatching stage. Fertilized eggs were obtained by artificial insemination and normal embryogenesis was accomplished in a defined medium in plastic petri dishes at 19°C. Shiro-uo eggs were surrounded by a very thin and clear chorion and could be dechorionated with forceps very easily. Developmental stages were mostly comparable to those of other fish embryos described so far, but several differences were indicated, such as the third cleavage plane being horizontal, and that the length of the cleavage cycle increased gradually from the very early stages. Also, there were differences in the relative rates of organogenesis of the brain, eyes, otic vesicles, and somites when compared to the zebrafish and medaka.

Annual Reproductive Cycle of a Bitterling, Tanakia tanago, Reared in an Outdoor Tank

Abstract From June 2000 to September 2001, we investigated the presence of eggs spawned in Margaritifera laevis and the seasonal changes in the gonads of Tanakia tanago. Eggs were observed from mid-March to mid-September. In females with a shrunken ovipositor, as the GSI gradually increased, most ovaries were in the prespawning phase (Oct–Mar). As the GSI increased further, most ovaries were in the early spawning phase (Mar–Jun). As the GSI gradually deceased, ovaries in the late spawning phase appeared (Jun–Sep). When the GSI was very low, most ovaries were in the postspawning phase (Sep–Oct). In males, when the GSI was low, most testes were in the early prespawning phase from Oct–Dec. As the GSI gradually increased, most testes were in the late prespawning phase (Dec–Jan). As the GSI increased further, testes were in the early spawning phase (Jan–Jun). As the GSI gradually decreased, amost testes were in the late spawning phase (Jun–Sep). When the GSI was very low, most testes were in the postspawning phase (Sep–Oct). These results indicate that T. tanago has a distinct annual reproductive cycle and is a spring–autumn spawner. Based on the relationship between reproductive activity and environmental factors, the spawning season of T. tanago appears to be initiated by increasing temperature and / or longer days in spring and to be terminated by shorter days in autumn.