Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056, Japan
Population biological aspects of the macrourid fishes (Gadiformes) have not been sufficiently examined yet. The reproductive biology of the grenadier Coelorinchus jordani (Macrouridae) was studied using a large number of specimens which were collected in Kagoshima Bay, at 115-227 m in depth, by a commercial bottom trawler. Ovarian maturity stages were divided into three categories based on macroscopic visual examination of ovaries: stage I (undeveloped: oocytes invisible), stage II (early ripe: oocytes visible but not hydrated) and stage III (ripe: presence of hydrated oocytes). The size at sexual maturity of females was estimated to be 35 mm in pre-anal length. In the present study, females with stage-III ovaries which contained the hydrated oocytes were defined as mature females. Based on the seasonal changes in the gonado-somatic index and occurrence of the mature females, the spawning season of C. jordani was estimated to continue almost all year round with its minor peaks in spring and autumn. Percentage occurrence of mature females tended to be higher in the shallow area (less than 200 m in depth) than the deep area (above 200 m in depth) in the bay.