Reproductive biology of the red cornetfish Fistularia petimba and its relation to fisheries off western Kyushu, southwestern Japan

Abstract The red cornetfish Fistularia petimba (Syngnathiformes; Fistulariidae) is an important commercial fish species caught around all sea areas of Japan, but biological information on the species is limited. In this study, gonadal development of the species was determined, and the spawning season was estimated by the histological observation of gonads using 222 female (691–1783 mm total length without filament) and 120 male (714–1358 mm) specimens caught off western Kyushu (eastern part of the East China Sea), southwestern Japan. The occurrence of vitellogenic oocytes for all females and spermatozoa in all males indicated that they reached sexual maturity. Hydrated oocytes and ovulated eggs in the ovarian cavity were observed from April to October, and the proportion of females possessing them increased from May to July, indicating a spawning season from April to October with a peak from May to July in the area. Postovulatory follicles were exclusively observed with hydrated oocytes or ovulated eggs; however, postovulatory follicles were no longer observed despite ovulated eggs remaining in the ovarian cavity for some females. This suggests that females can retain ovulated eggs until postovulatory follicles degenerate over a few days before they release eggs. The gonadosomatic index increased during the spawning season in females but remained at low values all year-round in males. The small amount of sperm for males even in the spawning season and the retention of ovulated eggs for a few days by females implies some kind of unique reproductive pattern/strategy for the species. Bottom trawl fishery closure during the peak spawning season may contribute to maintaining the stock of the species.