Abstract
The process of the testicular maturation of the Japanese sea bass, Lateolabrax japonicus (Cuvier) has been studied. The testis of this species consists of two parts, the hilus of connective tissue (the mediastinum testis) and the stroma in which many seminiferous tubules are located as in the case of most teleosts. After spawning a seminiferous epithelial cell layer becomes distinct along with the wall of the tubule and develops till appearance of the primary spermatogonia in the tubule. This epithelial cell which is regarded as homologous with the Sertoli's cell seems to have those three important roles: i) the decomposition and the resorption of the remaining sperm cells in various maturation stages in the tubule, ii) the original source of the primary spermatogonia, iii) the nutritional supply to the germ cells. The primary spermatogonia come in sight in the tubule from April to August. After mitoses they change into the secondary spermatogonia in the middle of October. Then they rapidly proceed their maturation processes through the meiotic stages. The spermatozoa appear in the tubule for the first time in the middle of November. Based on the microscopical observation the spawning season of this species is guessed to be those two or three weeks between late December and early January in Wakasa Bay.The seasonal change of gonad index closely reflects the histological maturation process, and is useful for judging the maturity. The male of this species takes two years to mature and the biological minimum size of the male is about 260 mm in standard length.
