Sex Differentiation, Sexual Maturity and the Spawning Season of the Red Tilefish Branchiostegus japonicus on the Pacific Coast of Tokushima Prefecture

Abstract

The one year-old red tilefish Brachiostegus japonicus (smaller than 20cm in total length (TL)) possesses an intersexual gonad, in which primary oocytes and spermatogonia are observed. Thereafter, the gonad differentiates into either an ovary or testis. In the ovary, spermatogonia disppear and oocytes markedly increase in size and number, whereas in the testis, oocytes, although decreasing and degenerating, are observed to remain long. Most males over three years old (larger than 30cm in TL) possess a complete testis.
Gonadal maturation is observed to occur from late May through late October in females, and from mid-May through late January in males. The biological minimum size is 21.4cm TL in females and 23.7cm TL in males. Most females and males mature at two and three years-old, respectively.