Hermaphroditism in Cultured Chinese Black Sleeper (Bostrichthys sinensis L.)

Anatomical studies showed that all collected feral fish of Chinese black sleepers (Bostrichthys sinensis L.) were gonochoristic. In contrast, an average of 12.4% of cultured fish appeared to be hermaphroditic. The shape of the genital papilla of hermaphroditic specimens resembled that of gonochoristic males. The gonadosomatic index (I_G) of hermaphroditic fish varied from 0.24 to 4.48%, while that of gonochoristic conspecifics varied from 6.1 to 12.2% for females and 0.11 to 0.14% for males. Histological studies revealed that the sex organs of hermaphrodites consisted of ovarian, testicular, and seminal vesicle tissues, located in the central, peripheral, and caudal region of the gonads, respectively. During the spawning season, ovarian tissue contained poorly developed oocytes, that is, hydrated oocytes were absent and only a few degenerated vitellogenic oocytes were present. Testicular tissue, however, contained fully developed spermatozoa. The fertilization rate of these spermatozoa was significantly lower than those of gonochoristic conspecifics. It is concluded that part of the cultured stock of Chinese black sleeper became hermaphroditic during culture and that the hermaphrodites are able to function as males. The lowered fertilization rate, however, indicates that hermaphroditism in cultured fish of this species is disadvantageous to reproduction.