Natural Sex Inversion in the Giant Perch (Lates calcarifer)

Abstract

A detailed examination of the sexuality of L. calcarifer led to the conclusion that it was a protandrous hermaphrodite. The smaller length classes are almost exclusively male, the percentage of females increasing with increased total length. Length frequencies, calculated from the dissection of 5202 mature specimens, give a male mode at 89.5 cm and a much smaller female one at 101.5 cm. The overall sex ratio is 3.8:1 in favour of males. There is a small proportion of primary females and also the possibility that some males do not undergo the change to female. Biopsy experiments were used to confirm protandric sex inversion.

As the gonads of L. calcarifer are strongly dimorphic, inversion of sex requires a complete reorganization of gonad structure as well as function. Few hermaphrodite gonads were detected, this being attributed to a rapid transition phase from male to female and the lack of sampling during the period when transitions are most likely to occur.