The goby Lythrypnus pulchellus is a bi-directional sex changer

Sex change in both directions is a novelty reported in some species of fishes belonging to seven families associated to reefs. This study demonstrated that Lythrypnus pulchellus, a small cryptobenthic haremic reef fish, is a bi-directional sex changer, at least in experimental conditions. The influence of body size in duration and direction of sex reversal was tested, and the changes of sexual dimorphic traits (elongated anterior dorsal spine, genital papillae, body size) and sex-cell allocation in the gonad during sex change were described. Unisex pairs of individuals, male-male and female-female of similar and different body size, were housed in aquaria recording the changes until spawning. Sex change duration showed no significant differences between protogyny (11 days) and protandry (12 days), regardless of their size. Among pairs of males of different size, the smaller individual changes sex to female whilst among pairs of females of different size larger individuals change sex to male. Among pairs of males of similar size, dominant individuals remained as male whilst subordinate individual did change sex to female. If the pair of similar size were females, the dominant individual changed sex to male whilst the subordinate remained as female. The gonads, before, throughout, and after sex change, showed that females and males contained both ovarian and testicular tissues in different ratios. The length/width ratio of the genital papilla probed to be useful to predict functional sex of individuals. The results support the idea that extreme sexual plasticity is a widespread reproductive trait in the genus Lythrypnus.