Induction of sex ratio change and intersex in Tegillarca granosa (Bivalvia: Arcidae) by waterborne zinc exposure

•The effect of zinc on the change in sex ratio and intersexuality have been described during the gonadal inactive stage of Tegillarca granosa.•T. granosa exposed to zinc showed tendency to increase the proportion of males in a concentration-dependent manner.•Intersexuality increased with an increase in zinc concentration, and occurred more in female than male groups.•The intersex type was histologically classified interfollicular and intrafollicular types.•Such finding indicate a zinc acted as androgenic effectors. This study aims to investigate the effect of zinc on the sex ratio and intersexuality of Tegillarca granosa, a sequential hermaphroditic bivalve that undergoes sex change during the gonadal inactive stage. Groups of T. granosa in the gonadal inactive stage were first exposed to zinc under indoor aquarium conditions for 5 weeks, and then under wild conditions for 3 months. The proportion of males and females tended to increase and decrease, respectively as the zinc concentration increased. Intersexuality increased with an increase in zinc concentration, and occurred more in female than male groups in all zinc exposed groups. The intersex of T. granosa exposed to zinc could be divided into interfollicular and intrafollicular types according to the histological pattern. The results of this study suggest that zinc exposure higher than a certain concentration may induce male sexuality during the gonadal inactive stage in the same population of T. granosa, and could result in unequal sex ratios as well as intersex.