The marine aquarium industry has grown significantly and so has marine ornamental fish aquaculture. The main species targeted by commercial aquaculture are clownfish, dottybacks, gobies, and blennies. However, the limited knowledge available for the reproductive biology of several fish species hinders production, especially for blennies. Therefore, this study investigated whether two massproduced blenniids, Meiacanthus nigrolineatus and Meiacanthus smithi, are gonochorists and display caudal fin sexual dimorphism. For this purpose, gonadal samples and morphometric data were collected from specimens of both species kept in captivity for 6 months. Histological preparations of the whole individuals or their gonads were performed and analyzed. Results show that sex ratio does not differ from 1:1 and that gonadal development was similar to other blenniids. No evidence of sexual reversion or simultaneous hermaphroditism was found in the first 8 months of development, suggesting that both species are gonochoric. Differences in the length of upper and lower rays in the caudal fin were not detected for M. smithi, but M. nigrolineatus male individuals displayed significantly longer upper and lower rays, confirming it as a dimorphic trait for this species. The identification of the sexual pattern and sexually dimorphic traits may aid in broodstock pairing for M. nigrolineatus blennies, improving its aquaculture