From that article,
"There are no readily apparent external differences hobbyists can use to differentiate between sexes. In some instances, pairs have been collected from the wild where the male is the larger member, while in other instances it is the female that is the largest. There have been reports (Baensch, 1994) of using the dorsal spine as a means to indicate the sex of the animal, but after reviewing the research data for this species, that would seem a highly unreliable characteristic. For all intents and purposes, there is no way a hobbyist can tell the difference between male and female Stonogobiops while the animal is still alive."