Most behavioral studies on hermaphroditic fishes have focused on small-sized species, which are tractable for research. Although many species of large hermaphroditic fishes are important fishery resources, their proximate mechanisms (visual, chemical and/or behavioral cues) in the social regulation of sex change have not been determined. Determination of these would inform resource management and aquaculture. In order to get closer to understanding the proximate mechanisms underlying the social regulation of female-to-male sex change in large hermaphroditic fishes, this study reports situations that induced female-to-male sex change in black-spot tuskfish, Choerodon schoenleinii, a species of large protogynous fish, in massive laboratory tanks. The situations differed in the possibility of male-to-female tactile contact and in the group sex ratio, enabling us to infer plausible proximate mechanisms underlying sex change induction. Tactile contact between individuals is suspected to be closely related to the incidence of female-to-male sex change in C. schoenleinii. Visual and chemical cues alone may be insufficient to inhibit such sex changes. Male-to-female tactile contact may have an important influence on female-to-male sex change, i.e., inhibition of this sex change, in this species. The effect of sex ratio of a social group on the incidence of sex change may be due to the relative frequency and intensity of male tactile contact with each female, which may vary with the number of females. In the absence of a dominant male, tactile contact among females may affect the incidence of sex change, as well as determine which individuals change sex.