Human harvesting such as hunting and fishing brings additional mortality to ecosystems. However, harvesting mortality is highly selective, and it often causes unnatural change in the life history traits of exploited animals. In fisheries especially, intentionally or unintentionally, fishing often selects only male or female. Since the operational sex ratio (OSR, the ratio of males to females that are ready to mate) directly affects mating behaviour and population dynamics, harvested animals would consequently suffer a burden in their need to respond to the artificially-created skew in OSR. However, there is less information on how the sex-biased selection shapes the life history of exploited animals. We describe a concrete example of plastic sex-ratio adjustment by a male-first sex-change shrimp exposed to unintentional female-selective fishing. The OSR adjustment by shrimp did not always seem to be sufficient, however, as the supplement of females resulting from early sex-change by annual somatic growth rates. Consequently, a genetic downsizing in their size at sex-change occurred to adjust OSR.