Reproductive traits, sex-specific reproductive investment and gonadal dynamics in a spawning surgeonfish

The razor surgeonfish Prionurus laticlavius is a key herbivore in Eastern Pacific reef communities. This study provides a sex-specific assessment of its reproductive traits, size at maturity and energetic dynamics in the Gulf of California by integrating biometric indicators (adult sex ratio, TL₅₀), somatic indices (hepatosomatic index, HSI; visceral fat index, VFI; gonadosomatic index, GSI) and histological analyses of gonadal development stages (GDS). Monthly sampling over one year revealed a female-biased adult sex ratio and a larger size at maturity (TL₅₀ = 35.1 cm) than males (TL₅₀ = 33.3 cm). Reproductive investment, as measured by GSI, showed a relay-like asynchronous alternation between sexes. Histologically mature males exhibited the highest GSI values (around 3.4%) from August to October, exceeding those of females. Conversely, from November through July, both sexes remained histologically mature at GSI values below 1%, with females dominating during this period. The relative gonadal expenditure between sexes (RGES: logarithm of the ratio males-to-females GSIs) confirmed that each sex contributed differentially to reproduction across the annual cycle, complemented by energetic strategies where females showed higher HSI and VFI than males. Sex-specific correlations between somatic indices and GSI suggested divergent physiological pathways between sexes. Histological GDS analyses revealed in males two to four stages per month, whereas females exhibited between one to three stages. Melanomacrophages increased during regressing and regenerating stages, with sex-specific peaks associated with tissue turnover and post-spawning recovery. Together, these sex-specific strategies indicated that reproductive investment in P. laticlavius is driven by differences in physiological demands and timing, shaping the annual reproductive dynamics.