Common snook reproductive physiology in freshwater and marine environments of Mexico

ABSTRACT The common snook (C. undecimalis) is a highly valuable commercial and sport fishing species in marine, estuarine, and freshwater habitats. Despite its abundance in freshwater ecosystems, the information on the reproductive biology comes mainly from studies in the marine habitat. In this work, the reproductive cycle at the gametogenic and hormonal level is addressed in specimens captured in contrasting environments interconnected by the Grijalva-Usumacinta fluvial system. Adult common snook presented a similar temporal pattern in sex steroid concentrations in both environments. Likewise, females and males were observed undergoing advanced maturity simultaneously in both environments. However, females in the freshwater environment did not reach final maturation, and no post-ovulatory follicles were found, indicating that spawn did not happen. Therefore, organisms are synchronized with gonads developing in both habitats, implying migrations of at least 300 km from the freshwater environment to the spawning grounds in the Gulf of Mexico.