Early sex shape dimorphism (SShD) in Rachycentron canadum (Linnaeus, 1766) and its applications for monosex culture

Rachycentron canadum (cobia) is a species that has attracted the interest of the marine fish farming industry due to displaying numerous traits favorable to cultivation. The species is characterized by its large size, rapid growth, robustness and established technological support for cultivation. Cobia shows sexual size dimorphism (SSD) as adults, with females being significantly larger than males. In fish, sexual dimorphism related to morphology can be the result of ecological, functional, or adaptive selection. Methodologies that allow the application of monosex cultures increase both the biotechnological and production potential of a species. With a view to establishing parameters for early sex determination in R. canadum, morphological analyses were conducted in juveniles aged 139 days (4.6 months) using geometric morphometrics. Sexual shape dimorphism (SShD) in female cobia is expressed by an elongated body and extended space between pectoral and anal fins, suggesting fecundity-related morphological adaptations. The results are promising and indicate a high index of early sex discrimination using geometric morphometrics, demonstrating the possibility of developing routine protocols that can be applied to increase species production.