Can otoliths of Genidens genidens (Cuvier 1829) (Siluriformes: Ariidae) reveal differences in life strategies of males and females?

Determination of the growth parameters of a species is an indispensable requirement for understanding its biology and consequently the management of its fishery. In fisheries science, calculations of longevity, mortality rates and stock-assessment models depend on the availability of growth data. Genidens genidens, one of the most common ariid species in Brazil, is a potential sentinel species for biomonitoring in Guanabara Bay, one of the country’s most degraded estuarine ecosystems. The present study investigated the growth parameters of G. genidens, providing supporting information for its management. Individuals were measured, sexed, and the number of rings in the lapillus otolith counted. The periodicity in the formation of the rings was determined by the monthly ratio of the edge type. Individuals from 0 to 11.5 years old were captured, including some that were older than previously reported. Our results showed that this species forms two growth rings per year, one in summer and the other in winter; the summer ring is formed one month later in males than in females, due to the period of oropharyngeal incubation of the offspring. Sexual dimorphism was also observed in the growth rate: males grow faster, and consequently reach smaller sizes than females. We can conclude that the parental care carried out by males and the high energy expenditure in forming the large oocytes by females mark the otoliths and reveal life-cycle particularities differently in each sex.