Abstract This study investigated the population structure of four flatfish species — Achirus lineatus (n = 94), Citharichthys spilopterus (n = 216), Etropus crossotus (n = 104), and Symphurus tessellatus (n = 48) — in the Guaratuba Bay estuary, southern Brazil, along with the reproductive aspects of A. lineatus and C. spilopterus. Monthly sampling was conducted at six sites along the estuary from October 2012 to September 2013. A. lineatus was most abundant in spring and summer, while C. spilopterus and E. crossotus showed population peaks during summer and autumn. S. tessellatus was most common in spring and autumn. Females dominated the larger size classes across all species, with significant differences in sex ratios observed for C. spilopterus and E. crossotus in the mid-estuary zone. Most individuals were captured in intermediate size classes (A. lineatus, C. spilopterus, E. crossotus: 8.9–11.5 cm; S. tessellatus: 11.0–15.1 cm). All species were present across the entire estuarine gradient, except E. crossotus, which was absent from the inner estuary. For the analyzed species, the highest Gonadosomatic Index (GSI) values were recorded during the warmer months. These findings enhance our understanding of flatfish ecology in this estuary and provide essential data to support conservation and management efforts targeting both the environment and flatfish populations.
FÁVARO et al. (Thu,) studied this question.