Otolith and vertebral morphology of marine atherinid species (Atheriniformes, Atherinopsidae) coexisting in the southwestern Atlantic Ocean
Studies on marine ecosystems rely on the identification of fish prey species of piscivores (fish, aquatic mammals, and aquatic birds) based on their bones and otoliths. The stomach contents of piscivores show predation on marine atherinids of commercial value; however, their identification is difficult due to the coexistence of these species. The objective of the present study is to propose the use of hard structures (otolith, caudal vertebrae) as a tool for the identification of marine atherinid fishes occurring in the southwestern Atlantic Ocean. Sagittae (200 pairs) were removed from the otic capsules for further examination and measurement. The vertebral column of individuals from each species was also removed for examination. The morphological pattern of the sagitta otoliths of five marine species belonging to the genus Odontesthes was consistent with that of the subfamily Atherinopsinae, with these patterns being species specific. In Odontesthes argentinensis, O. platensis, and O. smitti, the caudal vertebrae present an expansion of the haemal arch walls forming a haemal funnel with distinctive morphology, while this characteristic is absent in O. incisa and O. nigricans. The hard structures used in this study proved to be a useful tool for the correct identification of the atherinids found in the diet of piscivorous species from the southwestern Atlantic Ocean. A key based on the major morphological features of sagittae and hemal arches is provided.