From zero to ossified: Larval skeletal ontogeny of the Neotropical Cichlid fish Cichlasoma dimerus

The identification of skeletal elements, the analysis of their developmental sequence, and the time of their appearance during larval development are essential to broaden the knowledge of each fish species and to recognize skeletal abnormalities that may affect further fish performance. Therefore, this study aimed to provide a general description of the development of the entire skeleton highlighting its variability in Cichlasoma dimerus. Larvae of C. dimersus were stained with alcian blue and alizarin red from hatching to 25 days posthatching. Skeletogenesis began with the endoskeletal disk and some cartilage structures from the caudal fin and the splachnocranium, while the first bony structure observed was the cleithrum. When larvae reached the free-swimming and exogenous feeding stage, mostly bones from the jaws, the branchial arches, and the opercle series evidenced some degree of ossification, suggesting that the ossification sequence of C. dimerus adjusts to physiological demands such as feeding and ventilation. The caudal region was the most variable regarding meristic counts and evidenced higher incidence of bone deformities. In conclusion, this work provides an overview of C. dimerus skeletogenesis and lays the groundwork for further studies on diverse topics, like developmental plasticity, rearing conditions, or phylogenetic relationships.We thank the Laboratory of Entomology and the Laboratory of Amphibian Biology-Animal Histology of the FCEN-UBA for allowing the use of their Leica MZ6 and Leica EZ4D stereoscopic microscopes. Universidad de Buenos Aires (UBACyT 20020190100294BA to P. G. V.), Agencia Nacional de Promoción Científica y Tecnológica (PICT-2018-02577 to P. G. V.). MICIU and the European Social Fund, “The European Social Fund invests in your future” through the Ramón y Cajal (Ref. RYC2018-025337-I to I. F.) contract from the Plan Estatal de Investigación Científica y Técnica e Innovación 2017–2020. 632. This work was carried out with the collaboration of Red CYTED LARVAplus (117RT0521).Peer reviewe