Neuroanatomical diversity in Teleocichla with new volumetric and histological insights into the encephalon of Teleocichla monogramma Kullander 1988.

Teleocichla comprises small cichlids that inhabit the rapid streams of Amazonian rivers; however, there has been limited research on their encephalon morphology. This study examined the neuroanatomy of four species, focusing on volumetric measurements of their encephalon subregions, and providing a histological description of the encephalon of T. monogramma. Our findings reveal that the tectum mesencephali and torus semicircularis have the highest relative volume across all species examined, followed closely by the telencephalon and ventral diencephalon. The tectum mesencephali in some species of Teleocichla reached the highest recorded values for neotropical cichlids. The encephalic mass to body mass ratio calculated for the investigated species indicates a level of encephalization similar to that typically observed in taxa with smaller adult body sizes. We assert that these morphological similarities, alongside the pronounced volume of their visual centers, are indicative of their biology, diurnal habits and habitat preferences in complex environments such as clear-water rapid streams. This research significantly enhances our understanding of the morphological diversity of the Teleocichla encephalon and establishes new histological insights into the encephalon of the neotropical cichlids.