Description of Encephalon Morphology of Nile Tilapia Oreochromis niloticus (Linnaeus, 1758) (Perciformes: Cichlidae) From Brazil.

The Nile tilapia (Oreochromis niloticus) is a cichlid species native to Africa and is widely farmed in tropical and subtropical regions around the world, making it one of the most commercially important aquaculture species. Despite its significance, there is still a lack of detailed anatomical descriptions of its brain. This study aimed to provide a comprehensive anatomical and histological characterisation of the O. niloticus brain. Brain samples were collected from adult fish (n = 19) raised in a commercial aquaculture system in Brazil. The brain morphology of O. niloticus exhibits the general organisational pattern typical of teleosts, featuring two olfactory bulbs at the most cranial part of the brain, followed by prominent telencephalic lobes, a mesencephalon with a well-developed pair of optic tectum, a ventrally located diencephalon with two large paired inferior lobes of the hypothalamus, a prominent cerebellum, and a large medulla oblongata. The gross and internal anatomy closely resembles that of other species within the same genus, such as Oreochromis mossambicus, as well as other cichlids and related teleosts, demonstrating a high degree of morphological similarity. In contrast, notable neuroanatomical differences are observed in more distantly related groups, such as Siluriformes and Gymnotiformes. Understanding the macroscopic and microscopic features of the brain can contribute to future studies in reproductive biology, behaviour, and systematics.