Synthesis of studies on Comparative brain morphology in Freshwater Fishes in Brazil: a 25-Year Review

The Central Nervous System (CNS) of fishes in Brazil represents an anatomical domain that remains largely underexplored, despite its significant potential to advance phylogenetic, ecological, and behavioral studies. This review synthesizes 25 years (1999-2024) of literature on freshwater fish brain morphology in Brazil, identifying major advancements and persistent knowledge gaps. A total of 16 studies were identified, with a pronounced focus on Siluriformes (62.5%), while other orders outside the Characiphysi clade remain poorly studied. These descriptive and comparative investigations have provided valuable systematic insights, revealed taxonomic characters, and elucidated behavioral and ecological patterns. Despite these contributions, the field faces notable methodological and conceptual challenges. The lack of standardized protocols for brain extraction and analysis hinders consistency and comparability among studies. Furthermore, advanced techniques, such as non-invasive imaging methods, remain underutilized. Critical aspects such as population-level variation in CNS morphology and its responses to environmental pressures have also been largely overlooked. This review underscores the immense potential of comparative brain anatomy to enhance our understanding of biodiversity and evolutionary adaptations in the rich Brazilian freshwater ichthyofauna.