Does telencephalic lateralization modulate anxiety? Effects of unilateral ablation assessed in the light-dark and open field tests in Nile tilapia (Oreochromis niloticus)

Functional brain lateralization is widespread among vertebrates, including teleost fish, and plays a key role in emotional regulation, particularly in anxiety. However, the contribution of each telencephalic hemisphere to anxiety-like behavior remains poorly understood in most fish species. This study investigated whether unilateral telencephalic ablation affects anxiety-like responses in Nile tilapia, a species of ecological and economic relevance that is increasingly used in neurobehavioral research. Eighty-four fish were assigned to four groups: left ablation, right ablation, sham-operated, and intact controls. After behavioral performance was assessed using the light-dark test (n = 37) and the open field test (n = 35). Telencephalic ablation did not alter preference for the dark compartment; however, fish with right-hemisphere ablation showed increased avoidance of the light compartment, suggesting a potential lateralized contribution to threat evaluation. Across repeated exposures, freezing and erratic swimming decreased in all groups, including those with ablations, indicating preserved habituation despite telencephalic damage. In the open field test, no group differences were detected in freezing, thigmotaxis, or spatial distribution, although erratic swimming was more frequent in ablated animals, with the left-lesioned group differing significantly from both control groups. Overall, these findings indicate that telencephalic lateralization in Nile tilapia does not exclusively govern anxiety-like behavior but may influence specific components, such as light avoidance and motor reactivity. The preserved habituation and subtle lateralized effects highlight compensatory neural plasticity and the involvement of extra-telencephalic circuits. This study provides new evidence for emotional lateralization in teleost and reinforces the value of Nile tilapia as a model for investigating the neural basis of lateralized emotional processing.