Hepatic response of male Astyanax lacustris (Characiformes: Characidae) to long-term exposure to elevated water temperatures

The average global temperature has increased significantly in recent decades due to anthropogenic activities. In aquatic environments, rising temperatures act as a major thermal stressor, affecting fish growth and development. However, little is known about the effects of elevated temperatures on the liver tissue of Astyanax lacustris , a species of importance in aquaculture. Thus, this study investigated the effects of high temperature (32 °C) and exposure duration on liver histopathology in A. lacustris . Forty males were maintained in a recirculating aquaculture system under two temperatures (26 °C and 32 °C) and evaluated after 30 and 210 days of exposure. Histopathological alterations such as leukocyte infiltration, cytoplasmic vacuolization, and hyperemia were observed at low frequencies, associated with both exposure time and elevated temperature. Vascular congestion, a more severe condition that can compromise liver function, was not directly related to temperature increase; however, it was associated with the reproductive period. The histopathological index indicated mild to moderate damage at 26 °C after 30 days, whereas normal hepatic function was preserved in all other groups. Overall, the low incidence and severity of lesions indicate that A. lacustris can maintain liver integrity when exposed to temperatures up to 32 °C in recirculating water systems. These findings suggest a degree of hepatic resilience to warming conditions, although longer-term exposure may increase the risk of tissue alterations, highlighting the need for further investigations under climate change scenarios.