The Combined Effects of Temperature and pH to the Toxicity of the Water-Soluble Fraction of Gasoline (WSFG) to the Neotropical Yellow-Tail Tetra, Astyanax altiparanae

Continental aquatic environments have undergone chemical pollution due to increased anthropogenic activities. Among those substances, petroleum hydrocarbons are a potential hazard for the aquatic animals. Additionally, alterations in the abiotic characteristics of the water, such as temperature and pH, can impose additional stress when those substances are present. We evaluate how alterations in water temperature and pH modified the acute (96 h) toxicity of the water-soluble fraction of gasoline (WSF_G) to Astyanax altiparanae through physiological analysis. We also investigated the physiological responses after the fish recovery from exposure (96 h) in clean water. Both isolated and combined exposures to WSF_G resulted in significant physiological changes. Alone, WSF_G altered energetic metabolism and haematopoietic functions, potentially due to metabolic hypoxia. When combined with changes in water temperature (30 °C) and pH (4.0), A. altiparanae activated additional physiological mechanisms to counterbalance osmoregulatory and acid–base imbalances, likely exacerbated by severe metabolic hypoxia. In both isolated and combined exposure scenarios, A. altiparanae maintained cellular hydration, suggesting a robust capacity to uphold homeostasis under environmental stress conditions. Following a recovery in clean water, energetic metabolism returned to control levels. Nevertheless, plasmatic Na⁺ and Cl⁻ levels and haematological parameters remained affected by WSF_G exposure. Our findings underscore the impact of interactions between WSF_G contaminants, temperature and pH, leading to additional biological damage in A. altiparanae.