Environmental effects and metabolic regulation in juvenile Selenotoca multifasciata: experimental assessment across temperature, salinity and pH gradients.

Environmental factors such as temperature, salinity and pH influence oxygen consumption and nitrogen excretion in juvenile Selenotoca multifasciata. This study used intermittent-flow respirometry to evaluate the effects of temperature, salinity and pH on oxygen consumption rate (OCR), ammonia excretion rate (AER), O:N ratio, PEP and asphyxiation point in juvenile S. multifasciata. Temperature affected both OCR and AER, with the highest values recorded at 36 °C within the tested range, while the asphyxiation point also increased with temperature. Salinity effects were non-linear: OCR was highest at 15‰, AER remained comparatively low at 5-20‰ and increased markedly at 25‰, and the asphyxiation point was lowest at 10‰. pH effects were also non-linear: OCR was highest at pH 6.0 and lowest at pH 6.5, AER reached its highest value at pH 8.0, and the asphyxiation point was lower at pH 7.5-8.0 than at pH 6.0 and 9.0. These results show that juvenile S. multifasciata exhibited treatment-specific metabolic responses under short-term single-factor exposures. Within the present experimental context, 24-28 °C, 10-20‰ salinity and pH 7.5-8.0 were associated with comparatively lower oxygen-consumption/nitrogen-excretion burden or lower oxygen values at the measured asphyxiation endpoint. These ranges should be interpreted as experimental associations rather than validated optima for growth, performance or survival.