Salinity, Temperature and Ammonia Acute Stress Response in Seabream (Sparus aurata) Juveniles: A Multidisciplinary Study

SIMPLE SUMMARY: Gilthead seabream (Sparus aurata) is a teleost fish of great relevance in marine aquaculture, especially in the Mediterranean area and one of the most important farmed food marine species in Europe. Nevertheless, in captivity fish are usually exposed to stressful conditions, with a consequent negative impact on animal welfare and growth. The principal goal of this study was to shed light on the acute stress response of gilthead seabream juveniles exposed to different stressors using a multidisciplinary approach. For this purpose, gilthead seabream have been exposed to three different stress tests (temperature, salinity, and ammonia changes) and several laboratory techniques have been used to evaluate their growth and stress response. Results revealed that all the tested stressors had an impact on fish growth and health, particularly thermic and chemical exposure, whereas salinity seems to have a minor effect since this species can efficiently face with extreme variations in environmental salinity. The present work aimed to obtain relevant information on acute stress response of gilthead seabream to be used for improving farming condition and ensuring fish welfare. ABSTRACT: The present study aimed to investigate the acute response of gilthead seabream (Sparus aurata) juveniles exposed to temperature, salinity and ammonia stress. Radioimmunoassay was used to evaluate cortisol levels, whereas insulin-like growth factors (igf1 and igf2), myostatin (mstn), heat-shock protein 70 (hsp70) and glucocorticoid receptor (gr) gene expression was assessed trough Real-Time PCR. The presence and localization of IGF-I and HSP70 were investigated by immunohistochemistry. In all the stress conditions, a significant increase in cortisol levels was observed reaching higher values in the thermic and chemical stress groups. Regarding fish growth markers, igf1 gene expression was significantly higher only in fish subjected to heat shock stress while, at 60 min, igf2 gene expression was significantly lower in all the stressed groups. Temperature and ammonia changes resulted in a higher mstn gene expression. Molecular analyses on stress response evidenced a time dependent increase in hsp70 gene expression, that was significantly higher at 60 min in fish exposed to heat shock and chemical stress. Furthermore, the same experimental groups were characterized by a significantly higher gr gene expression respect to the control one. Immunostaining for IGF-I and HSP70 antibodies was observed in skin, gills, liver, and digestive system of gilthead seabream juveniles.