Long-term effects of temperatures on the physiological response of juveniles of the eurythermal sub-antarctic notothenioid Eleginops maclovinus

Eleginops maclovinus is a subantartic notothenic with eurythermal characteristics and potential for Chilean aquaculture. However, the information regarding their physiological response to long-term temperatures and optimum temperature range for physiological process is unknown. In the present study, we evaluated under experimental conditions, the long-term effects (60 days) of temperatures of 15 °C and high temperatures of 20 and 25 °C, (10 °C as control) on the physiology of E. maclovinus juveniles. At the end of the experimental period, survival was 36% at 25 °C and mortality started after 30 days, while at the other temperatures the survival was 100%. The growth and food intake did not present significant differences at 10, 15 and 20 °C, while at 25 °C growth decreased at day 15, to subsequently present a compensatory growth at day 30 and finally a decrease in growth and food intake at day 60. In general, the energy substrates in liver, gills, serum, and spleen showed a significant decrease at 25 °C, with a marked decrease in triglycerides, while white muscle presented an opposite pattern with an increase in total lipids and glycogen at 25 °C. Serum cortisol and ammonium increased at the higher temperature suggesting an increased metabolism. In the brain, high temperatures had a marked effect on monoamine neurotransmitters, with increased levels of serotonin (5-HT) and norepinephrine (NAd). Fatty acids in white muscle were modulated by high temperatures. In general, saturated fatty acids were significantly decreased at higher temperatures, while for monounsaturated fatty acids only C20:1n9 showed a decrease at 25 °C. The most abundant polyunsaturated fatty acids in white muscle were C22:6n3 (DHA) and C20:5n3 (EPA), which did not change at a higher temperature, while C20:4n6 (ARA) and C18:3n3 (ALA) showed an increase and a decrease at 25 °C, respectively. In conclusion, we suggest that E. maclovinus juveniles tolerate up to 20 °C, increasing their metabolism without negatively affecting their physiology, while a temperature of 25 °C or higher could be lethal in a long-term scenario.