Digestive and metabolic consequences of on-growing greater amberjack (Seriola dumerili) juveniles at different temperatures. In-vivo and ex-vivo assessment

Aiming to elucidate the effects of temperature on different aspects of the fish digestive physiology that may affect the growth, we examined, firstly, variations in growth performance, feed intake, digestive enzyme activities, expression of transport related genes, metabolites in plasma and liver, and oxidative stress response in juveniles of greater amberjack ( Seriola dumerili ) growing during two months at 18, 22 and 26 °C of water temperature. Secondly, we analysed the epithelial function of the intestinal mucosa by electrophysiological ex-vivo experiments. As expected, body growth increased with increasing temperature in the tested range. Highest relative feed intake was observed at 26 °C, but the food conversion ratio was the same at 22 and 26 °C and less favourable at 18 °C. Digestive proteases activities were similar at 22 and 26 °C, while an evident effect of temperature was observed on lipids digestive capacity, being lipase activity undetectable at 18 °C. Electrophysiological assays revealed a relationship between temperature and intestinal mucosa plasticity. Temperature increase promoted epithelial functionality through higher tissue resistance and short-circuit current in mid-intestine at 26 °C, as well as better electrogenic amino acids transport. On the other hand, mRNA expression of peptide transporters tended to be higher in fish that grew at 18 °C, probably to reinforce the transport capacity. Plasma circulating levels of metabolites demonstrated higher energy and protein mobilization with the increasing temperature, where a hypometabolic state was denoted by lower cortisol levels at 18 °C together with an apparent switch from lipids to carbohydrate usage as energy source and increased oxidative stress in the liver at the lowest temperature. Altogether indicates that the tested temperatures are within the tolerance range for the species, although 22 and 26 °C appear as optimal temperatures for on-growing greater amberjack juveniles. Changes in nutrient digestion and absorption induced by temperature are related with both hydrolytic activity and remodelling of the intestinal mucosa. Impairing growth capacity and initial evidences of welfare compromise were observed at 18 °C. • Water temperature affected mainly the hydrolysis of lipids and in lesser extent to hydrolysis of proteins in the gut of greater amberjack. • Water temperature affected the integrity and transport capacity of the intestinal mucosa in greater amberjack. • At 26 °C fish are using primarily triacylglycerides for covering the energetic demand, while at 18 °C switched to carbohydrates. • A temperature range from 22 to 26 °C appears to be optimal for ongrowing greater amberjack juveniles, while evidences of welfare risk were observed at 18 °C.