Abstract
A 121-day feeding trial was undertaken to test the effects of two dietary lipid levels (16 and 21% L16, L21) in triplicated gilthead sea bream groups (initial weight: 67.5 g) reared at two different water temperatures (high, H 23°C and low, L 17°C) in the same recirculation system but exposed to a switch in temperature after 58 days. Fish kept at H were transferred to L (HL transition, autumn shift), and the fish kept at L were exposed to H (LH transition, summer shift), while continuing to receive the same diet to apparent satiation in each group. At the end of the trial, no significant diet effect on specific growth rate (SGR), feed intake (FI), and feed conversion rate (FCR) were detected in fish exposed to HL transition compared with those exposed to LH transition, while gross lipid efficiency (GLE) and lipid efficiency ratio (LER) were higher in L16. After temperature changes, L16 displayed higher SGR, FI, GLE, and LER, while mesenteric fat index was reduced. After temperature changes, the combined effects of low lipid diet and low temperature conditions resulted in higher pepsin activity, while trypsin, chymotrypsin, and lipase activities were generally higher at high lipid content. The combined effect of diet and temperature did not alter the metabolic plasma profile, except for the observed final higher aspartate aminotransferase (AST) and alkaline phosphatase (ALP) values when combining high dietary lipid (L21) and temperature changes. Different diets showed a significantly different gut microbiome layout, only at high temperature with L16 diet resulting in a higher load of Lactobacillus. On the contrary, no dietary impact on ecosystem diversity was observed, independently from the temperature. In addition, L16 diet in the HL transition favored an increase in Weissella and Bradyrhizobium genera in the gut microbiome, while in the final condition of LH transition, L21 diet favored a significant increase in Streptococcus and Bacillus. According to the results, the utilization of 16% dietary lipid levels in gilthead sea bream should be preferred during seasonal temperature changes in order to optimize feed utilization and gut health.
Highlights
Today, feeding strategy optimization related to environmental conditions is extremely necessary to pursue more intensive and more efficient aquaculture production in the Mediterranean basin
Though many studies have been conducted on the effect of water temperature on growth, physiological responses, and health in gilthead sea bream, so far, very few have investigated the possible interaction between temperature switch simulating seasonal variation and dietary lipid level, and no work exists on its capability to affect gut microbiota
Low dietary lipid improved feed intake, growth, and nutrient utilization after temperature changes, especially in fish entering optimal temperature (23◦C), which simulated the spring to summer water temperature switch
Summary
Today, feeding strategy optimization related to environmental conditions is extremely necessary to pursue more intensive and more efficient aquaculture production in the Mediterranean basin. Several studies have been devoted to developing winter feeds for overcoming metabolic alterations, immune suppression, and nutritional disorders (Silva et al, 2014; Richard et al, 2016; Schrama et al, 2017). While most of these diets were formulated in order to test the effectiveness of functional ingredients such as immunostimulants and antioxidants, their lipid content ranged from 17 to 19.7%. Especially at temperatures below 13◦C, if there is an excess in dietary lipid, it can be accumulated as a fat depot in perivisceral tissue due to low metabolic activity (Ibarz et al, 2007, 2010)
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