Modulation of digestive and absorptive processes with age and/or after a dietary change in gilthead sea bream

• Fish growth down-regulated digestive enzyme and nutrient absorption capacities.
• Digestive and absorptive compensatory mechanisms were higher in VO fish than in FO.
• Digestive adaptation to a diet lipid change is slower in small fish than in large.
• No effects by long term dietary treatment were found in SGR.

During a 19-week trial, sea bream juveniles were fed with two isonitrogenous and isoenergetic diets in which 75% of the fish meal was replaced by plant protein sources and that only differed in the lipid source: fish oil (FO) or vegetable oil (VO). After the growth period, intestinal pH content, digestive enzyme activities, nutrient absorption capacity and final weight were studied in the pre-feeding stage on the FO or VO diet and also after a dietary change at different animal weights (92 g, 147 g, 233 g), both in the short term and at the end of the trial.Intestinal pH content, alkaline protease, α-amylase and lipase activities and nutrient absorption capacities decreased as the animals grew. Moreover, the VO group tended to have higher alkaline protease and α-amylase activities, whereas lipase activity was higher in the FO group; these changes were significant in small fish. The absorption capacities of essential amino acids were higher than those of non-essential amino acids and d-Glc. Moreover, absorption capacities were higher in small VO animals compared to FO. No changes in growth rate were found at the end of the trial. However, FO animals had a higher growth rate during the first half of the trial after which growth slowed, whereas VO animals grew at a lower but more steady rate throughout the trial.Small animals were not able to adapt their digestive enzyme activities or nutrient absorption capacities to the new or original feeding condition after a short-term dietary change, whereas large animals generally adapted.After 9–15 weeks on the FO diet, animals were able to adapt their protease activity and absorption capacity to the new situation; however, α-amylase activity declined. In contrast, after changing to the VO diet animals up-regulated their nutrient absorption capacities and α-amylase activity whereas alkaline protease activity tended to decrease. At the end of the trial final body weight was not affected by dietary treatment.Statement of relevance“Wash out” or FO diet feeding in early stages and VO later?