Effects of Feeding Frequency and Dietary Protein/Carbohydrate Ratios on Gilthead Seabream (Sparus aurata) Intestinal Functionality and Health

The present study evaluated the effects of feeding frequency (FF) and dietary protein/carbohydrate (P/CH) ratios on intestinal histomorphology, microbiota profile, and digestive and oxidative stress-related enzyme activities of gilthead seabream (Sparus aurata). To this purpose, two practical diets were formulated: one with 50% P and 10% CH (P50/CH10) and other with 40% P and 20% CH (P40/CH20). Triplicate groups of fish with 9.1 & PLUSMN;0.01 g were fed these diets for 60 days until visual satiation at a FF of 1, 2, or 3 meals per day. Distal intestine histomorphology was not affected by diet composition or FF. However, the pyloric caeca (PC) of fish fed 1 meal per day presented more gut fold height alterations than the other groups, except in fish fed diet P50/CH10 3 meals per day, where no changes was observed. Fish fed diet P40/CH20 3 meals per day also presented higher PC submucosa cellularity than the other groups. Fish fed diet P40/CH20 presented a higher number of operational taxonomic units, microbial richness, and diversity indices than fish fed diet P50/CH10. Amylase was the only measured digestive enzyme affected by the experimental conditions, presenting higher activity in fish fed diet P50/CH10 once per day. Glucose-6-phosphate dehydrogenase activity was lower in fish fed 2 meals per day than only 1. While catalase activity was lower in fish fed 2 than 3 meals per day. Glutathione reductase activity was the only measured parameter affected both by dietary P/CH ratio and FF, being inferior in fish fed once per day the P50/CH10 diet than the P40/CH20 diet and, also in the P50/CH10 diet, to fish fed 1 than those fed 3 meals per day. Overall, no major interactions was observed between dietary P/CH ratio and FF; however, a P40/CH20 diet fed 2 meals per day might be recommended for gilthead seabream juveniles.