Abstract
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 with9.1±0.01 gwere 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.
Highlights
The intestine, as the complex multifunctional organ, that is, assumes great importance in the overall performance of fish [1]
In gilthead seabream, differences in intestinal histomorphology and microbiota diversity were not observed in fish fed different dietary P/CH ratios, differences were reported in digestive enzymes activity and oxidativerelated parameters [8–12]
Feed intake was increased in fish fed the P40/CH20 diet and 2 or 3 meals per day, while fish fed 1 meal per day presented higher protein efficiency ratio (PER), feed efficiency (FE), and nitrogen retention (NR), but lower final fish weight than the other groups
Summary
The intestine, as the complex multifunctional organ, that is, assumes great importance in the overall performance of fish [1]. It was already established that one of the most important factors to maintain intestinal health is the use of balanced diets which fulfil the basic nutritional species requirements [2]. Carnivorous fish, such as gilthead seabream (Sparus aurata), evolved to digest highly digestible and nutritionally dense diets, rich in proteins (P) and low in carbohydrates (CH) [1]. In gilthead seabream, differences in intestinal histomorphology and microbiota diversity were not observed in fish fed different dietary P/CH ratios, differences were reported in digestive enzymes activity and oxidativerelated parameters [8–12]. The current study aimed to evaluate the effects of FF (1, 2, or 3 meals per day) and dietary P/ CH ratio (P50/CH10 or P40/CH20) on gilthead seabream intestinal histomorphology, microbiota diversity, and digestive and oxidative stress status
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