Effects of different levels of vegetable meal inclusion in replacement for fish meal in practical diets for sea bass (D. labrax) on gut histology and nutrigenomic activity.

The inclusion of plant-protein sources in aquafeed has increased due to the limited amount and increasing cost of fishmeal available for production of animal feeds (Burr et al., 2012). One of the greatest challenges for the aquafeed industry is to reduce fishmeal levels in feed further and increase the amount of plant protein and ingredient diversity in diets of carnivorous fishes. Fish meal free diets have been successfully used but problems related to some anti-nutritional factors have not allowed so far a total substitution of fish meal. In addition, higher inclusion level of vegetable meals, cause reduces weight gain and feed efficiency as well as morphological changes of the digestal intestinal epithelium (Buttle et al., 2004). Although several studies have reported change in growth performance and gut morphology in fish in response to vegetable meals inclusion, few have investigated gene expression and underlying mechanism (Murray et al., 2011). In this work we would like to study the mechanism that affect the utilization of pant products in aquafeed, focusing on the modulation in intestinal nutrient absorption capacity, their assimilation processes during the feeding time and the nutrigenomic effect of the vegetable sources. Four extrusion feeds with different level of fish meal (35%, 25%, 25% + Hemoglobin source, and 15% fish meal) were tested in a commercial fish farm for evaluate the effects of replacing fish meal with vegetable products. This trial was made in sea bass (D. labrax, 30g weight) that represents an important species for the European aquaculture. After the experimental time (14 weeks), the FCR ranged between 0.79 and 0.96 in fish fed with 35% and 15% fish meal inclusion feed, respectively. At the end of the trial, preliminary studies on oligopeptide transporter PepT1 mRNA levels in proximal and medium intestine, revealed significant differences in its expression in fish fed with higher fish meal percentage (1.32x106±5.70x105 n°mol/100ng RNA) respect to lower fish meal inclusion (1.07x106±1.16x106 n°mol/100ng RNA). After this preliminary results we are focusing our attention on the tissue expression as well as the regional distribution of the active transporter as well as metabolic enzyme at the mRNA level in the digestive tract, and relate these expression levels to different feed type. In addition we will report data from a study of the morphology of intestine to determine the effect of different diets on its histological appearance. A new experimental trial in commercial fish farm is still ongoing and will better explain the effect to the substitution level of vegetal raw material to replace fish meal in aquaculture commercial feed. Results from the histological analysis on intestinal tract will be also an important indicator of the nutritional welfare of the fish and their capability to assimilation processes. Finally, the levels of digestive enzyme, peptide transporter and their localization in the intestinal tract, will provide important information about their expression in response to a modified luminal nutrient availability.