This study evaluated the use of Ulva ohnoi as an ingredient in feeds for aquaculture in three different experiments. Experiment 1 was oriented to confirm the negative effect of U. ohnoi on fish digestion. Experiment 2 assessed the effect on growth, feed efficiency, and immune status of juvenile sea bass (Dicentrarchus labrax) fed on diets including U. ohnoi, previously treated or not with carbohydrases used to partially hydrolyze indigestible polysaccharides. Experiment 3 was aimed to evaluate the potential protective effect of U. ohnoi on the oxidative status of sea bream (Sparus aurata) challenged by the consumption of a feed formulated with the oil fraction completely oxidized. Results show a negligible effect of U. ohnoi meal on protein digestion when included in feeds at levels of 10% or less. Moreover, results of growth and feed use evidenced the possibility of using up to 5% inclusion of algal meal in feeds without adverse effects on the zootechnical parameters, while the enzyme pretreatment was ineffective to improve its nutritional use. Finally, the inclusion of U. onhoi in feeds determined both an immunostimulatory effect, evidenced by an increase in skin mucus lysozyme in the two mentioned fish species, and a positive influence on the oxidative metabolism of seabream when fed on a diet including rancid oil.

The Mugilidae are a group of fish with a great interest for aquaculture due to their omnivorous profile, rapid growth, and resistance to environmental variations. The selection of feed ingredients for these species is currently focused on an extensive use of plant by-products, with this being limited by their content in anti-nutritive factors (mainly phytate and non-starch polysaccharides; NSPs). Nevertheless, specific enzymes can be used to counteract some of those negative effects. In the present study, the effect of pretreating two high-plant feeds with a mixture of enzymes (glucanases + phytase) on the digestive use of protein and phosphorus by juvenile mullets (Mugil cephalus) was assessed using both in vitro and in vivo assays. The enzymatic treatment significantly modified the potential bioavailability of some nutrients, such as a reduction of sugars, pentoses, and phytic phosphorus. Also, it increased the digestibility of protein in one of the feeds but reduced that of phosphorus in both of them. The potential usefulness of enzyme treatment and the information provided by the two types of assays are discussed.

The possibility of improving the nutritional quality of plant byproducts (brewers’ spent grain and rice bran) through an enzyme treatment was tested in a formulated feed for grey mullet (Mugil cephalus). The enzyme treatment was carried out by Solid-State Hydrolysis (SSH) using a commercial preparation including carbohydrases and phytase. A feed prepared without the treatment and a commercial feed for carp were used as controls. In a preliminary short-term trial carried out at laboratory facilities, fish receiving the enzyme-treated feed showed significant improvement in both FCR and SGR when compared to those obtained with the untreated diet, although both experimental diets presented worse values than those obtained with the commercial feed. Different metabolic indicators including higher values of muscle glycogen and plasmatic triglycerides supported the positive effect of the enzyme treatment on the nutritional condition of the fish over those fed on the diet containing non-treated ingredients. Results of growth and feed efficiency that were obtained in a second long-term trial developed for 148 days under real production conditions evidenced the equivalence among the experimental and commercial diets and confirmed that enzyme pretreatment of plant ingredients by SSH may be a useful procedure to improve the nutritive value of high fiber plant byproducts when included in practical diets for this species and others with similar nutritional features.

The use of intensive systems in aquaculture causes an increase in environmental stress agents, reducing water quality and facilitating the appearance of pathologies in individuals. In this context, the selection of ingredients is a key strategy in managing the quality of aquafeed and the cultivation of aquaculture species. Considering this, wine by-products can be a potential functional ingredient due to several particular characteristics, such as their low cost, large volumes produced, and for being a natural source of bioactive compounds with antioxidant activity. The present study developed different experiments focused on evaluating the benefits of feeding juvenile European sea bass during 5 weeks with feeds incorporating 0.4% red wine grape pomace (GP). At the end of the feeding period, potential modifications in metabolism, immunological and oxidative status, and functionality of intestinal microbiota were assessed as well as the potential protective effect against oxidation in fish fillets during 6 days of cold storage (4 °C). In addition, the preservative effect of GP on the feed when stored for a period of 12 weeks at two different temperatures (4 °C and 25 °C) was evaluated. The results demonstrated that the inclusion of GP in feeds for European sea bass prevents oxidation when stored at room temperature. In addition, a general improvement in the physiological and immunological status, as well as fillet quality, was evidenced.

Increasing attention is currently being paid to the protective role of polyphenols in health and oxidative status in fish. For this reason, the potential use of different natural sources of such compounds, like wine by products, is under study. One key step required to gain a better understanding on the biological roles of polyphenols for a given species is to assess the different factors affecting their digestive bioaccessibility, and a great number of such studies is based in the use of in vitro digestion models. In the present study the potential digestive bioavailability of the phenolic compounds present in wine bagasse and lees was evaluated for two fish species showing great differences in their digestive phisyiology: the omnivorous gilthead sea bream (Sparus aurata) and the herbivorous flathead grey mullet (Mugil cephalus). The study was developed using in vitro models adapted to simulate their digestion and a factorial experimental design that simultaneously evaluated the effects of the ingredient used as source of polyphenols, presence or absence of feed matrix, fish species and digestion time. The release of the phenolic compounds was evaluated using ultra-high performance liquid chromatography (UHPLC) coupled to high resolution mass spectrometry (HRMS) detection. Both the presence of feed matrix and the type of wine by-product showed a significant effect on the digestive release of both total and specific types of polyphenols while fish species showed to be significant only for some specific compounds, like eriodyctiol or syringic acid. The time of digestion was not identified as a statistically significant factor in the release of phenolic compounds due to the great variability in the patterns observed that were classified as early, sustained and late. The observed great variations in the patterns of release of different types of phenolic compounds with time suggest an important effect of gut transit rates on the net bioavailability of a given phenolic compound in the live fish. The present study is, to our knowledge, the first one on which an in vitro approach was applied to assess to what extent the possible complexation of wine polyphenols present in wine by-products with either digestive enzymes or components of the feed matrix could limit their bioaccessibility if included in diets of two different fish species.

Brewer’s spent grain (BSG), the primary byproduct generated by the brewing industry, holds significant potential as an ingredient in aquafeeds. However, its high content of non-starch polysaccharides (NSP) restricts the amount that can be incorporated into fish diets. To address these limitations, various pretreatment methods (physical, chemical, or enzymatic) can be applied prior to its inclusion in feed formulations. The objectives of the present study were (i) to optimize the conditions for enzymatic or microwave pretreatments to enhance the nutritional and functional profile of BSG, (ii) to determine the bioaccessibility and availability of specific nutrients and antioxidant compounds in diets including a high amount of BSG (pretreated or not) using an in vitro assay simulating the digestion of the gilthead seabream (Sparus aurata), and (iii) to evaluate the effect of such diet pretreatments on growth, metabolism, intestinal microbiota, and oxidative status in live fish. For this study, three experimental diets were formulated: one containing 20% untreated BSG (C) and two containing the same amount of BSG pretreated either enzymatically (H) or with microwave heating (MW). Each diet was administered ad libitum to triplicate groups of 22 juvenile sea bream (mean weight 60 g) over a period of three months. The results indicated that the microwave-treated BSG led to improved growth (0.69 ± 0.02%) and feed efficiency (0.80 ± 0.02 weight gain/total feed intake) and enhanced immune status (alkaline phosphatase activity = 11,811.68 ± 3426.92 U/mg SP), compared to the control diet (SGR = 0.59 ± 0.06%; FE: 0.68 ± 0.03 weight gain/total feed intake; alkaline phosphatase activity = 8590.29 ± 3663.44 U/mg SP). Moreover, fish fed on both pretreated BSG diets exhibited significant differences in metabolic parameters and functional profile of their intestinal microbiota when compared to the control group. Consequently, the findings suggest that the pretreatment of BSG, whether by enzymatic or microwave methods, results in notable differences in its nutritional value and the bioavailability of functional components, which, in turn, have a substantial impact on the growth and metabolism of gilthead seabream.