Diets For European Sea Bass Research Articles

Grape pomace in diets for European sea bass: influence on oxidative status, intestinal microbiota, and fillet quality

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.

Dietary Salicornia ramosissima improves the European seabass (Dicentrarchus labrax) inflammatory response against Photobacterium damselae piscicida.

Modern fish farming faces challenges in sourcing feed ingredients, most related with their prices, 21 availability, and specifically for plant protein sources, competition for the limited cultivation space for 22 vegetable crops. In that sense, halophytes have the added value of being rich in valuable bioactive compounds and salt tolerant. This study assessed the inclusion of non-food fractions of S. ramosissima in European seabass diets. Different levels (2.5%, 5%, and 10%) were incorporated into seabass diets, replacing wheat meal (diets ST2.5, ST5, and ST10) or without inclusion (CTRL). Experimental diets were administered to seabass juveniles (8.62 ± 0.63g) for 34 and 62 days and subsequent inflammatory responses to a heat-inactivated Photobacterium damselae subsp. piscicida (Phdp) were evaluated in a time-course manner (4, 24, 48, and 72h after the challenge). At each sampling point, seabass haematological profile, plasma immune parameters, and head-kidney immune-related gene expression were evaluated. After both feeding periods, most parameters remained unaltered by S. ramosissima inclusion; nonetheless, seabass fed ST10 showed an upregulation of macrophage colony-stimulating factor 1 receptor 1 (mcsf1r1) and cluster of differentiation 8 (cd8β) compared with those fed CTRL after 62 days of feeding. Regarding the inflammatory response, seabass fed ST10 showed lower plasma lysozyme levels than their counterparts fed ST2.5 and ST5 at 24h following injection, while 4h after the inflammatory stimulus, seabass fed ST10 presented higher numbers of peritoneal leucocytes than fish fed CTRL. Moreover, at 4h, fish fed ST2.5, ST5, and ST10 showed a higher expression of interleukin 1β (il1β), while fish fed ST5 showed higher levels of ornithine decarboxylase (odc) than those fed CTRL. An upregulation of macrophage colony-stimulating factor 1 receptor 1 (mcsf1r1) and glutathione peroxidase (gpx) was also observed at 72h in fish fed ST10 or ST5 and ST10 compared with CTRL, respectively. In conclusion, incorporating up to 10% of the non-food fraction S. ramosissima in feed did not compromise seabass growth or immune status after 62 days, aligning with circular economy principles. However, S. ramosissima inclusion improved the leucocyte response and upregulated key immune-related genes in seabass challenged with an inactivated pathogen.

Replacement of fish oil by alternative n-3 LC-PUFA rich lipid sources in diets for European sea bass (Dicentrarchus labrax)

IntroductionIn order to ensure lipid quality of cultured fish and an environmentally sustainable production, new alternative sources of EPA and DHA are needed to replace traditional lipid sources, such as fish oil.MethodsDifferent combinations of alternative marine lipid sources rich in n-3 LC-PUFA available in the market were herein evaluated to replace traditional fish oil (sardine oil) in diets for European sea bass (Dicentrarchus labrax). A commercial-type diet (CTRL), containing 1.6% of EPA + DHA, 5% sardine oil and 8% rapeseed oil was used as a negative control. Another diet (SARDINE) formulated with 8.5% sardine oil, 4.5% rapeseed oil and 2.5% EPA + DHA was used as the positive control. Three experimental diets were formulated to completely replace sardine oil with alternative sources, targeting approximately the same EPA + DHA level as the positive control: the SALMON diet contained 9.9% salmon by-product oil mixed with 3.1% of an algal oil rich in EPA and DHA, while the ALGARAPE and the ALGASOY diets included 4.4% of the algal oil and 8.6% of either rapeseed or soybean oil, respectively. A sixth diet (ALGABLEND) was formulated to partially replace sardine oil with salmon by-product oil and rapeseed oil, balanced with 2% of algae biomass. The experimental diets were hand-fed to 118 g fish for 54 days. ResultsAll diets were well-accepted by fish and no significant differences were found in feed efficiency, growth performance, somatic indexes or whole body composition among treatments. At the end of the trial, regardless the dietary EPA + DHA level, all fillets contained more than 250 mg of EPA + DHA per 100 g fresh weight, meeting EFSA recommendations for cardiovascular risk prevention for European adults (> 250 mg day -1). DiscussionOverall, this study demonstrated that combining expensive sources of n-3 LC PUFA (Veramaris® or Algaessence Feed™ with low-priced sustainable oils (salmon by-products oil or vegetable oils) allows fortifying European sea bass flesh with EPA and DHA, without major textural changes. This approach is a successful strategy for mitigating the negative effects associated with the high inclusion of vegetable oils. However, the retention of n-3 LC-PUFA in muscle was not significantly increased, suggesting that there is a maximum dietary threshold beyond which β-oxidation might be promoted, and hence there is no advantage in increasing the dietary level of these fatty acids in European sea bass diets.

Towards sustainable aquaculture: Assessing polychaete meal (Alitta virens) as an effective fishmeal alternative in European seabass (Dicentrarchus labrax) diets

In recent years, the pursuit of sustainable aquaculture practices has focused on alternatives to fisheries-derived ingredients, to avoid economic and environmental unsustainability. Low-trophic organisms, such as polychaetes, could be a suitable alternative to fishmeal due to their high protein content. This study aimed to investigate the feasibility of replacing fishmeal with the polychaete meal (Alitta virens; PM) in diets for European seabass (Dicentrarchus labrax; Wi, ∼14.5 g). Four isoproteic (51% dry matter, DM) and isolipidic (17% DM) diets were fed to seabass juveniles: a fishmeal-based diet (FM) and three experimental diets with PM at inclusion levels of 2.5% (PM2.5), 5% (PM5), and 10% (PM10), replacing 10%, 20% and 40% of fishmeal, respectively. After 93 days of feeding, the effects of the PM on growth, digestibility, nutrient utilization, plasma metabolites, liver lipogenic activity, and anterior intestine histomorphology were analyzed. The environmental impact of all diets was also assessed. All diets were well-accepted by the fish, and promoted equal growth performance, ensuring high feed efficiency. The muscle EPA + DHA content in all dietary groups exceeded the recommended levels for human consumption. Hepatic lipogenesis and plasma triglyceride and non-esterified fatty acids (NEFA) levels were increased in fish fed PM2.5, suggesting that the PM promoted alterations in lipid metabolism, especially at low inclusion levels. PM2.5 also seemed to enhance the absorption capacity of the anterior intestine by increasing villus length and goblet cells number/area, albeit without impacting nutrient digestibility and growth performance. Furthermore, copper digestibility increased with higher levels of PM inclusion. The assessment of environmental sustainability indicated that the experimental diets incorporating PM present a more sustainable option compared to fishmeal. Overall, this study demonstrated that PM can serve as a sustainable alternative to fishmeal, replacing it by up to 40%, without compromising European seabass growth and nutrient utilization, while guaranteeing a high nutritional quality fillet for human consumption. The best environmental performance could be achieved with a diet comprising 5% to 10% (w/w) PM content. However, further research is needed to understand the underlying mechanisms of PM's effects on intermediary metabolism and its potential as a functional ingredient.

Novel chitinolytic Bacillus spp. increase feed efficiency, feed digestibility, and survivability to Vibrio anguillarum in European seabass fed with diets containing Hermetia illucens larvae meal

Insect meals (IM) are being pointed out as a promising sustainable protein source. However, chitin in IM may negatively interfere with fish performance and nutrient availability. Given that carnivorous fish have a low or inexistent ability to digest chitin, novel strategies are needed to overcome chitin-imposed bottlenecks. Carbohydrolytic sporeforming probiotics offer a competitive industrial approach, being able to resist the harsh feed manufacturing process, transport, storage, and animal's gastrointestinal tract, while being able to increase the digestibility of otherwise indigestible components. Aiming to increase IM chitin digestibility, two chitinolytic sporeforming fish isolates (Fish isolates 645 (FI645) and 658 (FI658)), closely related to Bacillus licheniformis, were isolated from European sea bass (ESB) gastrointestinal tract, and incorporated (individually or as a mixture) in ESB diets with high defatted Hermetia illucens larvae meal (HM) levels (30% inclusion). FI were evaluated regarding their effects on ESB growth performance and digestibility. The spores were able to maintain their viability throughout the 180 days of diet storage at room temperature. Dietary inclusion of FI645 led to higher chitin digestibility. Concomitantly, the digestibility of dry matter, protein, and energy increased, overall leading to higher feed efficiency and protein efficiency ratio. Dietary inclusion of FI645 led to increased plasma N-acetylglucosamine (GlcNAc) levels. This is the first evidence for diet-mediated modulation of plasma GlcNAc concentrations. Dietary inclusion of FI645 also increased the expressions of the genes coding for N-acetylglucosamine kinase (nagk) and GlcNAc phosphomutase (pgm3), key enzymes from the GlcNAc salvage pathway and the hexosamine biosynthetic pathway (HBP). On the other hand, no differences were found for the expression of N-acetyl-D-glucosamine-6-phosphate deacetylase (amdhd2), a precursor enzyme for GlcNAc redirection to glycolysis. These results hint that free GlcNAc resulting from increased chitin digestibility might be preferentially redirected to protein O-GlcNAcylation processes through HBP in fish cells. Additionally, when challenged with Vibrio anguillarum, and after being feed for one month with the same diets, D645 also increased ESB survival from 52.5% to 77.5%, when compared to the control. Together, these results establish the potential of using FI645 as a probiotic for enhancing chitin digestion and acting as a prophylactic agent for ESB protection against V. anguillarum infection. This strategy opens novel possibilities for using commodities, including high chitin levels in aquafeeds, and reducing the use of antibiotics in aquaculture.

Solid-State Fermentation as Green Technology to Improve the Use of Plant Feedstuffs as Ingredients in Diets for European Sea Bass (Dicentrarchus labrax) Juveniles.

This study aimed to evaluate the utilization by juvenile European sea bass of a SSFed PF mixture with Aspergillus niger CECT 2088. A 22-day digestibility and a 50-day growth trial were performed testing four diets, including 20 or 40% of an unfermented or SSFed PF mixture (rapeseed, soybean, rice bran, and sunflower seed meals, 25% each). SSF of the PF added cellulase and β-glucosidase activity to the diets. Mycotoxin contamination was not detected in any of the experimental diets except for residual levels of zearalenone and deoxynivalenol (100 and 600 times lower than that established by the European Commission Recommendation-2006/576/EC). In diets including 20% PF, SSF did not affect growth but increased apparent digestibility coefficients of protein and energy, feed efficiency, and protein efficiency ratio. On the contrary, in diets including 40% PF, SSF decreased growth performance, feed intake, feed and protein efficiency, and diet digestibility. SSF decreased the intestinal amylase activity in the 40% SSFed diet, while total alkaline proteases decreased in the 20% and 40% SSFed diets. Hepatic amino acid catabolic enzyme activity was not modulated by SSF, and plasma total protein, cholesterol, and triglyceride levels were similar among dietary treatments. In conclusion, dietary inclusion of moderate levels of the SSFed PF, up to 20%, improves the overall feed utilization efficiency without negatively impacting European sea bass growth performance. The replacement of PF with the SSFed PF mixture may contribute to reducing the environmental footprint of aquaculture production.

Fishmeal, plant protein, and fish oil substitution with single-cell ingredients in organic feeds for European sea bass (Dicentrarchus labrax).

Single-cell ingredients (SCI) are considered promising nutrient sources which are produced using environmentally friendly biotechnological processes. The aim of the current study was to evaluate the replacement of fishmeal, plant protein sources, and fish oil with SCI in organic feeds for European sea bass (Dicentrarchus labrax). Bacterial protein, yeast protein, and microalgae were used to replace fishmeal trimmings, soya bean meal, and fish oil from trimmings. Triplicate groups (30 fish per replicate) of European sea bass (14.4 ± 2.4g) were fed the experimental diets for 71days. The results showed that the incorporation of SCI at all levels of inclusion significantly enhanced nutrient digestibility. Additionally, growth performance parameters were not affected by SCI inclusion, exhibiting similar or improved values. Moreover, a tendency for improved anterior and posterior gut structure was observed and a significant increase of lysozyme activity at the two highest inclusion levels of SCI was determined. Overall, the results showed that the inclusion of SCI at 15% (bacterial: yeast: algae-9.4: 4.7: 1) is possible without compromising any of the parameters evaluated. According to these findings, a higher substitution of fishmeal trimmings, plant protein sources, and fish oil from trimmings with SCI in organic diets for European sea bass (D. labrax) can be further evaluated in future studies.

Effect of Feeding Acid Oils on European Seabass Fillet Lipid Composition, Oxidative Stability, Color, and Sensory Acceptance.

Acid oils (AO) are fat by-products of edible oil refining with a high energetic value, being an interesting option for a more sustainable aquaculture nutrition. This study was conducted to evaluate the effects of the partial replacement of fish oil (FO) in diets by two AO instead of crude vegetable oils on the lipid composition, lipid oxidation and quality of fresh European seabass fillets, and after their commercial refrigerated storage for 6 days. Fish were fed with five different diets, the added fat being FO (100%) or a blend of FO (25%) and another fat (75%): crude soybean oil (SO), soybean-sunflower acid oil (SAO), crude olive pomace oil (OPO), or olive pomace acid oil (OPAO). Fresh and refrigerated fillets were assessed for fatty acid profile, tocopherol (T) and tocotrienol (T3) composition, lipid oxidative stability, 2-thiobarbituric acid (TBA) value, volatile compound content, color, and sensory acceptance. Refrigerated storage did not affect T + T3 total content but increased secondary oxidation products (TBA values and volatile compound contents) in fillets from all diets. The FO substitution decreased EPA and DHA and increased T and T3 in fish fillets, but the recommended human daily intake of EPA plus DHA could still be covered with 100 g of fish fillets. Both a higher oxidative stability and a lower TBA value were found in SO, SAO, OPO, or OPAO fillets, obtaining the greatest oxidative stability in OPO and OPAO fillets. Sensory acceptance was not affected by the diet or the refrigerated storage, while the differences found in color parameters would not be perceived by the human eye. According to the oxidative stability and acceptability of flesh, SAO and OPAO are adequate replacements of FO as energy source in European seabass diets, which implies that these by-products can be upcycled, improving the environmental and economical sustainability of aquaculture production.

Total fishmeal replacement by defatted Tenebrio molitor larvae meal induces alterations in intermediary metabolism of European sea bass (Dicentrarchus labrax).

The replacement of fishmeal (FM) by insect meal (IM) in aquafeed formulation has been thoroughly studied lately, but little is known about their impact on nutrient metabolism of fish. This study evaluated the impact not only of partial but also total FM replacement by IM on intermediary metabolism of European sea bass (Dicentrarchus labrax). A fishmeal-based diet was used as a control (CTRL) and two other diets were formulated to include 20% and 40% of defatted Tenebrio molitor larvae meal (dTM), replacing 50% (TM50) and 100% (TM100) of fishmeal (FM), respectively. After a 16-week feeding trial, a multidisciplinary approach including assessment of histological, biochemical, molecular, and enzymatic parameters was adopted to investigate hepatic and plasmatic responses to the different dietary formulations. The results obtained demonstrated that dTM can be successfully used to replace 50% of FM in diets for European sea bass, without adversely affecting liver health or intermediary metabolism of nutrients. As for TM100, although no signs of steatosis were observed in the liver, the activity of glycolytic and lipogenic genes and enzymes increased when compared to CTRL diet (P < 0.05), resulting in higher levels of plasmatic non-esterified fatty acids and triacylglycerides (P < 0.05), which in the long-term may compromise fish health, thus precluding such a high degree of substitution for use in practical diets for European sea bass.

Gill Oxidative Stress Protection through the Use of Phytogenics and Galactomannan Oligosaccharides as Functional Additives in Practical Diets for European Sea Bass (Dicentrarchus labrax) Juveniles.

The aim of the present study is to evaluate the potential of two functional additives as gill endogenous antioxidant capacity boosters in European sea-bass juveniles fed low-FM/FO diets when challenged against physical and biological stressors. For that purpose, two isoenergetic and isonitrogenous diets with low FM (10%) and FO (6%) contents were supplemented with 5000 ppm plant-derived galactomannan-oligosaccharides (GMOS) or 200 ppm of a mixture of garlic and labiate plant essential oils (PHYTO). A control diet was void from supplementation. Fish were fed the experimental diet for nine weeks and subjected to a confinement stress challenge (C challenge) or a confinement stress challenge combined with an exposure to the pathogen Vibrio anguillarum (CI challenge). Both GMOS and PHYTO diets attenuated fish stress response, inducing lower circulating plasma cortisol and down-regulating nfκβ2 and gr relative gene-expression levels in the gill. This attenuated stress response was associated with a minor energetic metabolism response in relation to the down-regulation of nd5 and coxi gene expression.

Growth, plasma biochemistry and immune-related gene expression of European sea bass (Dicentrarchus labrax) fed bioactive peptides from farmed salmon by-products

The effect of bioactive peptides (BPs) derived from farmed Atlantic salmon (Salmo salar) by-products on growth, blood biochemistry and immune response was tested in European sea bass (Dicentrarchus labrax). Three diets with different levels of BPs (0% BP0, 5% BP5, 10% BP10) in substitution for fish meal (FM) were administered to triplicate fish groups over 58 days. At the end of the trial, fish were subjected to suboptimal environmental conditions (high water temperature, low oxygen) for 7 days. No significant differences (p > 0.05) were observed in final body weight, specific growth rate, feed intake, and feed conversion while lipid efficiency was higher (p < 0.05) in BP10. At the end of the growth trial, plasma profile remarked previous studies on this species; however cholesterol was higher in BP5 while glucose decreased with increasing BP content. In addition, a reduction in plasma total protein, cholesterol, high-density lipoprotein and triglycerides after environmental stressful conditions was observed only in BP5 supporting a better lipid utilization for energy purposes as a strategy to counteract high energy demand periods. The immune gene analysis showed in BP5 a reduction of the pro-inflammatory interleukin 1β (IL-1β), IL-8, and a significant increase in the expression of the anti-inflammatory interleukin-10; on the contrary, BP10 led to an increase in the expression of IL-1β, and IL-8. In conclusion, data suggest that BPs from salmon by-products have a promising implication as circular and functional ingredients for European sea bass diets. In addition to being a valid alternative ingredient to fishmeal in terms of acceptability and growth, it could enhance physiological mechanisms related to lipid metabolism and immune response.

Gracilaria gracilis and Nannochloropsis oceanica, singly or in combination, in diets alter the intestinal microbiota of European seabass (Dicentrarchus labrax)

Algae feeds and fish gut microbiota have been given importance in the past few years because of the necessity to rely on sustainable ingredients in aquafeeds and the link of host-associated microbes to organismal health. But little is known about the potential of algae, particularly of micro- and macroalgae combination, to shape the intestinal bacterial communities. Hence, in the present work, the 16S rRNA gene sequencing technique was employed to unravel the effects of the seaweed Gracilaria gracilis and the microalga Nannochloropsis oceanica - included either singly or in combination in the diets of European seabass - on the diversities and composition of the gut bacterial communities. Results indicated that 8% inclusion of either G. gracilis (GRA) or N. oceanica (NAN) led to a reduction in the gut microbial diversity. On the other hand, inclusion of the micro- and macroalga in a blend (NANGRA) mitigated these plausible effects on the intestinal bacterial communities. The core microbiota of European seabass was composed of both beneficial (Lactobacillus and Cetobacterium) and potentially pathogenic (Flavobacterium) bacteria. The GRA diet was associated with a lower abundance of carbohydrate degraders and also promoted the growth of bacteria capable of outcompeting fish pathogens (Sulfitobacter and Methylobacterium). On the other hand, the NAN diet led to a higher representation of the genus Bacillus, with probiotic potential, accompanied by a decrease in Vibrio, a genus encompassing several fish pathogenic species. These findings demonstrate the ability of micro- and macroalgae to modulate the gut microbiota of European seabass, with plausible implications to host gut homeostasis.

Innovative swine blood hydrolysates as promising ingredients for European seabass diets: Impact on growth performance and resistance to Tenacibaculum maritimum infection

Hydrolysates from high-protein coproducts are rich in bioactive peptides (small amino acid chains with properties beyond their nutritional value). When included in aquafeeds, they may promote fish robustness while increasing animal blood value and minimizing waste, contributing to a circular economy. This work assessed how innovatively produced blood hydrolysates (BH) included in plant-based diets for European seabass (Dicentrarchus labrax) affected growth performance and resistance to Tenacibaculum maritimum infection. Three fractions of swine BH obtained by autohydrolysis (AH) or enzymatically were selected. AH fraction was oven-dried, whilst the enzymatically obtained BH were further submitted to a micro (RMF) and nanofiltration (RNF) and the respective retentates freeze-dried. A commercially based diet was formulated, where 50% of fishmeal was replaced by vegetable proteins, and used as negative control (NC). Each BH fraction was then added at 3% to the NC and further compared to a fishmeal-based diet (positive control, PC); all diets remained isolipidic and isoproteic. Diets were assigned to triplicate groups of European seabass juveniles (12.3 ± 1.4 g) and fed three times daily until apparent satiation in a recirculating saltwater system. After a 12-week growth trial, fish were bath challenged with T. maritimum and cumulative mortality followed for 8 days. A digestibility trial was also performed in parallel. Hydrolysates-containing diets had a significantly lower apparent digestibility coefficient (ADC) of dry matter compared to the PC, but RNF did not differ from the NC. RMF and AH had lower lipid ADCs than both controls, while the RNF only differed from the PC. Mineral ADCs of PC, NC and RNF were similar. Calcium ADC in RMF and AH was significantly lower than all other diets; RMF also displayed lower copper and potassium ADCs. Fish fed PC had the highest final weight, followed by NC and RNF. Daily growth index and feed conversion ratio (FCR) of RNF was similar to both controls. RMF induced the lowest final weight, highest FCR and reduced villus length in anterior intestine. This diet has also resulted in increased plasmatic peroxidase, but lower lysozyme, compared to all other treatments, showing the lowest disease resistance. Results clearly show that the RNF was the only test diet that significantly reduced European seabass mortality after T. maritimum infection, without affecting fish growth in relation to a practical plant-protein based diet, highlighting its high potential for aquafeeds supplementation.

A plant-based diet supplemented with Hermetia illucens alone or in combination with poultry by-product meal: one step closer to sustainable aquafeeds for European seabass

BackgroundIncreasing demand for high-value fish species and pressure on forage fish is challenging aquaculture to ensure sustainable growth by replacing protein sources in aquafeeds with plant and terrestrial animal proteins, without compromising the economic value and quality of the final fish product. In the present study, the effects of a plant protein-based diet (CV), two plant-based diets in which graded amounts of plan protein mixtures were replaced with Hermetia illucens meal alone (VH10) or in combination with poultry by-product meal (PBM) (VH10P30), a fishmeal (FM) diet (CF) and an FM diet supplemented with H. illucens (FH10) on growth performance, gut health and homeostasis of farmed subadult European seabass were tested and compared.ResultsFish fed the VH10 and VH10P30 diets showed the highest specific growth rates and lowest feed conversion ratios among the tested groups. Expectedly, the best preservation of PI morphology was observed in fish fed the CF or FH10 diets, while fish fed the CV diet exhibited significant degenerative changes in the proximal and distal intestines. However, PBM supplementation mitigated these effects and significantly improved all gut morphometric parameters in the VH10P30 group. Partial substitution of the plant mixture with insect meal alone or PBM also induced most BBM genes and activated BBM enzymes, suggesting a beneficial effect on intestinal digestive/absorption functions. Regarding intestinal microbiota, fish fed diets containing H. illucens meal (FH10, VH10, VH10P30) had the highest richness of bacterial communities and abundance of beneficial genera such as Lactobacillus and Bacillus. On the other hand, fish fed CV had the highest microbial diversity but lost a significant component of fish intestinal microbiota, the phylum Bacteroidetes. Finally, skin pigmentation most similar to that of farmed or even wild seabass was also observed in the fish groups fed CF, FH10 or VH10P30.ConclusionPlant-based diets supplemented with PBM and H. illucens pupae meal have great potential as alternative diets for European seabass, without affecting growth performance, gut homeostasis, or overall fitness. This also highlights the importance of animal proteins in diets of European seabass, as the addition of a small amount of these alternative animal protein sources significantly improved all measured parameters.

Pre-treatment of Ulva rigida improves its nutritional value for European seabass (Dicentrarchus labrax) juveniles

Macroalgae are promising ingredients for aquafeeds, but their recalcitrant polysaccharide structure limits their wide use. To disrupt this structure, different physical (ultra-sounds, autoclave, microwaves), chemical (acid, alkaline), and biotechnological (solid-state fermentation, SSF; SSF followed by sequential hydrolysis, SSF-SH) treatments were carried out in Ulva rigida. The chemical composition, morphological microstructure, release of reducing sugars, soluble protein, and phenolic compounds were evaluated in the final products.All treatments increased U. rigida protein content, while lipid content increased after autoclave, ultra-sound, microwave, and SSF treatments. SSF-SH treatment was more effective in disrupting the cellulose and hemicellulose fractions, resulting in a higher reducing sugars release. The alkaline treatment was more efficient in reducing lignin content and increasing phenolic compounds, antioxidant activity, and soluble protein of U. rigida.The most promising products were then included at 5 % in diets for European seabass (Dicentrarchus labrax) juveniles. Crude, ultra-sound, alkaline, and SSF-SH-treated U. rigida reduced fish growth, while SSF-treated U. rigida resulted in similar growth as the positive control (fish meal-based diet). Feed intake was reduced in all experimental groups, but the feed efficiency of fish fed SSF-U. rigida diet and the protein efficiency ratio of fish fed crude, alkaline, and SSF-treated U. rigida were higher than the positive control. The highest total alkaline proteases activity was achieved with the crude U. rigida diet, while no differences were observed in fish fed the positive control, ultra-sound, and SSF diets.Overall, of the processing methods tested, the most efficient was SSF, which improved feed efficiency of European seabass juveniles fed U. rigida-including diet without affecting growth performance.

Understanding the interaction between terrestrial animal fat sources and dietary emulsifier supplementation on muscle fatty acid profile and textural properties of European sea bass

The main goal of this work was to compare the dietary inclusion of poultry fat with mammal fat, and to understand the possible beneficial effects of an emulsifier in commercial-based diets for European sea bass (Dicentrarchus labrax) tested under an industrial scale, without control of environmental conditions. Effects on growth performance and muscle quality in terms of fatty acid (FA) profile, textural properties and colour, were evaluated. For this purpose, four isoproteic (45%) and isolipidic (21%) diets were formulated using the same protein sources. The lipid fraction of the diets varied, and comprised 55% fish oil and either 45% poultry fat or mammal fat, with or without an emulsifier. A 12 weeks' growth trial was carried out with commercial-sized juveniles (255.7 ± 15.2 g) in an open-through aquaculture system. All diets were equally well-accepted by the fish, with no differences in terms of feed efficiency and growth. The inclusion of the emulsifier led to increased whole body lipids and energy contents, regardless of the type of fat. Fish fed with the mammal fat diet had a higher muscle lipid content, but lower n-6 PUFA, without changes in the n-3 PUFA and in the n-3/n-6 PUFA ratio. The dietary inclusion of mammal fat, contrarily to poultry fat, resulted in increased amounts of EPA and DHA in the muscle which were within the recommended levels for human consumption to decrease the risk of cardiovascular diseases (> 0.25 g 100 g−1). Fish fed mammal fat also demonstrated an increase of muscle instrumental lightness and hardness. These results indicate that terrestrial animal fats can be promising sources of lipids for aquafeeds, highlighting mammal fat as a viable by-product to include in European sea bass diets.

Assessing the Influence of Dietary Pediococcus acidilactici Probiotic Supplementation in the Feed of European Sea Bass (Dicentrarchus labrax L.) (Linnaeus, 1758) on Farm Water Quality, Growth, Feed Utilization, Survival Rate, Body Composition, Blood Biochemical Parameters, and Intestinal Histology

The probiotics are being used as ecofriendly and bioremediation tools for developing sustainability to aquaculture. The present study was conducted to explore the practical capability of using dietary lactic acid bacteria (Pediococcus acidilactici) probiotics and see how its dose variation affected the water quality, growth performance, survival rate, body composition, blood biochemical parameters, and intestinal histology of European sea bass (Dicentrarchus labrax L.). A total of 120 fingerlings with an initial weight of 9 ± 0.2 g were divided into four groups, each with three replicates. The feeding experiment lasted for 60 days. In addition to the control (without probiotics) (T0), fish were fed diets containing (T1) 2.0, (T2) 2.5, and (T3) 3.0 g of probiotics per kg of diet twice a day. When compared to the control, sea bass fed probiotic-supplemented diets had significantly higher growth parameters, fish body “crude lipid,” and villi height ( p &lt; 0.05 , p &lt; 0.01 , and p &lt; 0.001 ). The P. acidilactici probiotic treatments improved survival rate, feed conversion ratio, body composition, and blood biochemical markers, but not statistically significant ( p &gt; 0.05 ). Also, in regard to water quality, P. acidilactici drastically reduced ammonia and pH levels. In this experiment, fish fed with a dosage of 3.0 g of this commercial probiotic per kg of probiotics performed better. The study found that including probiotics in the diets of European sea bass improved growth, body composition, survival rate, blood biochemical markers, intestinal histology, and some water quality parameters.

Application of fermented brewer's spent grain extract in plant-based diets for European seabass juveniles

This work aimed to evaluate the potential of a carbohydrases-rich extract produced by SSF of BSG to enhance the nutritional value of plant-based diets for European seabass (Dicentrarchus labrax) juveniles. BSG was fermented by A. ibericus (MUM 03.49) to obtain an aqueous enzymatic extract (1178 and 8317 U g−1 cellulase and xylanase activity, respectively). A control (50% protein; 18% lipids) diet was formulated with 55% DM of plant feedstuffs (PF), and four other diets were formulated similarly to the control but including 0.4% and 0.8% DM of lyophilized extract (BSG-extract), corresponding to 4000 and 8000 U of cellulase kg−1 of diet, directly included in the diet (BSG4 and BSG8 diets) or used to pre-treat the PF mixture of the control diet (PreBSG4 and PreBSG8 diets). Pre-treatment of PF with BSG-extract increased three-fold the dietary reducing sugars content and two-fold the antioxidant activity than the control diet. Cellulase and xylanase activities were highest in diets including BSG-extract directly added than pre-treated PF diets. These diets were fed to European seabass (IBW = 22 ± 1 g) for 66 days. Dietary supplementation with BSG-extract, mixed in the diet or used as a pre-treatment of PF, did not affect growth performance and whole-body composition (p>0.05) of European seabass but increased feed efficiency (up to 18%; p<0.05) and protein utilization (up to 22%; p<0.05). Nitrogen retention and total alkaline proteases activity were higher in fish fed with the PreBSG4 and PreBSG8 diets (p<0.01) than with the BSG4 and BSG8 diets. In contrast, BSG4 and BSG8 diets increased plasma glucose and decreased cholesterol levels compared to the control (p<0.05).In conclusion, this work showed the effectiveness of an extract produced by SSF of BSG, with high carbohydrases activity, to enhanced feed and protein utilization by European seabass, without affecting growth performance. Moreover, using BSG-extract to pre-treat PF seems to be more effective in improving protein utilization than adding it directly to the diet. This study demonstrated the feasibility of BSG valorization through SSF to produce a functional additive for aquafeeds. The novel produced BSG-extract simultaneously contributes to the sustainability of resources in a circular economy approach and increases the nutritional value of plant feedstuffs.

Effect of dietary Spirulina ( Arthrospira platensis ) on the growth performance, immune‐related gene expression and resistance to Vibrio anguillarum in European seabass ( Dicentrarchus labrax )

This research was conducted to reveal the effects of dietary Spirulina (Arthrospira platensis) meal on the growth performance, immune responses and resistance against Vibrio anguillarum in European seabass (Dicentrarchus labrax). In the study, the fish (5.74 ± 0.02 g) were fed with control (C) and three different levels (1%, 2.5% and 5%) of Spirulina meal-containing diets (SP1, SP2.5 and SP5) for 60 days. The adaptive and innate immune responses of fish were determined every 30th day of the study. The results showed that respiratory burst activity (RBA) was significantly elevated on the SP2.5 and SP5 groups on the 30th day of the study. Lysozyme activity (LYS) was increased on the SP1 group on the 30th day and the SP5 group on the 60th day (p < 0.05). Myeloperoxidase activity (MPO) was raised on the 60th day of the SP2.5 and SP5 groups compared with the C (p < 0.05). IL-1β gene expression increased in the kidney and intestine of fish on the 30th day and in the spleen on the 60th day. IL-10 gene expression in the intestine of fish fed the Spirulina-containing diet was elevated at each sampling time relative to the C group (p < 0.05). Elevated IL-6 activity was determined in the kidney and the intestine on all Spirulina-fed groups compared with control at both sampling times. Similar to IL-6, IL-8 gene expressions were elevated in all Spirulina-fed groups (p < 0.05). TNF-α was up-regulated in the kidney and intestine of all Spirulina-fed groups compared with the C group on the 30th day of the study (p < 0.05). TGF-β gene expression was increased in the kidney and intestine of all Spirulina groups compared with the C group on all sampling times. COX-2 gene expression in the kidneys and intestines of fish fed with Spirulina diets was significantly elevated compared with the C diet at days 60th and 30th respectively. Hepcidin gene expression of all groups was elevated in all tissue samples on the 30th day of the study. The survival rate of fish infected with V. anguillarum was higher in all Spirulina-fed groups than in the C group. The feed conversion rate and protein efficiency ratio of fish fed with a 1% Spirulina diet was found to be better than those fed with other diets. These results show that up to the 5% inclusion of Spirulina meal in European seabass diets promotes some growth parameters and supports immunity in fish.

Potential application and beneficial effects of a marine microalgal biomass produced in a high-rate algal pond (HRAP) in diets of European sea bass, Dicentrarchus labrax

Microalgae have been used as live food in aquatic species. In recent years, the interest in microalgae has considerably increased, thanks to the evolution of production techniques that have identified them as an ecologically attractive aquafeed ingredient. The present study provides the first data about the effects of dietary inclusion of a microalgae consortium grown in a high-rate algal pond system on zootechnical performance, morphometric indices, and dietary nutrient digestibility as well as morphology and functionality of the digestive system of European sea bass, Dicentrarchus labrax. A dietary treatment including a commercial mono-cultured microalgae (Nannochloropsis sp.) biomass was used for comparison. Six hundred and thirty-six European sea bass juveniles (18 ± 0.28 g) were randomly allotted into 12 experimental groups and fed 4 different diets for 10 weeks: a control diet based on fish meal, fish oil, and plant protein sources; a diet including 10% of Nannochloropsis spp. biomass (100 g/kg diet); and two diets including two levels (10% and 20%) of the microalgal consortium (100 and 200 g/kg diet). Even at the highest dietary inclusion level, the microalgal consortium (200 g/kg diet) did not affect feed palatability and fish growth performance. A significant decrease in the apparent digestibility of dry matter, protein, and energy was observed in diets including 10 and 20% of the microalgal consortium, but all fish exhibited a well-preserved intestinal histomorphology. Moreover, dietary inclusion with the microalgal consortium significantly increased the enzymatic activity of maltase, sucrase-isomaltase, and ɤ-glutamil transpeptidase in the distal intestine of the treated European sea bass. Algal consortium grown using fish farm effluents represents an attempt to enhance the utilization of natural biomasses in aquafeeds when used at 10 % as substitute of vegetable ingredients in diet for European sea bass.