Search Results (127)

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs) that make farmed fish valuable to human health, given their bioactivity and highly unsaturated structure that also renders them exceptionally prone to oxidation during feed manufacture and storage, within the fish, and along the supply chain to the consumer. Preserving the oxidative stability, and hence the biological value, of these fatty acids is therefore a central challenge for sustainable aquaculture, made more acute by the replacement of omega-3-rich, oxidatively buffered fish oil with terrestrial oils that lower LC-PUFA content and shift the pro-/antioxidant balance of aquafeeds. Adopting an integrative feed-to-fish-to-consumer perspective, this review examines the strategies proposed to retain and protect EPA and DHA in farmed fish, distinguishing the physiological requirements of fish from the nutritional targets relevant to humans. We first appraise, comparatively, fish oil replacement, finishing diets and nutritional programming, showing that recovery of EPA and DHA is species-, tissue- and context-dependent and seldom complete, with EPA, a key eicosanoid precursor, preferentially catabolised. Through a focused, reproducible literature search, we then evaluate antioxidant-oriented nanoencapsulation as a means of shielding marine LC-PUFAs from oxidation and improving their stability and bioavailability. Although nanoencapsulation consistently enhances oxidative stability and, in the few in vivo studies available, fish performance, the evidence is constrained by heterogeneous and frequently incomplete physicochemical characterisation, scarce storage stability and in vivo data, and largely unaddressed safety, environmental-fate, regulatory, scalability and consumer-acceptance concerns. We conclude that protecting omega-3 oxidative stability will require combining well-characterised delivery systems with species-appropriate nutrition, and we set out the standardised characterisation, required in vivo validation, and integrated safety and life-cycle assessment needed to realise antioxidant-protective, nanotechnology-enabled aquafeeds. Full article

Δ9 fatty acyl desaturase (Δ9 FAD) exerts important regulatory effects on fatty acid metabolism and membrane fluidity. However, its existence and the effects of nutritional regulation and ambient salinity on its expression are currently unknown in mud crab (Scylla paramamosain). In this study, the full cDNA sequence of Δ9 fad was isolated from the hepatopancreas of mud crab, which consists of 1468 bp and encodes a polypeptide of 347 amino acids. Sequence analysis revealed that the protein possessed typical characteristics of Δ9 FAD including three histidine-rich domains (HRLWSH, HRVHH and HNYHH), four transmembrane regions and three conserved motifs (FFSHMGW, QRKYY and PWDY). The results of tissue distribution indicated that the mud crab’s Δ9 fad expression was enriched in the hepatopancreas, with relatively lower levels found in the thoracic ganglia and cranial ganglia. Δ9 fad expression in the hepatopancreas was significantly influenced by dietary fatty acid profiles, and the replacement of fish oil with soybean oil markedly downregulated the transcriptional levels of hepatopancreatic Δ9 fad. Furthermore, the transcriptional levels of Δ9 fad were also significantly affected by ambient salinity. Under chronic salinity stress, the 7‰, 12‰, 17‰ and 22‰ salinity groups showed higher transcriptional levels of Δ9 fad in the hepatopancreas than the 27‰ salinity group, and the 7‰ salinity group significantly differed from the 27‰ salinity group. Under the acute salinity stress condition, the Δ9 fad transcriptional levels of muscle in the 14‰ and 4‰ salinity groups were higher than those in the 24‰ salinity group at 6 h and 12 h. By contrast, Δ9 fad in the hepatopancreas exhibited a slow response in reaction to low salinity stress, and only the 4‰ salinity group at 96 h had a higher value than the 24‰ salinity group. In addition, as for the starvation stress experiment, Δ9 fad expression in the starvation group was dramatically reduced when compared with the feeding group. These findings improve our understanding of the physiological roles of Δ9 fad and its regulatory mechanisms in crustaceans. Full article

This study evaluated the use of finishing diets to reduce fish oil (FO) inclusion in European sea bass feeds while preserving fillet quality and n-3 fatty acid content. Fish (197 g) were fed for 25 weeks with a control FO diet, based on 9% FO and 6% plant oil, or diets where 6% FO was replaced by rapeseed oil (RO) or microalgae (AO; Nannochloropsis sp. and Schizochytrium sp.). After 13 weeks, 2 groups of fish fed the RO diet were switched to the FO or AO finishing diets for the final 12 weeks. Growth, feed efficiency, body composition, and health were unaffected by dietary treatments. However, long-term RO feeding reduced eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA) and increased monounsaturated and n-6 fatty acids compared to fish fed AO or FO. A 12-wk FO finishing diets shifted morphometric traits, fatty acid profiles, liver histology, and overall fish quality of fish previously fed with RO toward those of fish continuously fed FO, whereas the AO finishing diet produced a smaller shift. Longer finishing periods may further enhance fillet quality when using microalgae-based oils. Full article

The search for sustainable alternatives to fish oil (FO) in aquafeeds is imperative for the long-term sustainability of aquaculture. This study evaluated the effects of partially replacing FO with oils derived from Hermetia illucens (RH) and Musca domestica (RY) larvae at 10%, 30%, and 50% levels on growth, lipid metabolism, hepatic antioxidant capacity, and gut microbiota in juvenile Cyprinus carpio. Results showed distinct source- and dose-dependent responses. RY produced a consistent dose-dependent trend in growth parameters, whereas RH exhibited a biphasic pattern, with growth impairment at 30% replacement and recovery at 50%. Both oils significantly suppressed hepatic fatty acid synthase (FAS) activity, yet this suppression was accompanied by dose-dependent up-regulation of fas expression, particularly at high RH and RY levels, indicating complex post-transcriptional regulation. RH at higher replacement levels reduced digestive enzyme activities and antioxidant capacity, while higher RY caused minimal disruption. Both oils reshaped gut microbiota toward oil-specific community structures. Two-way ANOVA revealed significant synergistic interactions between oil source and replacement level for most serum biochemical and hepatic antioxidant parameters (ηp² > 0.90). These findings demonstrate that RY is a tolerable alternative across a wide replacement range, though all RY groups exhibited lower growth than the control, 30% is identified as the maximum tolerable level; whereas RH requires precise dosing at 10% to avoid the 30% impairment threshold. Full article

Leptobotia elongata, an endangered freshwater fish endemic to the upper Yangtze River, increasingly depends on artificial reproduction for conservation. However, a captive juvenile population fed a conventional diet commonly exhibits ovarian development arrested at stages I–II, representing a critical bottleneck for captive reproduction. To address this, juvenile L. elongata were reared for 6 months on either a basal diet (control group, CG) or a lipid-enriched diet in which soybean oil was replaced by fish oil and soybean lecithin, with vitamin E added (treatment group, TG). Histological examination revealed that TG ovaries advanced from stage I–II to stage III, with markedly larger oocytes and centralized nucleoli. LC-MS/MS-based untargeted metabolomics profiling identified 1773 metabolites, of which 566 differed significantly between groups (374 up- and 192 down-regulated in TG). KEGG enrichment revealed 15 significantly perturbed pathways, with nucleotide metabolism showing the highest enrichment (Rich factor = 0.22), accompanied by changes in fatty acid biosynthesis, biosynthesis of unsaturated fatty acids, glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, pantothenate and CoA biosynthesis, and TCA-related modules. Coordinated up-regulation of long-chain polyunsaturated fatty acids (DHA, EPA, ARA, α-linolenic acid), DHA-phosphatidylethanolamine, phosphatidylcholine and CDP-choline, together with depletion of their precursors (sn-glycerol-3-phosphate, LPI(20:4), pyrophosphate), was consistent with enhanced phospholipid remodeling and Lands-cycle activity. A multi-tier regulatory network was constructed, anchored on three pathway hubs (nucleotide metabolism, pyrimidine metabolism and fatty acid elongation) and five functional modules. This network indicated that dietary lipid supplementation was associated with coordinated changes across four interconnected metabolic axes: lipid supply and membrane remodeling, nucleotide synthesis and turnover, amino acid–protein translation, and energy–coenzyme metabolism. Collectively, these findings propose a metabolic framework and identify candidate biomarkers (e.g., DHA-PE, PC) for optimizing feed formulations of L. elongata. Full article

Marine by-products, including fishery discards, seafood-processing residues, aquaculture wastes, crustacean shells, and seaweed-derived side streams, are heterogeneous feedstocks rich in proteins, lipids, minerals, chitinous materials, polysaccharides, and bioactive compounds. This review examines insect-mediated bioconversion as a controlled biorefinery strategy for transforming these unstable marine residues into functional aquafeed ingredients and value-added bioproducts. We compare major marine feedstock classes and industrially relevant insects, with emphasis on substrate–insect matching, moisture control, salinity, lipid and ash load, texture, spoilage risk, and safety. Particular attention is given to how marine substrates can tailor insect meal, insect oil, chitinous fractions, hydrolysates, frass, and functional feed additives. The review further summarizes aquafeed applications of insect-derived products, including fishmeal and fish-oil replacement, protein and amino acid quality, lipid enrichment, gut health, immunity, and disease resistance in aquatic animals. Microbiome-assisted strategies, such as fermentation, enzymatic pretreatment, and gut or substrate microbial management, are discussed as tools to improve substrate stability, digestibility, and product quality. Finally, safety, regulation, scale-up, life cycle assessment, and techno-economic issues are considered. Overall, marine insect biorefineries should be optimized not only for biomass yield, but also for product quality, traceability, and application-specific safety. Full article

Reducing reliance on supplemental fish oil is central to sustainable aquaculture, but the molecular consequences of replacing it with vegetable oils remain poorly characterized in the juvenile Chinese soft-shelled turtle (Pelodiscus sinensis). We evaluated whether full substitution of the supplemental dietary fish oil (FO) with linseed oil (LO) or soybean oil (SO) compromises hepatic lipid metabolism in Pelodiscus sinensis. Three isonitrogenous and isolipidic diets, sharing identical fish meal and other ingredient bases and differing only in the supplemental lipid (4% FO, LO or SO), were fed to triplicate groups of juvenile turtles (initial body weight 55.0 ± 0.05 g) for 8 weeks. Growth performance, survival, feed conversion ratio, and serum biochemistry were unaffected. However, both vegetable oil diets altered tissue fatty acid composition, raising n-6 PUFA and lowering n-3 LC-PUFA and the n-3/n-6 ratio in liver and muscle (muscle EPA and DHA each decreased by approximately 40%); the SO group additionally exhibited elevated hepatic malondialdehyde, whereas hepatic lipid droplet area and lipid content did not differ significantly among groups. Liver transcriptomic profiling identified 262 (LO vs. FO) and 214 (SO vs. FO) differentially expressed genes, converging on lipid storage and bile acid metabolism. RT-qPCR confirmed the up-regulation of PLIN3, G0S2 and APOF and the down-regulation of CYP7A1. Over 8 weeks, replacement of supplemental FO maintained growth without overt impairment while altering tissue fatty acid profiles and the hepatic expression of key lipid metabolism genes. Full article

The replacement of fishmeal (FM) in aquafeeds for carnivorous fish remains challenging due to reduced palatability and adverse effects on liver health and intestinal microbiota. Marine by-products-based additives containing fish protein hydrolysates and seaweed polysaccharides have shown potential to overcome these limitations. This study evaluated the effects of graded supplementation of Haiweisu (HWS), a multi-marine by-product formulated with squid viscera hydrolysate, small-molecule components from fish protein hydrolysate, seaweed polysaccharides, and seaweed residue as a carrier, in a FM-free diet for juvenile largemouth bass. Four isonitrogenous and isolipidic diets were prepared: a FM-free control diet (CON) and three diets supplemented with 10, 20, or 30 g/kg HWS (designated S10, S20, and S30, respectively). Each diet was fed to triplicate groups of fish (29.26 ± 2.61 g) for 56 days. Results showed that HWS supplementation linearly increased final body weight, weight gain rate, and feed intake, while significantly reducing the feed conversion ratio (p < 0.05). All HWS-supplemented groups exhibited markedly lower hepatic lipid accumulation and plasma total cholesterol levels compared with the CON group, accompanied by alleviated hepatocellular steatosis and inflammatory infiltration as revealed by Oil Red O and H&E staining. Moreover, HWS significantly enhanced intestinal microbiota alpha diversity (Ace, Chao, Sobs, and Shannon indices), decreased the relative abundance of the dominant genus Mesomycoplasma, and enriched potentially beneficial genera including Methylobacterium, Delftia, and Sphingomonas (p < 0.05). In conclusion, dietary HWS supplementation effectively improved growth performance, alleviated hepatic steatosis and inflammation, and beneficially reshaped the intestinal microbiota in juvenile largemouth bass fed a FM-free diet. These findings support HWS as a promising functional additive for sustainable FM-free aquafeeds in carnivorous fish species. Full article

The goal of this Special Issue was to collect the latest research results on the topics of (1) the physiological response of fish to various stressful situations and nutritional changes, (2) the replacement of fish meal and fish oil with sustainable, alternative protein and lipid sources in fish feeds, and (3) supplementing fish feeds with various additives in order to enhance the immune response and increase the stress and disease resistance of fish reared in intensive systems. These topics are very important for the development of a more effective and sustainable intensive aquaculture, as fish farming systems are becoming more intensive and industrialized, which results in a more stressful environment for farmed fish. Another important challenge is providing enough high-quality fish feed to fulfill the increasing demand of intensive aquaculture. There are 14 original research articles published in this Special Issue. The authors come from a wide array of countries, and they worked with a wide variety of freshwater and marine fish species, which are important for intensive aquaculture. These articles represent only a modest contribution to the overall literature of stress and nutritional physiology of farmed fish. However, each of these papers contain interesting new information regarding the solution of the two major problems of intensifying aquaculture: environmental stresses and nutrition management. Full article

Background/Objectives: In gilthead seabream, the transition from fish meal/oil-based diets to diets with partial plant-based replacement is gaining ground due to price fluctuations and environmental concerns. Most studies focus on the dietary effects on important commercial traits such as body weight and fat deposition, while metabolic traits and their underlying genetic and transcriptional regulation remain largely unexplored. Methods: In the present study, the response of metabolic traits (protein, cholesterol, and triglycerides levels) was measured in gilthead seabream of different genetic backgrounds at 15 (D15) and 30 days (D30) after a shift from a fish meal/oil-based diet (FM) to a plant-based (PP) diet. Results: Moderate heritability of total protein and triglyceride content of blood was estimated on D30. Significantly positive genetic correlations were observed between triglyceride D30 content and final weight and muscle fat. No significant genotype-by-diet interaction effects were detected. At the end of the production cycle, final body weight and fat were recorded, and hepatic expressions of ghri, ghrii, igf1 and ttr genes were measured in a subpopulation of 160 fish. An overall negative correlation was recorded between the hepatic expression of igf1 and final weight, whereas strong positive correlations were observed between the expression of all hepatic genes measured. In the same population, fourteen SNPs located in the 3′ UTR of ghrii and igf1 genes were genotyped and analyzed in two ways, as a sum-of-risk score and individually as predictors for body weight, muscle fat, metabolic traits and hepatic expression levels. The sum-of-risk score was significantly associated with muscle fat and ttr expression. Studying the effect of each SNP independently, two SNPs in the igf1 gene were associated with ghrii expression levels and one SNP in igf1 gene was associated with triglyceride levels at day 15 (Trigl_D15) while one SNP in ghrii was associated with ttr expression levels. Focusing on the diet, it was significantly associated with final weight, muscle fat, protein (D30) and triglycerides levels, and hepatic expression levels of ghrii. Full article

Background: Supplementing aquafeeds with emulsifiers can enhance lipid utilization, yet the physiological effects of lysolecithin, derived from enzymatic lecithin conversion, remain under-explored. Objectives: This study examined the effects of lysolecithin supplementation on hepatopancreatic transcriptome and gut microbiota in largemouth bass (Micropterus salmoides) fed stearin-based high-lipid diets. Methods: Two diets were formulated: a control containing 130 g kg⁻¹ stearin fish oil (SO), and in the experimental diet (SL), 3.1 g kg⁻¹ rapeseed oil was replaced with 3.1 g kg⁻¹ lysolecithin oil. Each diet was fed to three replicate groups for 56 days. Hepatopancreas and distal intestine were sampled for transcriptome profiling, and gut microbiota were characterized at 28 and 56 days. Results: Lysolecithin supplementation resulted in 424 differentially expressed genes compared with the control (322 up- and 102 downregulated). KEGG enrichment indicated major effects on lipid metabolic processes, notably activation of the PI3K-AKT signaling pathway, enhanced adipocyte lipolysis, and modulation of adipocytokine signaling, suggesting improved insulin sensitivity and lipid mobilization. Histological analysis showed mild distal intestinal inflammation in the SO group. Gut microbiota composition shifted over time; lysolecithin increased the relative abundance of Cetobacterium and reduced potential opportunistic taxa compared with the control. Conclusions: Overall, dietary inclusion of lysolecithin improved lipid utilization in largemouth bass, likely by enhancing lipid metabolism and promoting beneficial gut microbial profiles. These findings support lysolecithin as a promising feed additive for optimizing high-lipid aquafeeds. Full article

Recently, polyhydroxyalkanoates (PHAs) have gained significant attention as a bioactive material for replacing petrochemical plastics. PHAs can be produced by microorganisms growing on sludge substrates. In this study, fish-processing wastewater was investigated as an alternative substrate for PHA production using Bacillus cereus. Wastewater dilution, carbon-to-nitrogen ratio modification, and the addition of fish oil as a lipidic substrate were examined, and bacterial growth and biopolymer production were optimized. First, wastewater was diluted (25–100%) and examined. The 50% dilution treatment was selected, yielding a CDM of 0.426 g/L and a PHA content of 6.69%. In subsequent steps, the effects of wastewater fermentation and bacterial adaptation prior to the main production processes were investigated. According to the results, the 50% and 100% fermented treatments exhibited higher CDM values (0.970–1.022 g/L) compared to the non-fermented treatments. Cultures inoculated with adapted bacteria showed superior performance (CDM: 1.455 g/L, PHA: 0.499 g/L, PHA content: 34.63%) relative to non-adapted treatments. The effect of the carbon-to-nitrogen (C/N) ratio was also optimized by supplementing two carbon sources: glucose and crude fish oil. The optimal treatment T1 (effluent + 0.6 g/L glucose) had a CDM of 1.32 g/L and a PHA content of 0.215 g/L. Treatment 1, which consisted solely of effluent and fish oil, exhibited higher values (CDM: 1.12 g/L, PHA: 0.65 g/L) and was therefore considered the cost-effective treatment. Subsequently, a scale-up process was conducted in a 4 L bioreactor over 300 h under semi-continuous, long-term cultivation. The optimal harvesting time for the biopolymer was achieved during the fourth cycle (180–240 h). The produced biopolymer was characterized using FTIR, NMR, TGA, DSC, SEM, and XRD analyses, confirming the production of a copolymer, specifically poly(3-hydroxybutyrate-co-3-hydroxyvalerate). This study used wastewater from the fish industry for the production of biodegradable polyhydroxyalkanoates. Full article

Research designed to reduce or eliminate fishmeal (FM) in trout feeds, for reasons that have changed over time, has been conducted for over a century. Reducing the dependency on FM remains one of the most urgent issues facing the industry. Feed represents the most expensive operational cost of fed aquaculture, and is responsible for ecosystem disturbance following nutrient discharges. Rainbow trout, the second most farmed salmonid globally, can be raised completely without FM or fish oil (FO), with its growth and efficiency not differing from trout fed FM-based feeds. However, ingredient choice and nutrient supplementation strongly influence physiological responses, efficiency, and long-term outcomes. As land animal proteins are increasingly used in place of FM, both with and void of dietary FO, their distinct biological effects warrant focused evaluation. Although numerous studies have synthesized findings across various alternative protein categories including those with insect proteins and animal by-products, this literature is widely disseminated and sometimes difficult to access. The present contribution focuses on terrestrial/aerial animal proteins that have been used to totally replace FM in rainbow trout feeds. Attention is given to their effects on physiological control processes that may influence production efficiency. Areas worthy of future study are identified and include long-term performance and health dynamics, the refinement of nutritional and formulation strategies, and the broader evaluation of biological interactions and system-level outcomes. Full article

Aquaculture sustainability requires a reduction in the reliance on marine-derived raw materials such as fish oil in aquafeeds while maintaining fish health and product quality. This study investigated the effects of replacing fish oil with plant oils supplemented with DHA-rich Schizochytrium limacinum biomass on the gut microbiota of European sea bass (Dicentrarchus labrax). S. limacinum SR21—an oleaginous microalga naturally rich in omega-3 fatty acids—was produced through heterotrophic fermentation using crude glycerol, a waste stream from biodiesel production, within a circular economy framework. A 21-week feeding trial was conducted in an indoor recirculating aquaculture system using 280 fish distributed across eight tanks. Four experimental diets were tested: fish oil-based (FO), plant oil-based without microalga (VO + 0), and plant oil-based supplemented with 5% (VO + 5) or 10% (VO + 10) microalgal biomass. Gut microbiota was analyzed in 22 fish per group using 16S rRNA gene sequencing. While alpha and beta diversity analyses of gut microbiota revealed modest structural shifts at phylum and class ranks, genus-rank differences were evident, with Lactobacillus and Clostridium sensu stricto associated with FO and VO + 0 diets, and Pseudomonas and Staphylococcus enriched in microalga-supplemented groups. Functional inference highlighted enhanced bile acid biosynthesis and carbohydrate metabolism in VO + 0, whereas antioxidant-related pathways, including ubiquinone and carotenoid biosynthesis, were stimulated in VO + 5 and VO + 10 groups. These results demonstrate that S. limacinum biomass modulates microbiota functional capacity, potentially contributing to oxidative stress mitigation and host resilience. The findings support microbiota-informed feed formulation strategies to advance sustainable aquaculture. Full article