Metabolic Effect of Dietary Taurine Supplementation on Nile Tilapia (Oreochromis nilotictus) Evaluated by NMR-Based Metabolomics

New alternative ingredients and genetic selection are the next game changers in rainbow trout nutrition: a metabolomics appraisal

The formulation of sustainable fish feeds based on plant ingredients supplemented by alternative ingredients to plant (insect, micro-algae, yeast) and genetic selection of fish for plant-based diets were tested on rainbow trout in two separate experiments. Plant-based diets and corresponding diets supplemented with an ingredient mix: insect, micro-algae and yeast in Experiment A, and insect and yeast in Experiment B were compared to commercial-like diets. In experiment A, the mix-supplemented diet was successful in compensating the altered growth performance of fish fed their respective plant-based diet compared to those fed the commercial diet, by restoring feed conversion. In experiment B, the selected line demonstrated improved growth performances of fish fed mix-supplemented and plant-based diets compared to the non-selected line. Metabolomics demonstrated a plasma compositional stability in fish fed mix-supplemented and basal plant-based diets comprising an amino acid accumulation and a glucose depletion, compared to those fed commercial diets. The selected line fed mix-supplemented and commercial diets showed changes in inositol, ethanol and methanol compared to the non-selected line, suggesting an involvement of microbiota. Changes in plasma glycine-betaine content in fish fed the mix-supplemented diet suggest the ability of the selected line to adapt to alternative ingredients.

Compound-Specific 1D 1H NMR Pulse Sequence Selection for Metabolomics Analyses

NMR-based metabolomics approaches have been used in a wide range of applications, for example, with medical, plant, and marine samples. One-dimensional (1D) ¹H NMR is routinely used to find out biomarkers in biofluids such as urine, blood plasma, and serum. To mimic biological conditions, most NMR studies have been carried out in an aqueous solution where the high intensity of the water peak is a major problem in obtaining a meaningful spectrum. Different methods have been used to suppress the water signal, including 1D Carr-Purcell-Meiboom-Gill (CPMG) presat, consisting of a T₂ filter to suppress macromolecule signals and reduce the humped curve in the spectrum. 1D nuclear Overhauser enhancement spectroscopy (NOESY) is another method for water suppression that is used routinely in plant samples with fewer macromolecules than in biofluid samples. Other common 1D ¹H NMR methods such as 1D ¹H presat and 1D ¹H ES have simple pulse sequences; their acquisition parameters can be set easily. The proton with presat has just one pulse and the presat block causes water suppression, while other 1D ¹H NMR methods including those mentioned above have more pulses. However, it is not well known in metabolomics studies because it is used only occasionally and in a few types of samples by metabolomics experts. Another effective method is excitation sculpting to suppress water. Herein, we evaluate the effect of method selection on signal intensities of commonly detected metabolites. Different classes of samples including biofluid, plant, and marine samples were investigated, and recommendations on the advantages and limitations of each method are presented.

An NMR-Based Metabolomics Assessment of the Effect of Combinations of Natural Feed Items on Juvenile Red Drum, Sciaenops ocellatus

This study evaluated the effects of seven diets composed of natural feed components (chopped fish, shrimp, and squid) alone or in combination on the liver metabolite profile of juvenile red drum (Sciaenops ocellatus) cultured in a 24-tank recirculating aquaculture system over the course of 12 weeks using Nuclear Magnetic Resonance (NMR)-based metabolomics. Experimental diets included fish (F), shrimp (SH), squid (SQ), fish and shrimp (FSH), fish and squid (FSQ), shrimp and squid (SHSQ), fish, shrimp, and squid (FSHSQ). A commercial fishmeal-based pelleted diet was used as a control. Fish were fed isocalorically. Red drum liver samples were collected at five different time points: T0, before the start of the trial (n = 12), and subsequently every 3 weeks over the course of 12 weeks (T3, T6, T9, T12), with n = 9 fish/diet/time point. Polar liver extracts were analyzed by NMR-based metabolomics. Multivariate statistical analyses (PCA, PLS-DA) revealed that red drum fed the F diet had a distinct liver metabolite profile from fish fed the other diets, with those fed SH, SQ and the combination diets displaying greater similarities in their metabolome. Results show that 19 metabolites changed significantly among the different dietary treatments, including amino acids and amino acid derivatives, quaternary amines and methylamines, carbohydrates and phospholipids. Specifically, γ-butyrobetaine, N-formimino-L-glutamate (FIGLU), sarcosine and beta-alanine were among the most discriminating metabolites. Significant correlations were found between metabolites and six growth performance parameters (final body weight, total length, condition factor, liver weight, hepatosomatic index, and eviscerated weight). Metabolites identified in this study constitute potential candidates for supplementation in fish feeds for aquaculture and optimization of existing formulations. Additionally, we identified a quaternary amine, γ-butyrobetaine as a potential biomarker of shrimp consumption in red drum. These results warrant further investigation and biomarker validation and have the potential for broader applicability outside of the aquaculture field in future investigations in wild red drum populations and potentially other carnivorous marine fishes.

Identification of characteristic volatiles and metabolomic pathway during pork storage using HS-SPME-GC/MS coupled with multivariate analysis

Previous researches have been conducted evaluating the volatile compounds of pork. However, data regarding the changes in volatiles and metabolic pathways during pork storage were inadequately investigated. Herein, a headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC/MS) coupled multivariate analysis was proposed for characterizing the profiles of volatile compounds and metabolic pathways during pork storage. A total of 37 metabolites, including aldehydes, ketones, alcohols etc. were successfully identified. Multivariate statistical analysis revealed a substantial variation in metabolite phenotype among samples over the pork storage period, with 12 characteristic metabolites and 5 potential characteristic metabolites screened as biomarkers. Moreover, three metabolomic pathways analysis and transformation between each other (thermal reactions, lipid metabolism and amino acid metabolism) reveals the underlying mechanisms of metabolites change of pork. Therefore, the present study may provide insight into future understanding of the variation in the pork metabolite profiles.

Long-term exposure to polyethylene microplastics and glyphosate interferes with the behavior, intestinal microbial homeostasis, and metabolites of the common carp (Cyprinus carpio L.)

Polyethylene microplastics (PE-MPs) and glyphosate (GLY) occur widely and have toxic characteristics, resulting in increased research interest. In this study, common carp were used to assess the individual and combined toxicity of PE-MPs (0, 1.5, or 4.5 mg/L) and GLY (0, 5, or 15 mg/L) on the brain-gut axis. After 60 days of exposure, the developmental toxicity, blood-brain barrier (BBB), locomotor behavior, intestinal barrier (physical barrier, chemical barrier, microbial barrier), and intestinal content metabolism of common carp were evaluated. Results showed that 15 mg/L of GLY exposure significantly reduced the mRNA expression of tight-junction genes (occludin, claudin-2, and ZO-1) in the brain, and acetylcholinesterase (AChE) activity was clearly inhibited by high concentrations of GLY. However, different concentrations of PE-MPs had no significant effect on the activity of AChE. Furthermore, the free-swimming behavior of common carp was distinctly inhibited by treatment with a combination of 15 mg/L GLY and 4.5 mg/L PE-MPs. Histological studies indicated that PE-MPs alone and in combination with GLY could disrupt the physical and chemical intestinal barriers of common carp. Additionally, the abundance and diversity of gut microbiota in common carp were significantly changed when exposed to a combination of PE-MPs and GLY. Metabolomics further revealed that PE-MPs combined with GLY triggered metabolic changes and that differential metabolites were related to amino acid and lipid metabolism. These findings illustrate that exposure to PE-MPs or GLY alone is toxic to fish and results in physiological changes to the brain-gut axis. This work offers a robust analysis to understand the mechanisms underlying GLY and MP-induced aquatic toxicity.

Exploring the Biotechnological Value of Marine Invertebrates: A Closer Look at the Biochemical and Antioxidant Properties of Sabella spallanzanii and Microcosmus squamiger

Sabella spallanzanii and Microcosmus squamiger were profiled for proximate composition, minerals, amino acids, fatty acids (FA), carotenoids, radical scavenging activity on the 2,2-diphenyl-1- picrylhydrazyl (DPPH) radical, oxygen radical absorbance capacity (ORAC) and iron and copper chelating properties. Microcosmus squamiger had the highest level of moisture and crude protein, S. spallanzanii was enriched in crude fat and ash. Both species had similar levels of carbohydrates and energy. There was a prevalence of arginine and glycine in S. spallanzanii, and of taurine in M. squamiger. The most abundant minerals in both species were Na, Ca, and K. The methanol extract of S. spallanzanii had metal chelating properties towards copper and iron, while the methanol extract of M. squamiger was able to chelate copper. M. squamiger extracts had similar ORAC values. Fucoxanthinol and fucoxanthin were the major carotenoids in the M. squamiger dichloromethane extract. Saturated FA were more abundant than unsaturated ones in methanol extracts, and unsaturated FA prevailed in the dichloromethane extracts. Palmitic acid was the predominant FA in methanol extracts, whereas eicosapentaenoic (EPA) and dihomo-γ-linolenic acids were the major compounds in dichloromethane extracts. Low n-6/n-3 ratios were obtained. Our results suggests that both species could be explored as sources of bioactive ingredients with multiple applications.

Effects of Dietary Protein Level on the Gut Microbiome and Nutrient Metabolism in Tilapia (Oreochromis niloticus)

Dietary protein is one of the most important nutritional factors in aquaculture. The aim of this study was to examine the effects of dietary protein levels on the gut microbiome and the liver and serum levels of metabolites in tilapia. Tilapia were fed a diet with a low (20%), moderate (30%), or high (40%) content of crude protein, and the homeostasis of the gut microbiome and metabolic profile of the liver and serum were analyzed. The results showed no significant differences in the diversity and richness of the gut microbiome among the groups; however, there were differences in the microbial composition of the gut. The metabolome analysis of liver samples revealed a difference in the glucose level among the groups, with the highest glucose level in fish fed a high protein diet. In addition, there were significant differences in the levels of tyrosine, guanosine, and inosine among the metabolome analysis of serum samples of these groups. In summary, diets with different protein levels could affect the composition of gut microbiota and the dynamic balance of microbial communities. Dietary protein content can also affect glycolysis and amino acid metabolism in tilapia.

Putative imbalanced amino acid metabolism in rainbow trout long term fed a plant-based diet as revealed by 1H-NMR metabolomics

The long-term effect of a plant (P)-based diet was assessed by proton nuclear magnetic resonance (¹H-NMR) metabolomics in rainbow trout fed a marine fish meal (FM)-fish oil (FO) diet (M), a P-based diet and a control commercial-like diet (C) starting with the first feeding. Growth performances were not heavily altered by long-term feeding on the P-based diet. An ¹H-NMR metabolomic analysis of the feed revealed significantly different soluble chemical compound profiles between the diets. A set of soluble chemical compounds was found to be specific either to the P-based diet or to the M diet. Pterin, a biomarker of plant feedstuffs, was identified both in the P-based diet and in the plasma of fish fed the P-based diet. ¹H-NMR metabolomic analysis on fish plasma and liver and muscle tissues at 6 and 48 h post feeding revealed significantly different profiles between the P-based diet and the M diet, while the C diet showed intermediate results. A higher amino acid content was found in the plasma of fish fed the P-based diet compared with the M diet after 48 h, suggesting either a delayed delivery of the amino acids or a lower amino acid utilisation in the P-based diet. This was associated with an accumulation of essential amino acids and the depletion of glutamine in the muscle, together with an accumulation of choline in the liver. Combined with an anticipated absorption of methionine and lysine supplemented in free form, the present results suggest an imbalanced essential amino acid supply for protein metabolism in the muscle and for specific functions of the liver.

Effect of dietary taurine supplementation on metabolome variation in plasma of Nile tilapia

Taurine has been considered as an essential nutrient for many aquaculture species. While dietary taurine supplementation is highly recommended, novelty studies on taurine metabolism in fish are needed. The present study aimed to provide insight into the molecular mechanisms involved in multiple metabolome changes in Nile tilapia (Oreochromis niloticus) by studying plasma metabolic profile changes in response to graded levels of dietary taurine supplementation. The analysis used proton nuclear magnetic resonance-based metabolomics. Four groups of tilapias were fed with four diets supplemented with 0.0, 0.4, 0.8 and 1.2% taurine for 84 days. Fish plasma was sampled at multiple time points to provide an accurate snapshot of specific metabolic profiles during growth. Under the effect of taurine supplementation, 21 and 12 metabolites in tilapia plasma shown significant changes in terms of time-dependence and diet-dependence, respectively. These metabolic changes in tilapia plasma were mainly associated with energy and amino acid metabolism, lipids, nucleotides and protein metabolism. The results indicate that 0.8% taurine supplementation could significantly improve the carbohydrate synthesis, protein digestion and absorption, and fat deposition of tilapia and thereby promoted growth and development of tilapia.

What metabolic, osmotic and molecular stress responses tell us about extreme ambient heatwave impacts in fish at low salinities: The case of European seabass, Dicentrarchus labrax

Unprecedented shifts in temperature and precipitation patterns in recent decades place multiple abiotic stressors on the fish. In teleosts, metabolic, osmoregulatory, and molecular potential as tolerance responses to extreme ambient heatwave events at different salinities are poorly understood. The study was performed to evaluate the physio-biochemical stress responses and acclimation potential of European seabass, Dicentrarchus labrax maintained at four different salinities followed by an extreme ambient heatwave exposure. Fish were kept at 32, 12, 6, and 2 psu for 35 days followed by a simulated extreme ambient heatwave (33 °C) exposure for 10 days. Fish growth performances, physio-biochemical and molecular responses were recorded. Fish acclimated at 32 and 2 psu exhibited significantly (p < 0.05) decreased growth performance. Serum [Na⁺] and [Cl^-] ions were significantly lowered (p < 0.05) in 32 psu fish on day 10 of heatwave exposure. While serum glucose, triglycerides, and protein tended to decrease during the extreme ambient heatwave exposure, lactate content increased significantly (p < 0.05) in 32 psu fish on day 10. In 32 and 2 psu fish, serum metabolic enzymes, and cortisol levels increased significantly (p < 0.05) during the extreme heatwave exposure. On days 5 and 10, HSP70 mRNA was significantly (p < 0.05) upregulated in kidneys and gills of 32 and 2 psu fish, while Igf1 showed downregulation. In gills of 2 psu fish, ATPase Na⁺/K⁺-α1 and NKCC1 expression decreased significantly (p < 0.05) in 2 psu, in contrast, significant upregulation was observed at 32 psu fish during extreme ambient heatwave exposure. On days 5 and 10, cystic fibrosis transmembrane conductance (CFTR) upregulation was significantly lower (p < 0.05) in 32 and 2 psu fish. Results suggest that European seabass held at 12 and 6 psu water fare better physiological fitness during the tested extreme ambient heatwave event (33 °C), providing possible insights into options for future aquaculture management in a warming environment.

Supplementation of AQUAGEST® as a Source of Medium-Chain Fatty Acids and Taurine Improved the Growth Performance, Intestinal Histomorphology, and Immune Response of Common Carp (Cyprinus carpio) Fed Low Fish Meal Diets

Four diets were prepared to include a mixture of medium-chain fatty acids and taurine as a digestive/ metabolic enhancer (DME, AQUAGEST®) at 0, 1, 2, and 3 g DME/kg diet and fed to common carp (initial weight, 4.55±0.03 g) for 70 days. Dietary DME significantly increased the final weight, weight gain, specific growth rate, feed intake, and protein efficiency and decreased feed conversion ratio in a dose-dependent manner (P<0.05). The body lipid composition was significantly improved by feeding DME at 2 g/kg diet (P=0.0141). The intestine villus length and the number of goblet cells were significantly increased in fish fed 2 g DME/kg diet (P<0.05). The intestinal villi displayed increased length, branching, and density by supplementing DME to common carp diets. Fish fed DME at 2 g/kg diet displayed markedly decreased aspartate aminotransferase (AST) and alanine aminotransferase (ALT ) (P=0.025 and P=0.043) and increased total protein and globulin (P =0.002 and P=0.003). Additionally, fish fed 2 and 3 g DME/kg levels displayed significantly increased albumin levels (P=0.006). Lysozyme and phagocytic activities were increased by feeding DME at 2 g/kg diet, while the phagocytic index increased by 2 and 3 g/kg diet (P<0.05). The optimal supplementation level of DME is 1.63 to 2.05 g/kg for common carp based on the polynomial regression analysis. In conclusion, common carp fed diets with a mixture of medium-chain fatty acids and taurine displayed improved growth, digestion activity, and immune response.

Proton-NMR Metabolomics of Rainbow Trout Fed a Plant-Based Diet Supplemented with Graded Levels of a Protein-Rich Yeast Fraction Reveal Several Metabolic Processes Involved in Growth

BACKGROUND

Plant raw materials are commonly used in aquafeeds, as marine resources are unsustainable. However, full plant-based diets lead to poorer fish growth performance.

OBJECTIVE

We aimed to understand the metabolic effects of a yeast fraction as a protein supplement in a plant-based diet and to integrate such effects with phenotypic traits as a new approach to assess the interest of this raw material.

METHODS

Juvenile (49 g) rainbow trout (Oncorhynchus mykiss) were fed graded levels of a yeast protein-rich fraction (5% YST05, 10% YST10, 15% YST15) in a plant-based diet (PB) for 84 d. Final body weight, feed conversion ratio, and hepatosomatic and viscerosomatic indexes were measured. Plasma, liver, and muscle 1H-NMR fingerprints were analyzed with principal component analyses, and their metabolite patterns were clustered according to the yeast level to identify concomitant metabolic effects. A regression modeling approach was used to predict tissue metabolite changes from plasma fingerprints.

RESULTS

In tissues, the patterns of metabolite changes followed either linear trends with the gradual inclusion of a yeast fraction (2 patterns out of 6 in muscle, 1 in liver) or quadratic trends (4 patterns in muscle, 5 in liver). Muscle aspartate and glucose (395 and 138% maximum increase in relative content compared with PB, respectively) revealing modification in energy metabolism, as well as modification of liver betaine (163% maximum increase) and muscle histidine (57% maximum decrease) related functions, indicates that the yeast fraction could improve growth in several ways. The highest correlation between measured and predicted metabolite intensities in a tissue based on plasma fingerprints was observed for betaine in liver (r = 0.80).

CONCLUSIONS

These findings herald a new approach to assess the plurality of metabolic effects induced by diets and establish the optimal level of raw materials. They open the way for using plasma as a noninvasive matrix in trout nutrition studies.

Integrative Metabolomics for Assessing the Effect of Insect (Hermetia illucens) Protein Extract on Rainbow Trout Metabolism

Nutrition of high trophic species in aquaculture is faced with the development of sustainable plant-based diets. Insects seem particularly promising for supplementing plant-based diets. However, the complex effect of whole insect meal on fish metabolism is not well understood, and even less is known about insect meal extracts. The purpose of this work was to decipher the metabolic utilization of a plant-based diet supplemented with the gradual addition of an insect protein extract (insect hydrolysate at 0%, 5%, 10% and 15%). ¹H-NMR profiling was used to assess metabolites in experimental diets and in fish plasma, liver and muscle. A significant dose-dependent increase in growth and feed efficiency with increasing insect extract amounts was observed. The incremental incorporation of the insect extract in diet had a significant and progressive impact on the profile of dietary soluble compounds and trout metabolome. The metabolites modulated by dietary insect extracts in plasma and tissues were involved in protein and energy metabolism. This was associated with the efficient metabolic use of dietary free amino acids toward protein synthesis through the concomitant supply of balanced free amino acids and energy substrates in muscle. The findings provide new insights into how the dietary food metabolome affects fish metabolism.

Compositional identification and authentication of Chinese honeys by 1H NMR combined with multivariate analysis

Honey authentication has been becoming more and more important and necessary to the honey producers, the consumers and the market regulatory authority due to its favorite organoleptic and healthy properties, high value and increasing export but prevalent falsification practice for economic motivation in China and the potential health risk of adulterated honey. In this study, we obtained the spectral profiles of 90 authentic and 75 adulterated Chinese honey samples by means of high resolution nuclear magnetic resonance (NMR) spectroscopy, and 65 kinds of major and minor components in honey were identified and quantified from their NMR spectra. Combining with the multivariate statistical analyses including principal component analysis (PCA), linear discriminant analysis (LDA), and orthogonal partial least squared-discriminant analysis (OPLS-DA), the discrimination models were successfully established to identify the adulterated honeys from the authentic ones with an accurate rate of 97.6%. Furthermore, the corresponding volcano plot was used to screen out 8 components including proline, xylobiose, uridine, β-glucose, melezitose, turanose, lysine and an unknown component, which are responsible for the differentiation between the authentic and adulterated honeys and will help to control Chinese domestic honey market.

High-resolution pure shift NMR spectroscopy offers better metabolite discrimination in food quality analysis

PSYCHE homonuclear decoupling, a prominent pure shift NMR method, is successfully applied to adulteration discrimination of honey and geographical originality identification of tea. Effects of homonuclear couplings are efficiently suppressed, producing resolution-enhanced spectra. The pair wise honey and tea samples are well separated in OPLS-DA models with high predictability. Due to the well-resolved and accurate assignment of singlet resonances after decoupling, PSYCHE is advantageous in the identification of differential components and accurate quantification of compound concentrations presented by enhanced volcano and Beeswarm plots of honey samples, while the analysis of NOESY is easily interfered by overlapped resonances, which is further proved by the STOCSY analysis, displaying the spectral stability and reproducibility. Experimental results show that PSYCHE can improve the spectral resolution of natural complex products such as honey and tea and be combined with multivariate statistical analysis and serve as a supplementary technique to the standard methods, especially for samples systems composed by a few high-content compounds.

Metabolic Effect of Dietary Taurine Supplementation on Grouper (Epinephelus coioides): A 1H-NMR-Based Metabolomics Study

Taurine is an indispensable amino acid for many fish species and taurine supplementation is needed when plant-based diets are used as the primary protein source for these species. However, there is limited information available to understand the physiological or metabolic effects of taurine on fish. In this study, ¹H nuclear magnetic resonance (NMR)-based metabolomic analysis was conducted to identify the metabolic profile change in the fish intestine with the aim to assess the effect of dietary taurine supplementation on the physiological and metabolomic variation of fish, and reveal the possible mechanism of taurine's metabolic effect. Grouper (Epinephelus coioides) were divided into four groups and fed diets containing 0.0%, 0.5%, 1.0%, and 1.5% taurine supplementation for 84 days. After extraction using aqueous and organic solvents, 25 significant taurine-induced metabolic changes were identified. These metabolic changes in grouper intestine were characterized by differences in carbohydrate, amino acid, lipid and nucleotide. The results reflected both the physiological state and growth of the fish, and indicated that taurine supplementation significantly affects the metabolome of fish, improves energy utilization and amino acid uptake, promotes protein, lipid and purine synthesis, and accelerates fish growth.

Taurine Promotes Milk Synthesis via the GPR87-PI3K-SETD1A Signaling in BMECs

Taurine, a β-aminosulfonic acid, exerts many cellular physiological functions. It is still unknown whether taurine can regulate milk synthesis in the mammary gland. Therefore, in this study we investigated the effects and mechanism of taurine on milk synthesis in mammary epithelial cells (MECs). Bovine MECs (BMECs) cultured in FBS-free OPTI-MEMImedium were treated with taurine (0, 0.08, 0.16, 0.24, 0.32, and 0.4 mM). Taurine treatment led to increased milk protein and fat synthesis, mTOR phosphorylation, and SREBP-1c protein expression, in a dose-dependent manner, with an apparent maximum at 0.24 mM. Gene function study approaches revealed that the GPR87-PI3K-SETD1A signaling was required for taurine to increase the mTOR and SREBP-1c mRNA levels. Taurine stimulated GPR87 expression and cell membrane localization in a dose dependent manner, suggesting a sensing mechanism of GPR87 to extracellular taurine. Collectively, these data demonstrate that taurine promotes milk synthesis via the GPR87-PI3K-SETD1A signaling.

Odorants in Fish Feeds: A Potential Source of Malodors in Aquaculture

Although the microbiota is considered to be the primary source of off-flavors in farmed fish, there is a lack of information about the possible contribution of feeds to fish malodor. For this reason, the current study was designed to perform comprehensive sensory and chemo-analytical characterization of fish feed constituents that can impact the quality of farmed fish, and to determine whether feeds cause malodor accumulation in fish. To this aim, odorants in four commercial fish feeds were extracted using solvent assisted flavor evaporation (SAFE) and characterized by comparative aroma extract dilution analysis (cAEDA) and multi-dimensional gas chromatography-mass spectrometry/olfactometry (MD-GC-MS/O). The odorants in the fish feed samples were correlated with their respective sensory and fatty acid profiles. The cAEDA studies revealed the presence of 81 odorants of which 55 compounds were common to all the samples. Most of these odorants are identified here for the first time in fish feeds, and include skatole, indole, (E,Z,Z)-2,4,7-tridecatrienal, 4-ethyloctanoic acid, and cresols. Additionally, geosmin and 3-isopropyl-2-methoxypyrazine, known for their contribution to fish taint, and other cyanobacterial by-products, dimethyldisulfide and dimethyltrisulfide, were identified in feed samples. The results suggest that fish feed may contribute to fish malodor. Most of these off-flavors were linked to lipid source (fish oil or plant/lard alternatives), unsaturated fatty acids contents, and protein type (plant-based or fishmeal-based sources) in the feed.