Long-term feeding a plant-based diet devoid of marine ingredients strongly affects certain key metabolic enzymes in the rainbow trout liver

Screening and Identification of a Strain with Protease and Phytase Activities and Its Application in Soybean Meal Fermentation

The aims of the study were to degrade the anti-nutritional factors (ANFs) such as phytic acid, glycinin, and β-conglycinin and improve the values of soybean meal (SBM). Firstly, in this study, a strain PY-4B which exhibited the best enzymatic activities of protease (403.3 ± 17.8 U/mL) and phytase (62.9 ± 2.9 U/mL) was isolated and screened among the isolates. Based on the analysis of physiological and biochemical characteristics and 16S rDNA sequence, the strain PY-4B was identified and named as Pseudomonas PY-4B. Next, Pseudomonas PY-4B was applied to fermentation of SBM. The results showed that the contents of glycinin and β-conglycinin were decreased by 57-63%, and the phytic acid was remarkably degraded by 62.5% due to the fermentation of SBM by Pseudomonas PY-4B. The degradation of glycinin and β-conglycinin resulted in increase of contents of water-soluble proteins and amino acids in fermented SBM. Moreover, Pseudomonas PY-4B exhibited no hemolytic activity and slight inhibitory effect on the growth of pathogen Staphylococcus aureus and the wide range of pH tolerance (3 to 9). In summary, our study indicates that isolated strain Pseudomonas PY-4B is a safe and applicable strain and has the ability to effectively degrade the ANFs (phytic acid, glycinin, and β-conglycinin) in SBM by fermentation.

Soluble non-starch polysaccharides in fish feed: implications for fish metabolism

Because of their unique glycosidic bond structure, non-starch polysaccharides (NSP) are difficult for the stomach to break down. NSP can be classified as insoluble NSP (iNSP, fiber, lignin, etc.) and soluble NSP (sNSP, oligosaccharides, β-glucan, pectin, fermentable fiber, inulin, plant-derived polysaccharides, etc.). sNSP is viscous, fermentable, and soluble. Gut microbiota may catabolize sNSP, which can then control fish lipid, glucose, and protein metabolism and impact development rates. This review examined the most recent studies on the impacts of various forms of sNSP on the nutritional metabolism of various fish in order to comprehend the effects of sNSP on fish. According to certain investigations, sNSP can enhance fish development, boost the activity of digestive enzymes, reduce blood sugar and cholesterol, enhance the colonization of good gut flora, and modify fish nutrition metabolism. In-depth research on the mechanism of action is also lacking in most studies on the effects of sNSP on fish metabolism. It is necessary to have a deeper comprehension of the underlying processes by which sNSP induce host metabolism. This is crucial to address the main issue of the sensible use of carbohydrates in fish feed.

Exploring the effects of dietary inulin in rainbow trout fed a high-starch, 100% plant-based diet

BACKGROUND

High dietary carbohydrates can spare protein in rainbow trout (Oncorhynchus mykiss) but may affect growth and health. Inulin, a prebiotic, could have nutritional and metabolic effects, along with anti-inflammatory properties in teleosts, improving growth and welfare. We tested this hypothesis in rainbow trout by feeding them a 100% plant-based diet, which is a viable alternative to fishmeal and fish oil in aquaculture feeds. In a two-factor design, we examined the impact of inulin (2%) as well as the variation in the carbohydrates (CHO)/plant protein ratio on rainbow trout. We assessed the influence of these factors on zootechnical parameters, plasma metabolites, gut microbiota, production of short-chain fatty acids and lactic acid, as well as the expression of free-fatty acid receptor genes in the mid-intestine, intermediary liver metabolism, and immune markers in a 12-week feeding trial.

RESULTS

The use of 2% inulin did not significantly change the fish intestinal microbiota, but interestingly, the high CHO/protein ratio group showed a change in intestinal microbiota and in particular the beta diversity, with 21 bacterial genera affected, including Ralstonia, Bacillus, and 11 lactic-acid producing bacteria. There were higher levels of butyric, and valeric acid in groups fed with high CHO/protein diet but not with inulin. The high CHO/protein group showed a decrease in the expression of pro-inflammatory cytokines (il1b, il8, and tnfa) in liver and a lower expression of the genes coding for tight-junction proteins in mid-intestine (tjp1a and tjp3). However, the 2% inulin did not modify the expression of plasma immune markers. Finally, inulin induced a negative effect on rainbow trout growth performance irrespective of the dietary carbohydrates.

CONCLUSIONS

With a 100% plant-based diet, inclusion of high levels of carbohydrates could be a promising way for fish nutrition in aquaculture through a protein sparing effect whereas the supplementation of 2% inulin does not appear to improve the use of CHO when combined with a 100% plant-based diet.

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.

Interaction between genetics and inulin affects host metabolism in rainbow trout fed a sustainable all plant-based diet

Inulin affects nutrition and metabolism in many animals. Although inulin is widely used in the diet of teleosts, its mechanism of action is unknown. Here, we investigated the effect of inulin (2 %) on the intestinal microbiome and metabolism in rainbow trout (Oncorhynchus mykiss) selected for growth and survival when fed a 100 % plant-based diet (suave) and a control line (temoin). Metabolic responses to the two factors (line and inulin) in liver, intestine, muscle and adipose were tissue-specific, with line and interaction between the two factors influencing overall expression in liver. In the intestine, inulin and line and in muscle, line influenced the expression of metabolic genes. Microbiota between the mucus and digestive contents was significantly different, with genera from Proteobacteria being more abundant in the mucus, whereas genera from the Firmicutes and Planctomycetes being more abundant in contents. Effect of inulin and interaction between factors on the microbiome was evident in contents. The significant taxa of control and inulin-fed groups differed greatly with Streptococcus and Weissella being significantly abundant in the inulin-fed group. There was a general trend showing higher levels of all SCFA in temoin group with propionic acid levels being significantly higher. An operational taxonomic unit (OTU) belonging to the Ruminococcaceae was significantly abundant in suave. The tissue-specific correlations between OTU and gene expression may indicate the link between microbiome and metabolism. Together, these results suggest that line and inulin impact the gene expression in a tissue-specific manner, possibly driven by specific OTUs enriched in inulin-fed groups and suave.

Sources of protein diet differentially stimulate the gut and water microbiota under freshwater crayfish, marron (Cherax cainii, Austin 2002) culture

To reduce the reliance on fishmeal (FM), other protein sources have been evaluated on cultured animals. In a 60-days feeding trial, marrons (Cherax cainii) were fed a FM diet and five test diets containing 100% of plant-based protein sources such as soybean, lupin and valorised animal-based proteins such as poultry-by-product, black soldier fly and tuna hydrolysate. At the end of the trial, DNA samples from marron gut and rearing water were investigated through DNA-based 16S rRNA gene sequencing. Plant-based diets increased abundance for Aeromonas, Flavobacterium and Vogesella, whereas animal and insect proteins influenced diverse bacterial groups in the gut linked to various metabolic activities. Insect meal in the water favoured the growth of Firmicutes and lactic acid bacteria, beneficial for the marron health. Aeromonas richness in the gut and reared water signified the ubiquitous nature of the genus in the environment. The higher bacterial diversity in the gut and water with PBP and BSF was further supported by qPCR quantification of the bacterial single-copy gene, rpoB. The overall results suggested that PBP and BSF can exhibit positive and influential effects on the gut and water microbial communities, hence can be used as sustainable ingredients for the crayfish aquaculture.

Detection and Modulation of Olfactory Sensing Receptors in Carnivorous Rainbow Trout (Oncorhynchus mykiss) Fed from First Feeding with Plant-Based Diet

Sense of smell is mediated by diverse families of olfactory sensing receptors, conveying important dietary information, fundamental for growth and survival. The aim of this study was to elucidate the role of the sensory olfactory pathways in the regulation of feeding behavior of carnivorous rainbow trout (RT, Oncorhynchus mykiss), from first feeding until 8 months. Compared to a commercial diet, RT fed with a total plant-based diet showed drastically altered growth performance associated with feed intake from an early stage. Exhaustive examination of an RT genome database identified three vomeronasal type 1 receptor-like (ORA), 10 vomeronasal type 2 receptor-like (OLFC) and 14 main olfactory receptor (MOR) genes, all highly expressed in sensory organs, indicating their potential functionality. Gene expression after feeding demonstrated the importance in olfactory sensing perception of some OLFC (olfcg6) and MOR (mor103, -107, -112, -113, -133) receptor family genes in RT. The gene ora1a showed evidence of involvement in olfactory sensing perception for fish fed with a commercial-like diet, while ora5b, mor118, mor124 and olfch1 showed evidence of involvement in fish fed with a plant-based diet. Results indicated an impact of a plant-based diet on the regulation of olfactory sensing pathways as well as influence on monoaminergic neurotransmission in brain areas related to olfactory-driven behaviors. The overall findings suggest that feeding behavior is mediated through olfactory sensing detection and olfactory-driven behavior pathways in RT.

Soybean protein concentrate as a protein source for totoaba (Totoaba macdonaldi) juveniles: Effect on intermediary metabolism and liver histological organization

This study aimed to investigate the effects of replacing fish meal (FM) with soybean protein concentrates (SPC) on the intermediary metabolism and health of Totoaba macdonaldi juveniles. Fish (initial weight 50 ± 1 g) were fed for 60 days with eight diets: a reference diet (RD) and seven experimental diets where FM was replaced gradually with 15 to 100% SPC (SPC15, SPC30, SPC45, SPC60, SPC75, SPC90, and SPC100, respectively). Hexokinase (HK), glucokinase (GK), and alanine aminotransferase (ALT) enzyme activities showed highly significant differences (p < 0.01) between fish fed RD (0% SPC) compared to fish fed the diets with 60, 75, 90, and 100% SPC. The ALT enzyme shows a highly significant (p < 0.01) decrease in activity for fish fed 75, 90, and 100% SPC inclusions compared to fish fed the RD. The aspartate aminotransferase AST/ALT ratio showed a significant increase in activity for fish fed 100% soybean compared only with fish fed the control diet. The histological organization of the liver in totoaba juveniles fed RD, SPC15, SPC30 and SPC45 diets were similar. Totoaba fed with SPC90 and SPC100 showed histological alterations in hepatic and pancreatic parenchyma. Overall, according to the findings in this study, 45% of dietary FM could be replaced by SPC without causing adverse changes in metabolism, histological organization of liver, and health of juveniles of totoaba when cultured for 60 days. However, levels greater than 60% of SPC could compromise the health status of fish.

Asymmetric expression of homoeologous genes contributes to dietary adaption of an allodiploid hybrid fish derived from Megalobrama amblycephala (♀) × Culter alburnus (♂)

BACKGROUND

Hybridization, which can quickly merge two or more divergent genomes and form new allopolyploids, is an important technique in fish genetic breeding. However, the merged subgenomes must adjust and coexist with one another in a single nucleus, which may cause subgenome interaction and dominance at the gene expression level and has been observed in some allopolyploid plants. In our previous studies, newly formed allodiploid hybrid fish derived from herbivorous Megalobrama amblycephala (♀) × carnivorous Culter alburnus (♂) had herbivorous characteristic. It is thus interesting to further characterize whether the subgenome interaction and dominance derive dietary adaptation of this hybrid fish.

RESULTS

Differential expression, homoeolog expression silencing and bias were investigated in the hybrid fish after 70 days of adaptation to carnivorous and herbivorous diets. A total of 2.65 × 108 clean reads (74.06 Gb) from the liver and intestinal transcriptomes were mapped to the two parent genomes based on specific SNPs. A total of 2538 and 4385 differentially expressed homoeologous genes (DEHs) were identified in the liver and intestinal tissues between the two groups of fish, respectively, and these DEHs were highly enriched in fat digestion and carbon metabolism, amino acid metabolism and steroid biosynthesis. Furthermore, subgenome dominance were observed in tissues, with paternal subgenome was more dominant than maternal subgenome. Moreover, subgenome expression dominance controlled functional pathways in metabolism, disease, cellular processes, environment and genetic information processing during the two dietary adaptation processes. In addition, few but sturdy villi in the intestine, significant fat accumulation and a higher concentration of malondialdehyde in the liver were observed in fish fed carnivorous diet compared with fish fed herbivorous diet.

CONCLUSIONS

Our results indicated that diet drives phenotypic and genetic variation, and the asymmetric expression of homoeologous genes (including differential expression, expression silencing and bias) may play key roles in dietary adaptation of hybrid fish. Subgenome expression dominance may contribute to uncovering the mechanistic basis of heterosis and also provide perspectives for fish genetic breeding and application.

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.

Intestinal Transcriptome Analysis Highlights Key Differentially Expressed Genes Involved in Nutrient Metabolism and Digestion in Yellowtail Kingfish (Seriola lalandi) Fed Terrestrial Animal and Plant Proteins

This study investigated the effects of dietary terrestrial animal and plant proteins on the intestinal transcriptomes of yellowtail kingfish (YTK), Seriola lalandi, an ecologically and economically important marine species in Australia. Five diets containing fish meal (FM), poultry by-product meal (PBM), blood meal (BLM), faba bean meal (FBM) and corn gluten meal (CGM) were formulated and fed over a period of 4 weeks. The Illumina RNA-sequencing (RNA-Seq) results identified a suite of differentially expressed genes involved in nutrient metabolism and protein digestion pathways, reinforced by quantitative polymerase chain reaction (qPCR) results. These findings provide molecular support to the notion that PBM and FBM are useful raw materials in commercial diets for YTK. Using the same evidence, we have demonstrated that BLM and CGM may be less useful and their incorporation into commercial aquafeeds for this species should be done cautiously. The differentially expressed genes showed a subtle difference and high correlation with apparent nutrient digestibility of raw materials. Further, our results indicate that transcriptome profiling provides a useful tool to evaluate alternative protein sources for use in aquaculture feeds.

Fermented Soybean Meal Increases Lactic Acid Bacteria in Gut Microbiota of Atlantic Salmon (Salmo salar)

The main goal of the present study was to address the effect of feeding fermented soybean meal-based diet to Atlantic salmon on gut microbiota. Further, expression of genes of interest, including cathelicidin antimicrobial peptide (cath), mucin 2 (muc2), aquaporin (aqp8ab), and proliferating cell nuclear antigen (pcna), in proximal intestine of fish fed either experimental diet was analyzed. Three experimental diets, including a control fishmeal (30% FM), soybean meal (30% SBM), or fermented soybean meal diet (30% FSBM) were randomly assigned to triplicate tanks during a 50-day trial. The PCR-TTGE showed microbiota composition was influenced by experimental diets. Bands corresponding to genus Lactobacillus and Pediococcus were characteristic in fish fed the FSBM-based diet. On the other hand, bands corresponding to Isoptericola, Cellulomonas, and Clostridium sensu stricto were only observed in fish FM-based diet, while Acinetobacter and Altererythrobacter were detected in fish fed SBM-based diet. The expression of muc2 and aqp8ab were significantly greater in fish fed the FSBM-based diet compared with the control group. Our results suggest feeding FSBM to Atlantic salmon may (1) boost health and growth physiology in fish by promoting intestinal lactic acid bacteria growth, having a prebiotic-like effect, (2) promote proximal intestine health by increasing mucin production, and (3) boost intestinal trans-cellular uptake of water. Further research to better understands the effects of bioactive compounds derived from the fermentation process of plant feedstuff on gut microbiota and the effects on health and growth in fish is required.

Influence of vegetable diets on physiological and immune responses to thermal stress in Senegalese sole (Solea senegalensis)

The substitution of fish resources as ingredients for aquafeeds by those based on vegetable sources is needed to ensure aquaculture sustainability in the future. It is known that Senegalese sole (Solea senegalensis) accepts high dietary content of plant ingredients without altering growth or flesh quality parameters. However, scarce information is available regarding the long-term impact of vegetable diets (combining the inclusion of both vegetable protein and oils) on the stress response and immunity of this fish species. This study aims to evaluate the concomitant effect of the extended use of vegetable protein-based diets with fish oil (FO) replacement (0, 50 or 100%) by vegetable oils (VO), on the response to acute (10 min) or prolonged (4 days) stress, induced by thermal shock. Plasma levels of cortisol, glucose and lactate as well as hepatic levels of glucose, glycogen and lactate were evaluated as primary and secondary responses to stress, 6 and 18 months after feeding the experimental diets (6 and 18 MAF). The brain monoaminergic activity in telencephalon and hypothalamus, and non-specific immune parameters were also evaluated. As expected, thermal shock induced an increase in values of plasma parameters related to stress, which was more evident in acute than in prolonged stress. Stress also affected lactate levels in the liver and the values of the alternative complement pathway-ACH50 in the plasma. Dietary substitution of FO induced an effect per se on some parameters such as decreased hepatic glucose and glycogen levels and peroxidase activity in plasma as well enhanced serotonergic activity in brain of non-stressed fish. The results obtained in some parameters indicate that there is an interaction between the use of vegetable diets with the physiological response to thermal stress, as is the case of the hepatic lactate, serotonergic neurotransmission in brain, and the activity of ACH50 in plasma. These results suggest that the inclusion of VO in plant protein based diets point to a slightly inhibited stress response, more evident for an acute than a prolonged stress.