Dietary yeast hydrolysate and brewer's yeast supplementation could enhance growth performance, innate immunity capacity and ammonia nitrogen stress resistance ability of Pacific white shrimp (Litopenaeus vannamei)

Toxicity of three microcystin variants on the histology, physiological and metabolism of hepatopancreas and intestinal microbiota of Litopenaeus vannamei

Microcystins (MCs) are prevalent harmful contaminants within shrimp aquaculture systems, exhibiting a diverse array of variants. Gut microbiota can engage in mutual interactions with the host through the gut-liver axis. In this study, the shrimp Litopenaeus vannamei were subjected to three different variants of MCs (LR, YR, RR) at a concentration of 1 μg/L each, and elucidated the alterations in both intestinal microbiota and hepatopancreas physiological homeostasis. The results showed that all three variants of MCs prompted histological alterations in the hepatopancreas, induced elevated levels of oxidative stress biomarkers (H2O2, T-SOD, and CAT), disturbed the transcription levels of immune-related genes (Crus, ALF, and Lys), along with an increase in apoptotic genes (Casp-3 and P53). Furthermore, the metabolic profiles of the hepatopancreas were perturbed, particularly in amino acid metabolism such as "lysine degradation" and "β-alanine metabolism"; the mTOR and FoxO signaling were also influenced, encompassing alterations in the transcription levels of related genes. Additionally, the alterations were observed in the intestinal microbiota's diversity and composition, particularly potential beneficial bacteria (Alloprevotella, Bacteroides, Collinsella, Faecalibacterium, and Prevotellaceae UCG-001), which exhibited a positive correlation with the metabolite berberine. These findings reveal that the three MCs variants can impact the health of the shrimp by interfering with the homeostasis of intestinal microbial and hepatopancreas physiology.

Dietary Bacillus velezensis T23 fermented products supplementation improves growth, hepatopancreas and intestine health of Litopenaeus vannamei

This study aimed to elucidate the effects of dietary fermented products of Bacillus velezensis T23 on the growth, immune response and gut microbiota in Pacific white shrimp (Litopenaeus vannamei). Shrimp were fed with diets containing fermentation products of B. velezensis T23 at levels of (0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 g/kg) for 4 weeks, to assess the influence on shrimp growth. The results showed that 0.3 and 0.4 g/kg T23 supplementation improved shrimp growth and feed utilization. Based on these results we selected these three diets (Control, 0.3T23 and 0.4T23) to assess the effect on immune response and gut microbiota of shrimp. Compared with the control, the 0.3T23 and 0.4T23 groups enhanced lipase and α-amylase activities in the gut significantly. Moreover, the 0.4T23 group decreased TAG and MDA levels in hepatopancreas, ALT and AST levels of serum significantly (P < 0.05). In hepatopancreas, CAT and SOD activities were improved observably and the MDA content was reduced markedly in both T23 groups. The expressions of antimicrobial related genes, Cru and peroxinectin in the 0.3T23 group, and proPO and peroxinectin in the 0.4T23 group were up-regulated remarkably (P < 0.05). Moreover, hepatopancreas of shrimp fed with a diet amended with T23 showed a significant down-regulated expression of nf-kb and tnf-α genes, while expressions of tgf-β was considerably up-regulated. Furthermore, serum LPS and LBP contents were reduced markedly in T23 groups. Intestinal SOD and CAT were noteworthy higher in T23 groups (P < 0.05). In the intestine of shrimp fed on the diet enriched with T23 the expression of nf-κb and tnf-α exhibited markedly down-regulated, whereas hif1α was up-regulated (P < 0.05). Besides, in the intestine of shrimp grouped under T23, Cru and peroxinectin genes were markedly up-regulated (P < 0.05). Dietary 0.3 g/kg T23 also upregulated the ratio of Rhodobacteraceae to Vibrionaceae in the gut of the shrimp. Taken together, the inclusion of B. velezensis T23 in the diet of shrimp enhanced the growth and feed utilization, enhanced hepatopancreas and intestine health.

Fish Responses to Alternative Feeding Ingredients under Abiotic Chronic Stress

Aquaculture has become one of the most attractive food production activities as it provides high-quality protein for the growing human population. However, the abiotic chronic stress of fish in intensive fish farming leads to a detrimental condition that affects their health and somatic growth, comprising productive performance. This work aims to comprehensively review the impact of alternative and novel dietary protein sources on fish somatic growth, metabolism, and antioxidative capacity under environmental/abiotic stressors. The documental research indicates that ingredients from rendered animal by-products, insects, bacteria as single-cell proteins, and fungal organisms (e.g., yeast, filamentous fungus, and mushrooms) benefit fish health and performance. A set of responses allows fish growth, health, and survival to remain unaffected by feeding with alternative ingredients during chronic environmental stress. Those ingredients stimulate the production of enzymes such as catalase, glutathione peroxidase, and selenoproteins that counteract ROS effects. In addition, the humoral immune system promotes immunoglobulin production (IgM) and cortisol plasmatic reduction. Further investigation must be carried out to establish the specific effect by species. Additionally, the mixture and the pre-treatment of ingredients such as hydrolysates, solid fermentations, and metabolite extraction potentialize the beneficial effects of diets in chronically stressed fish.

Effects of Dietary β-Glucan Feeding Strategy on the Growth, Physiological Response, and Gut Microbiota of Pacific White Shrimp, Litopenaeus vannamei, under Low Salinity

An eight-week feeding trial was conducted to investigate the effects of a dietary β-glucan application strategy on the growth performance, physiological response, and gut microbiota of Pacific white shrimp (Litopenaeus vannamei) (0.49 ± 0.17 g) under low salinity. Six feeding strategies were established, including a continuous β-glucan-free diet group (control), a continuously fed group with a 0.1% β-glucan diet (T1), and groups with the following intermittent feeding patterns: 1 day of β-glucan diet and 6 days of β-glucan-free diet (T2), 2 days of β-glucan diet and 5 days of β-glucan-free diet (T3), 3 days of β-glucan diet and 4 days of β-glucan-free diet (T4), and 4 days of β-glucan diet and 3 days of β-glucan-free diet (T5) each week. No significant differences in growth performance among all the groups were found, although the condition factor was significantly higher in the T3 group than in the T1 and T5 groups (p < 0.05). The T-AOC and GPX activities were significantly lower in the T3 group than in the control group (p < 0.05). The MDA content was also significantly lower in the T2 group than in the T3 and T4 groups (p < 0.05). Additionally, the mRNA expression of the Pen3a gene was significantly upregulated in the hepatopancreas of the T4 group compared to the control and T5 groups (p < 0.05), and the Toll gene was also significantly upregulated in the T3 group compared to the T1 and T2 groups (p < 0.05). Dietary β-glucan induced changes in the alpha diversity and composition of the gut microbiota in different feeding strategies. The beta diversity of the gut microbiota in the T2 group was significantly different from that in the control group. The results of a KEGG analysis showed that gut function in the carbohydrate metabolism, immune system, and environmental adaptation pathways was significantly enhanced in the T3 group. These findings provide evidence that the intermittent feeding strategy of β-glucan could alleviate immune fatigue, impact antioxidant ability, and change gut microbiota composition of L. vannamei under low salinity.

Effects of dietary supplementation of Bacillus subtilis DSM 32315 on growth, immune response and acute ammonia stress tolerance of Nile tilapia (Oreochromis niloticus) fed with high or low protein diets

Aquatic animals have benefited from Bacillus subtilis-based probiotics over the past few decades. This study evaluated the effects of B. subtilis DSM 32315 probiotics as a feed additive on growth, immune response and resistance to acute ammonia challenge in Nile tilapia. Specifically, four supplemental levels (0%, 0.1%, 0.2%, and 0.3%) of B. subtilis probiotics were tested under two dietary protein levels (32% and 28%). Five replicate tanks were randomly allotted to each dietary treatment, with each tank containing 30 Nile tilapia. After 8 weeks of feeding, Nile tilapia in each tank were exposed to 43.61 mg/L of total ammonia nitrogen for 48 h. The results revealed that reducing protein levels from 32% to 28% did not affect growth performance or antioxidant capacity. However, the low protein diet tended to induce an inflammatory effect shown by increased expressions of TGF-β and IFN-γ genes (P < 0.05) in the liver. The impact was alleviated by the probiotic supplementation. Compared with the non-supplemented group, 0.1% probiotic supplementation remarkably increased plasma lysozyme activity, total antioxidant capacity and complement C3 and interleukin-10 mRNA levels (P < 0.05) in the 28% protein diet, while higher supplementation of probiotics (0.3%) was shown to be beneficial for the high protein diet (32%). In both the dietary protein levels, 0.1% supplementation of probiotics promoted the antioxidant capacity of Nile tilapia before exposure to ammonia stress but higher probiotic supplementation (0.3%) proved to be necessary under ammonia stress as evidenced by higher fish survival rate. Results exhibited that supplementation with B. subtilis probiotics had a better effect on the intestinal morphology (villi height and width) regardless of protein levels. In conclusion, dietary supplementation of B. subtilis DSM 32315 probiotics at 0.1% in the low protein diet and up to 0.3% in the high protein diet showed beneficial effects on the growth, immunity, and antioxidant capacity of Nile tilapia. Under ammonia stress conditions, the higher supplementation of B. subtilis DSM 32315 probiotics at 0.3% improves stress tolerance of Nile tilapia despite the two dietary protein levels (32%; 28%).

The Efficacy of Yeast Supplementation on Monogastric Animal Performance-A Short Review

Due to a continual growth in the world's population and the prohibition of antibiotics in animal production, the livestock industry faces significant challenges in the global demand for meat, eggs, and dairy products. The growing demand for organic products and the prohibition on antibiotic growth promoters (AGPs) have compelled animal nutrition experts to search for natural substitutes that include medical plants and beneficial microorganisms. Natural feed additives like probiotics are found to be more effective than AGPs in reducing the load of harmful intestinal pathogens. One of the probiotics that has generated considerable interest since ancient times is yeast. Yeast is used as a supplement in animal feeds due to its relatively high protein, amino acid, energy, and micronutrient content. Yeast byproducts such as yeast cells and cell walls contain nutraceutical compounds (i.e., β-glucans, mannooligosaccharides, and nucleotides) and have been shown to improve animal growth performance and health. Though the application of yeast supplements has been reviewed to date, only a scarce amount of information exists on the yeast-derived products in non-ruminant nutrition. Additionally, it is difficult for nutritionists to differentiate the characteristics, composition, and optimal feeding among the diverse number of yeast-containing products. Due to the increasing popularity of using yeast-based products in animal feeds, the development of analytical approaches to estimate yeast and its components in these products is greatly needed. Thus, in this review, we intend to provide current knowledge of different categories of commercially available yeast and yeast-derived additives, along with their role in improving animal growth performance and health, their proposed mechanisms of action, and the challenges of quantifying yeast content and biologically active components.

Effect of fed dietary yeast (Rhodotorula paludigena CM33) on shrimp growth, gene expression, intestinal microbial, disease resistance, and meat composition of Litopenaeus vannamei

Yeast is a health-promoting and bio-therapeutic probiotic that is commonly used in aquaculture. Rhodotorula paludigena CM33 can accumulate amounts of intracellular carotenoids and lipid, which are regarded as nutritionally beneficial compounds in various aspects. The aim of this study was to evaluate the impact of different levels of R. paludigena CM33 (RD) incorporated in a dietary composition at 0% (control), 1% (1% RD), 2% (2% RD), and 5% (5% RD) on the growth of shrimp (Litopenaeus vannamei), their immune-related gene expression, intestinal health, resistance to Vibrio parahaemolyticus (VPAHPND) infection, and meat composition. The results showed significant improvements in the specific growth rate, weight gain, and survival of shrimp fed with 1% RD, 2% RD, and 5% RD, which were higher than the control group after 4 weeks of administration. The administration of 5% RD group resulted in a decrease in cumulative mortality upon VPAHPND challenge when compared to the control group. Furthermore, the expression levels of immune-responsive genes, including proPO system (prophenoloxidase-2: PO2), antioxidant enzyme (superoxide dismutase: SOD, glutathione peroxidase: GPX, and catalase: CAT), JAK/STAT pathway (signal transducer and activator of transcription: STAT, gamma interferon inducible lysosomal thiol reductase: GILT), IMD pathway (inhibitor of nuclear factor kappa-B kinase subunit beta and epsilon: IKKb and IKKe), and Toll pathway (Lysozyme) genes, were up-regulated in the 5% RD group. In the context of microbiota, microbiome analysis revealed that the main phyla in shrimp intestines were Proteobacteria, Firmicutes, Bacteroidota, Campilobacterota, Actinobacteriota, and Verrucomicrobiota. At the genus level, Vibrio was found to be reduced in the 5% RD group, whereas the abundance of potentially beneficial bacteria Bifidobacterium was increased. The 5% RD group showed a significant increase in the levels of crude protein and crude lipid, both of which are essential nutritious components. Our results show the capability of R. paludigena CM33 as a probiotic supplement in shrimp feed in improving growth, antimicrobial responses against VPAHPND, and meat quality by increasing protein and lipid content in shrimp.

Protective effects of yeast extract against alcohol-induced liver injury in rats

Oxidative stress, inflammatory response, and gut-liver axis dysbiosis have been suggested as the primarily involved in the pathogenesis of alcoholic liver injury. Previous research established that yeast extract (YE) has antioxidant, immune-boosting or microbiota-regulating properties. However, there is currently lack of information regarding the efficacy of YE on alcoholic liver injury. This study seeks to obtain data that will help to address this research gap using a Wistar male rat experimental model. Histologic and biochemical analysis results showed that the groups treated with both low-dose yeast extract (YEL) and high-dose yeast extract (YEH) had lower degrees of alcohol-induced liver injury. The abundance of Peptococcus and Ruminococcus reduced in the low-dose yeast extract (YEL) group, while that of Peptococcus, Romboutsia, Parasutterella, and Faecalibaculum reduced in the high-dose (YEH) group. Furthermore, Spearman analysis showed that the gut microbes were significantly associated with several liver-related indicators. For the analysis of differential metabolites and enriched pathways in the YEL group, the abundance of lysophosphatidylcholine (16:0/0:0) significantly increased, and then the levels of histamine, adenosine and 5' -adenine nucleotide were remarkedly elevated in the YEH group. These findings suggest that both high and low doses of YE can have different protective effects on liver injury in alcoholic liver disease (ALD) rats, in addition to improving gut microbiota disorder. Besides, high-dose YE has been found to be more effective than low-dose YE in metabolic regulation, as well as in dealing with oxidative stress and inflammatory responses.

Effects of yeast hydrolysate supplementation in low-fish meal diets for pikeperch

Plant proteins have been increasingly used as sustainable substitutes for fish meal (FM) in aquafeeds; however, their high inclusion level compromises fish performance. The objective of this study was to examine whether yeast hydrolysate (YH) supplementation can improve the utilisation of high soybean meal (SM) diet and ameliorate its potential deteriorating impacts in pikeperch (Sander lucioperca). A basal diet was formulated using 44% FM, and four additional diets were produced by replacing 30 or 60% of FM with SM with or without the addition of 2% YH (FM, SM30, SM60, SM30 + YH, and SM60 + YH diets). Each diet was fed to three groups of fish (35.3 ± 0.10 g, 150 fish per group) to visual satiety four times daily for 70 days. Fish growth was not impacted by FM replacement level or YH application. However, SM60 group exhibited markedly higher feed conversion ratio and lower survival rate than those fed the FM- and YH-supplemented diets (P < 0.05). The highest and the lowest protein efficiency ratio values were obtained for the SM30 + YH and SM60 groups, respectively. Whole-body lipid content decreased in SM60 and SM60 + YH groups, and muscle lipid decreased in all the replacement groups. Serum triglyceride and glucose concentrations tended to decrease as FM replacement level increased. The highest alanine aminotransferase, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) activities were detected in the SM60 group, and YH addition significantly decreased the AST and LDH activities. Serum lysozyme activity decreased in SM30, SM60 and SM60 + YH groups. Serum myeloperoxidase and antiprotease activities decreased in SM60 group, and YH supplementation improved their activities. No effects of diets were observed on serum antioxidant parameters such as catalase activity and malondialdehyde concentration, and gut morphological indices. Number of goblet cells in midgut decreased by increasing the SM inclusion level and a slight improvement was observed by YH application. These findings suggest that YH supplementation has the potential to support the replacement of up to 60% FM with defatted SM in pikeperch feed without deteriorating growth, feed utilisation, and survival rate. Further, YH incorporation mitigated the damaging impacts of high SM diet on liver function and non-specific immune response.

Antibacterial and immunoregulatory activity of an antimicrobial peptide hepcidin in loach (Misgurnus anguillicaudatus)

Antimicrobial peptides (AMPs) are members of humoral immunity and particpate in resisting microbial invasion. In this study, an AMP gene hepcidin was obtained from the oriental loach Misgurnus anguillicaudatus and named Ma-Hep. This Ma-Hep encodes a peptide of 90 amino acids, with a predicted active peptide segment (Ma-sHep) of 25 amino acids at C terminus. Stimulation by a bacterial pathogen Aeromonas hydrophila resulted in significant up-regulation of Ma-Hep transcripts in loach midgut, head kidney, and gill. Ma-Hep and Ma-sHep proteins were expressed in Pichia pastoris and their antibacterial activity was examined. Results showed that Ma-sHep possessed stronger antibacterial activity against various Gram-positive and Gram-negative bacteria, compared to Ma-Hep. Scanning electron microscopy showed that Ma-sHep might kill bacteria by destroying bacterial cell membranes. Moreover, we found that Ma-sHep had an inhibitory effect on blood cell apoptosis induced by A. hydrophila and facilitated the bacterial phagocytosis and clearance in loach. Histopathological analysis indicated Ma-sHep could protect liver and gut of loach from bacterial infection. Ma-sHep has high thermal stability and PH stability, which is conducive to further feed addition. Feed supplemented with Ma-sHep expressing yeast improved the intestinal flora of loach by increasing the dominant bacteria and decreasing the harmful bacteria. Feed supplemented with Ma-sHep expressing yeast also regulated the expression of inflammatory related factors in various tissues of loach and reduced the mortality of loach upon bacterial infection. These findings show that the antibacterial peptide Ma-sHep is involved in the antibacterial defense of loach and can be used as a candidate for new antimicrobial agents in aquaculture.

Dietary yeast glycoprotein supplementation improves the growth performance, intestinal health and disease resistance of largemouth bass (Micropterus salmoides) fed low-fishmeal diets

The active ingredients extracted from yeast are important for regulating animal health. The aim of the current research was to explore the impacts of dietary yeast glycoprotein (YG) on the growth performance, intestinal morphology, antioxidant capacity, immunity and disease resistance of largemouth bass (Micropterus salmoides). A total of 375 juvenile fish (6.00 ± 0.03 g) were allocated into 15 fiberglass tanks. Triplicate tanks were assigned to each diet. The dietary YG inclusion was as follows: the first group was given a high fishmeal diet (40% fishmeal, 0% YG) (FM) and the second group was given a low fishmeal diet (30% fishmeal and 15% soybean meal, 0% YG) (LFM). The fish in the third, fourth and fifth groups were fed the LFM diet supplemented with 0.5% (LFM+YG0.5), 1.0% (LFM+YG1.0) and 2.0% (LFM+YG2.0) YG, respectively. After a 60- day feeding trial, a challenge test using A. hydrophila was carried out. The results showed that the final body weight (FBW) and weight gain rate (WGR) in the LFM+YG2.0 group were significantly higher than those in the LFM group and were no significantly different from those in the FM group. This may be partially related to the activation of the target of rapamycin (TOR) signaling pathway. Dietary YG supplementation enhanced intestinal physical barriers by upregulating the intestinal tight junction protein related genes (claudin1, occludin and zo2) and improving the structural integrity of the gut, which may be partially associated with AMPK signaling pathway. Moreover, dietary YG increased the antioxidant capacity in the gut, upregulated intestinal anti-inflammatory factors (il-10, il1-1β and tgf-β) and downregulated proinflammatory factors (il-1β and il-8), which may be partially related to the Nrf2/Keap1 signaling pathways. The results of the challenge test indicated that dietary supplementation with 0.5 or 1.0% YG can increase the disease tolerance of largemouth bass against A. hydrophila. In conclusion, the present results indicated that dietary supplementation with YG promotes the growth performance, intestinal immunity, physical barriers and antioxidant capacity of largemouth bass. In addition, 1.0% of dietary YG is recommended for largemouth bass based on the present results.

Yeast hydrolysate attenuates lipopolysaccharide-induced inflammatory responses and intestinal barrier damage in weaned piglets

BACKGROUND

Intestinal inflammation is the main risk factor causing intestinal barrier dysfunction and lipopolysaccharide (LPS) can trigger inflammatory responses in various eukaryotic species. Yeast hydrolysate (YH) possesses multi-biological effects and is received remarkable attention as a functional ingredient for improving growth performance and promoting health in animals. However, there is still inconclusive on the protective effects of dietary YH supplementation on intestinal barrier of piglets. This study was conducted to investigate the attenuate effects of YH supplementation on inflammatory responses and intestinal barrier injury in piglets challenged with LPS.

METHODS

Twenty-four piglets (with an average body weight of 7.42 ± 0.34 kg) weaned at 21 days of age were randomly assigned to one of two dietary treatments (12 replications with one pig per pen): a basal diet or a basal diet containing YH (5 g/kg). On the 22^nd d, 6 piglets in each treatment were intraperitoneally injected with LPS at 150 μg/kg BW, and the others were injected with the same amount of sterile normal saline. Four hours later, blood samples of each piglet were collected and then piglets were euthanized.

RESULTS

Dietary YH supplementation increased average daily feed intake and average daily gain (P < 0.01), decreased the ratio of feed intake to gain of piglets (P = 0.048). Lipopolysaccharide (LPS) injection induced systemic inflammatory response, evidenced by the increase of serum concentrations of haptoglobin (HP), adrenocorticotropic hormone (ACTH), cortisol, and interleukin-1β (IL-1β). Furthermore, LPS challenge resulted in inflammatory intestinal damage, by up-regulation of the protein or mRNA abundances of tumor necrosis factor-α (TNF-α), IL-1β, toll-like receptors 4 (TLR4) and phosphor-nuclear factor-κB-p65 (p-NFκB-p65) (P < 0.01), and down-regulation of the jejunal villus height, the protein and mRNA abundances of zonula occludens-1 (ZO-1) and occludin (OCC; P < 0.05) in jejunal mucosa. Dietary YH supplementation decreased the impaired effects of ACTH, cortisol, HP, IL-1β and diamine oxidase in serum (P < 0.05). Moreover, YH supplementation also up-regulated the jejunal villus height, protein and mRNA abundances of ZO-1 and OCC (P < 0.05), down-regulated the mRNA expressions of TNF-α and IL-1β and the protein abundances of TNF-α, IL-1β, TLR4 and p-NFκB-p65 in jejunal mucosa in LPS-challenged pigs (P < 0.01).

CONCLUSION

Yeast hydrolysate could attenuate inflammatory response and intestinal barrier injury in weaned piglets challenged with LPS, which was associated with the inhibition of TLR4/NF-κB signaling pathway activation.

Effects of Five Prebiotics on Growth, Antioxidant Capacity, Non-Specific Immunity, Stress Resistance, and Disease Resistance of Juvenile Hybrid Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

To explore the short-term health benefits of five prebiotics on hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), six experimental groups fed with different diets (basal diet, diet control (CON); basal diet + 0.2% fructooligosaccharide (FOS), diet FOS; basal diet + 0.5% chitosan, diet chitosan (CTS); basal diet + 0.2% mannan-oligosaccharide (MOS), diet MOS; basal diet + 0.1% β-glucan (GLU), Diet GLU; basal diet + 0.05% xylooligosaccharide (XOS), diet XOS) were set up, and a 4-week feeding trial was conducted. MOS and XOS significantly improved the growth of hybrid grouper compared to the CON group (p < 0.05). Antioxidant enzyme assay showed that the activity of glutathione peroxidase (GPx) was significantly enhanced in the MOS group, and the content of malondialdehyde (MDA) in the XOS group was significantly lower than in the CON group (p < 0.05). The catalase (CAT) activities were significantly enhanced in all prebiotic-supplemented groups compared with the CON group (p < 0.05). Non-specific immunity assay showed that the activities of alkaline phosphatase (AKP) and lysozyme (LZM) were significantly increased in all prebiotic-supplemented groups compared with the CON group (p < 0.05). The total protein content in the XOS group was significantly increased (p < 0.05), and the albumin (ALB) activity in the MOS group was more significantly increased than that in the CON group. Histological examination of the intestine revealed that muscle thickness was significantly increased in all prebiotic-supplemented groups compared to the CON group (p < 0.05). Villi length, villi width, muscle thickness all increased significantly in the MOS group (p < 0.05). In addition, the crowding stress and ammonia nitrogen stress experiments revealed that the survival rates of the MOS and XOS groups after stresses were significantly higher than those of the CON group (p < 0.05). Though MOS and XOS exhibited similar anti-stress effects, the antioxidant and non-specific immunity parameters they regulated were not the same, indicating that the specific mechanisms of MOS and XOS's anti-stress effects were probably different. After being challenged with Vibrio harvey, MOS and GLU groups showed significantly higher post-challenge survival rates than the CON group (p < 0.05). These findings indicated that among the five prebiotics, MOS and XOS showed the best overall short-term beneficial effects and could be considered promising short-term feed additives to improve the stress resistance of juvenile hybrid grouper.

Dietary supplementations modulate the physiological parameters, fatty acids profile and the growth of red claw crayfish (Cherax quadricarinatus)

An optimal diet is an important factor for the proper growth and health of crustaceans. However, the regulation of antioxidant activity and non-specific immunity related to the consumption of feed additives has not been studied in RC-crayfish. Triplicate groups of 20 crayfish/tank (36.72 ± 0.70 g) fed with a basal diet and sixteen experimental diets that contained five feed additives with four grade levels (40, 160, 240 and 320 mg/kg vitamin E, 2, 4, 6 and 8 g/kg nucleotides, 2, 4, 6 and 8 g/kg Haematococcus pluvialis, 5, 10, 15 and 20 g/kg arachidonic acid and 2.5, 5, 10 and 15 g/kg yeast extract) on physiological parameters, fatty acids profile and growth of Cherax quadricarinatus for a period of 70 days by using orthogonal array method (L16 4⁵ ). The results showed that the antioxidants activity in the haemolymph and hepatopancreas were both higher in crayfish fed with diets NO. 9 to 12 than others. Also, all the diets except diets NO. 13 to 16 showed lower free radicals contents than the control group. Similarly, significantly higher non-specific immune parameters were observed in the hepatopancreas of crayfish supplementations than those fed a control diet. Biochemical parameters related to protein profile in haemolymph increased in diets NO. 9 to 12 and then decreased in control and diets NO. 13 to 16, while the highest biochemical parameters related to lipid profile except HDL-c contents in haemolymph were observed in crayfish fed the control diet. Fatty acid composition in the hepatopancreas, muscle and ovary of RC-crayfish was significantly influenced by using the combination of Vit E, NT, H. pluvialis and YP compared to the control group. Compared to all treatments, RC-crayfish fed with diets NO. 2 and 12 had significantly stimulated higher growth performance and feed utilisation. Overall, our results suggest that diets supplemented with Vit E level of 240 mg/kg, in combination with 8 g/kg NT, 4 g/kg, H. pluvialis, 5 g/kg ARA and 10 g/kg YP are the promising treatments to increase antioxidants activity, non-specific immune response, fatty acids composition and growth of RC-crayfish. However, high dietary supplementations level can reduce antioxidants activity, immunity and inhibit growth.

Dietary phosphorus supplementation in the diet of Pacific white shrimp (Litopenaeus vannamei) alleviated the adverse impacts caused by high Clostridium autoethanogenum protein

The study evaluated the effects of dietary phosphorus supplementation on the fishmeal replacement with Clostridium autoethanogenum protein (CAP) in the diet of L. vannamei. Four isonitrogenous and isolipid diets were formulated: the PC diet contains 25% fishmeal, the NC, P1 and P2 diets were replaced 40% fishmeal with CAP and supplemented with 0, 0.8 and 1.6% NaH₂PO₄ respectively (equivalent to dietary phosphorus level of 0.96%, 1.12% and 1.27%). Sampling and V. parahaemolyticus challenge test were conducted after 50-day-feeding (initial shrimp weight 1.79 ± 0.02 g). The results showed that there were no significant differences in the growth performance of shrimp among the 4 groups. The expressions of dorsal in the gut were significantly lower in shrimp fed the P1 and P2 diets than shrimp fed the NC diet and the expression of peroxinectin in the gut was lower in shrimp fed the NC diet than others. The cumulative mortality of shrimp after V. parahaemolyticus challenge was significantly lower in shrimp fed the P2 diet than those fed the NC diet. After the challenge, genes expressions related to the prophenoloxidase activating system (proPO, lgbp, ppaf) were inhibited in the hepatopancreas of shrimp fed NC diet but activated in shrimp fed the P1 diet compared to those fed the PC diet. The AKP and T-AOC activities were higher in shrimp fed the P2 diet than those fed the other diets. The thickness of muscle layer of shrimp fed the P1 diet was thicker than that in the other groups, and significant stress damage happened in the midgut of the shrimp fed the NC diet. The abundance of Pseudoalteromonas, Haloferula and Ruegeria in shrimp fed the P1 diet was higher than those fed the other diets, while Vibrio in shrimp fed the P2 diet was higher than those fed the other diets. This indicated that a low fishmeal diet with dietary phosphorus level of 1.12% could improve the histology, enhance immune response, and increase the abundance of beneficial bacteria in the gut of shrimp. The low fishmeal diet with dietary phosphorus level of 1.27% could improve disease resistance and antioxidant capacity, but there was a possibility of damage to the gut histology as well as increasing abundance of Vibrio in the gut microbiota of shrimp.

Squid industry by-product hydrolysate supplementation enhances growth performance of Penaeus monodon fed plant protein-based diets without fish meal

The poor growth of aquatic animals fed with diets containing high plant proteins has been attributed to low diet acceptability and feed value. Supplementation of protein hydrolysate, with high contents of free amino acids and soluble low molecular weight peptides, may increase the acceptability and feed value of a plant protein-based diet. In the present work, squid processing by-products were enzymatically hydrolyzed and used as a supplement in a plant protein-based diet, without fish meal, of Penaeus monodon to fully maximize the utilization of this marine resource. The hydrolysate was incorporated at 0, 0.5, and 1% levels in P. monodon diets containing 0 and 10% fish meal levels. Growth, digestive enzyme activities, muscle growth-, gut pro-inflammatory and immune-related gene expressions, and muscle morphometric measurements were evaluated as biological indices in an 8-week feeding trial. The squid by-product hydrolysate produced in the present study contains 90.25% protein, 5.84% lipid, and 3.91% ash, and has a molecular weight of 3.76 kDa. Supplementation at 1% hydrolysate in the experimental shrimp diet without fish meal resulted in the highest growth performance associated with increased feed intake, efficient feed and nutrient conversion and retention, enhanced digestive enzyme activities, upregulation of muscle growth- and immune-related genes, and suppression of the gut pro-inflammatory gene. The growth promotion is also linked with a significant increase in muscle mean fiber area, which suggests hypertrophic growth in shrimp. Generally, the supplementation of 1% squid by-product hydrolysate supported the growth of P. monodon fed on a plant protein-based diet without fish meal.

Effects of recombinant anti-lipopolysaccharide factor expressed by Pichia pastoris on the growth performance, immune response and disease resistance of Litopenaeusvannamei

The codon-optimized anti-lipopolysaccharide factor (ALF) sequence was introduced into pPICZαA vector and transformed into Pichia pastoris GS115. The recombinant ALF yeast supernatant (rALF-mix) was freeze-dried and evaluated as a feed additive for Litopenaeus vannamei. It was found by antibacterial activity test in vitro that the rALF-mix had antibacterial activity under different pH and temperature conditions. The 0, 0.00375%, 0.0075%, 0.015%, 0.03% and 0.06% of rALF-mix were added respectively to make the six experimental diets. After a 10-week feeding trial with shrimps (2.36 ± 0.02 g), it was found that the weight gain rate (WGR) and protein efficiency ratio (PER) of shrimp in the groups with 0.0075%, 0.015% and 0.03% of dietary rALF-mix supplementation were significantly higher than those in the control group (P < 0.05). Dietary rALF-mix supplementation significantly increased the total haemocyte count, respiratory burst, phagocytic activity, total anti-oxidative capacity (T-AOC), phenol oxidase activity, nitric oxide synthase activity, lysozyme (LYZ) activity, serum antibacterial capacity in the hemolymph and the T-AOC, LYZ in the hepatopancreas of shrimps (P < 0.05). The malondialdehyde contents in hemolymph and hepatopancreas were significantly decreased (P < 0.05). Meanwhile, the expression levels of toll, immune deficiency, heat shock protein 70, crustin and lipopolysaccharide-β-glucan binding protein in the gill of shrimps were significantly increased (P < 0.05). After the challenge test, it was showed that dietary rALF-mix supplementation significantly improved the resistance of L. vannamei to Vibrio parahaemolyticus (P < 0.05). In conclusion, the rALF-mix can be used as a functional feed additive to improve the growth, immunity and disease resistance of shrimp. Based on the quadratic regression analysis for WGR, the optimal supplemental level of rALF-mix in diet for shrimp was estimated to be 0.02813%.

Effects of Compound Feed Attractants on Growth Performance, Feed Utilization, Intestinal Histology, Protein Synthesis, and Immune Response of White Shrimp (Litopenaeus Vannamei)

To investigate the effects of compound attractants on the growth performance, feed utilization, intestinal morphology, protein synthesis, and immune response of Litopenaeus vannamei, the following seven diets were formulated: a positive control (P), a negative control (N), and five diets with compound attractants which were labeled as A, B, C, D, and E, each with four of five tested attractants (yeast extract, squid visceral powder, fish soluble, and squid paste, shrimp paste), respectively. Shrimp (0.71 ± 0.00 g) were distributed to seven groups of four replicates and fed for 7 weeks. Results showed that the final body weight, feed intake, specific growth rate, and weight gain of shrimp in the B and D groups were the greatest. Hemolymph total antioxidant capacity of shrimp in the B, D, and E groups reached the highest level. In the hepatopancreas, the activity of total nitric oxide synthase, malondialdehyde content, the expression levels of sod, myd88, eif4e2, and raptor in shrimp fed the B diet were the highest, and the highest levels of dorsal and relish were observed in the C group. In the intestine, intestinal muscle thickness and expression levels of toll and eif2α in the C group were the highest, while the highest expression level of sod and relish occurred in the B group. In summary, the B and E diets promoted the feed intake, growth performance and the antioxidant enzyme activity of L. vannamei. The C diet enhanced the protein synthesis of shrimp. Regression analysis indicated that the WG and FI of shrimp were increased as the dietary inclusion levels of squid paste and shrimp paste increased, while they were decreased as the dietary inclusion levels of yeast extract and fish soluble increased.

Single-Cell Proteins Obtained by Circular Economy Intended as a Feed Ingredient in Aquaculture

The constant increment in the world’s population leads to a parallel increase in the demand for food. This situation gives place the need for urgent development of alternative and sustainable resources to satisfy this nutritional requirement. Human nutrition is currently based on fisheries, which accounts for 50% of the fish production for human consumption, but also on agriculture, livestock, and aquaculture. Among them, aquaculture has been pointed out as a promising source of animal protein that can provide the population with high-quality protein food. This productive model has also gained attention due to its fast development. However, several aquaculture species require considerable amounts of fish protein to reach optimal growth rates, which represents its main drawback. Aquaculture needs to become sustainable using renewable source of nutrients with high contents of proteins to ensure properly fed animals. To achieve this goal, different approaches have been considered. In this sense, single-cell protein (SCP) products are a promising solution to replace fish protein from fishmeal. SCP flours based on microbes or algae biomass can be sustainably obtained. These microorganisms can be cultured by using residues supplied by other industries such as agriculture, food, or urban areas. Hence, the application of SCP for developing innovative fish meal offers a double solution by reducing the management of residues and by providing a sustainable source of proteins to aquaculture. However, the use of SCP as aquaculture feed also has some limitations, such as problems of digestibility, presence of toxins, or difficulty to scale-up the production process. In this work, we review the potential sources of SCP, their respective production processes, and their implementation in circular economy strategies, through the revalorization and exploitation of different residues for aquaculture feeding purposes. The data analyzed show the positive effects of SCP inclusion in diets and point to SCP meals as a sustainable feed system. However, new processes need to be exploited to improve yield. In that direction, the circular economy is a potential alternative to produce SCP at any time of the year and from various cost-free substrates, almost without a negative impact.

Modulation of growth performance, antioxidant capacity, non-specific immunity and disease resistance in largemouth bass (Micropterus salmoides) upon compound probiotic cultures inclusion

An 8-week feeding trial was conducted to evaluate the effects of dietary supplementation of compound probiotic cultures (CPC; Bacillus subtilis, Lactobacillus plantarum and Saccharomyces cerevisiae) on the growth performance, antioxidant capacity, non-specific immunity and disease resistance of juvenile largemouth bass. Triplicate groups of largemouth bass (average weight 42.05 ± 0.02 g), with a destiny of 30 individuals per tank, were fed diets supplemented with different concentration of compound probiotic cultures (CPC) (0%, CPC (0.0); 0.5%, CPC (0.5); 1.0%, CPC (1.0); 2.0%, CPC (2.0)). After the feeding trial, tissue samples of largemouth bass were collected and the challenge test with Aeromonas hydrophila was performed. Results indicated that the CPC supplementation produced no significant difference on the growth performance, feed utilization and body composition of largemouth bass, while significantly increased the cumulative survival rate in the Aeromonas hydrophila challenge test. Meanwhile, the inclusion of CPC elevated the hepatic antioxidant capacity, and the highest activity of antioxidant enzymes, including T-AOC, CAT, GPx and T-SOD, was observed in the CPC (2.0) group. Meanwhile, the transcription of Nrf2/keap1 and antioxidant related genes, including CAT, GPx, GST, SOD1 and SOD2, was significantly elevated with the inclusion of CPC. In addition, the inclusion of CPC improved the non-specific immunity of largemouth bass. The activity of serum lysozyme was significantly elevated in the CPC (2.0) group, while the transcription of RelA and pro-inflammatory factors, including TNF-α and IL-1β, was inhibited with the inclusion of CPC. Meanwhile, related genes potentially linked to RelA, including TLR2 and p38 MAPK, were detected that their relative expression was significantly inhibited with the inclusion of CPC. The current findings indicated that the inclusion of 2% CPC improved the antioxidant capacity, non-specific immunity and disease resistance of juvenile largemouth bass, and suggested that 2% CPC as a functional additive could be applied to the diet of juvenile largemouth bass in aquaculture practice.

The Effect of Dietary Saccharomyces cerevisiae on Growth Performance, Oxidative Status, and Immune Response of Sea Bream (Sparus aurata)

The objective of this study was to evaluate the beneficial effect of Saccharomyces cerevisiae (SC) on growth, intestinal morphometric characteristics, blood indices, redox balance, expression of immune-related genes, and their involvement in disease resistance in sea bream (Sparus aurata). Three hundred healthy sea bream fingerlings were allocated into equal four groups (15 fish per hapa). The first group was served as a control and received a basal diet, while the other three groups were fed diets containing 1, 2, and 4 g/kg diet SC, respectively. At the end of week 16, the daily weight gain, specific growth rate, and feed utilization were significantly higher in the SC2 and SC4 groups than the control (p < 0.05). SC dose-dependently improved intestinal morphology, and the 4 g/kg diet significantly increased dry matter, crude fat, and crude protein percentage of body composition when compared with the control group. The 4 g/kg SC boosted innate immune response and phagocytic activity, and all SC-supplemented diets improved total protein, glucose, triglycerides, and urea concentrations, as well as intestinal digestive enzymatic activities. All estimated oxidative markers were significantly enhanced in the group that received 4 g/kg SC when compared with the control and other SC groups (p < 0.05). Feeding the fish a diet supplemented with 4 g/kg SC markedly regulated the expression of HSP70, IGF1, and IL-1β genes. In addition, the 4 g/kg SC-supplemented diet was the most effective in protecting the fish against Vibrio parahaemolyticus challenge. In conclusion, SC-enriched diet improved growth performance, intestinal morphology, redox homeostasis, and immune response of S. aurata with the 4 g/kg concentration as the most effective.

Combined administration routes of marine yeasts enhanced immune-related genes and protection of white shrimp (Penaeus vannamei) against Vibrio parahaemolyticus

Antibiotic usage to control infectious diseases in shrimp aquaculture has led to serious problems on antimicrobial resistance. An alternative to mitigate this issue is the use of probiotics, which can be easily administered by feed and water. This study examines immunomodulatory and protective effects of the marine yeasts Debaryomyces hansenii CBS8339 (Dh) and Yarrowia lipolytica Yl-N6 (Yl) -alone and mixed-in white shrimp Penaeus vannamei post-larvae. Administration routes (fed and water alone or in combination), supplementation frequency and time elapsed after the last dietary supplement were tested on growth and gene expression of penaeidin, lectin, lysozyme, superoxide dismutase, catalase, and peroxidase, as well as survival upon Vibrio parahaemolyticus IPNGS16 challenge. Penaeidin and lectin genes were upregulated in post-larvae fed orally with Yl or combined Dh + Yl. Higher growth and survival for yeast supplementation treatments were observed compared to the control group, mainly when yeasts (Dh + Yl) and administration routes (feed and water) were combined. In conclusion, mixed yeast and combined administration routes improved growth and immunity against V. parahaemolyticus.

Effects of yeast hydrolysate on growth performance, serum parameters, carcass traits, meat quality and antioxidant status of broiler chickens

BACKGROUND

Yeast hydrolysate (YH) has multiple salutary biological activities. Nevertheless, the application of YH in broiler production is limited. This study was conducted to evaluate the protective effects of YH derived from Saccharomyces cerevisiae by exploring growth performance, serum parameters, organs relative weight, carcass traits, meat quality and antioxidant status of broilers.

RESULTS

Supplementing YH linearly and quadratically improved (P < 0.05) body weight gain and gain-to-feed ratio compared to that in the control group. Triglycerides, low-density lipoprotein cholesterol and total cholesterol in serum, the decline in pH and cooking loss of breast muscle, and malonaldehyde concentration in serum and liver were decreased linearly and/or quadratically by YH (P < 0.05), whereas high-density lipoprotein cholesterol in serum, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in serum, GSH-Px activity in liver, glutathione content in serum and liver, eviscerated yield rate and chest muscle yield, and the relative weight of spleen and liver were linearly and/or quadratically increased (P < 0.05). Moreover, YH enhanced the mRNA levels of nuclear factor erythroid 2-related factor 2, heme oxygennase-1 (HO-1), GSH-Px1 and SOD1 (linear and/or quadratic, P < 0.05).

CONCLUSION

Dietary YH beneficially affected growth performance, serum parameters, organ relative weight, carcass traits, meat quality and antioxidant status in broilers, indicating its potential application as a promising feed additive in broiler production. © 2021 Society of Chemical Industry.

Evaluation of Dietary Probiotic Bacteria and Processed Yeast (GroPro-Aqua) as the Alternative of Antibiotics in Juvenile Olive Flounder Paralichthys olivaceus

We investigated the three probiotic bacteria and a processed yeast (GroPro-Aqua) as the replacers of antibiotics in juvenile olive flounder. A total of seven diets were used, that is, one basal or control (CON) diet; and six other diets, of which, three diets were prepared by supplementing probiotic bacteria such as Bacillus subtilis WB60 (BSWB60) at 1 × 10⁸ CFU/g diet, Bacillus subtilis SJ10 (BSSJ10) at 1 × 10⁸ CFU/g diet, and Enterococcus faecium SH30 (EFSH30) at 1 × 10⁷ CFU/g diet; one diet with processed yeast (GRO) at 0.35% diet; and two other diets were supplemented with oxytetracycline (OTC) and amoxicillin (AMO) at 4 g/kg of each. Triplicate groups of fish (average 12.1 g) were fed one of the diets for eight weeks. At the end of the feeding trial, the fish that were fed the probiotic bacteria-supplemented diets had a significantly higher final weight, weight gain, and specific growth rate compared to the CON, OTC, and AMO diets. Fish that were fed the GRO diet had significantly higher feed efficiency and protein efficiency ratios than those of the fish that were fed the CON diet. Serum glutamic pyruvic transaminase, glutamic oxaloacetic transaminase, glucose, and total protein were not affected by the diets. Lysozyme activity in fish that were fed the BSSJ10, BSWB60, and EFSH30 diets were significantly higher compared to the CON and OTC diets, whereas myeloperoxidase activity of fish fed the BSWB60 and EFSH30 diets were significantly higher than those of fish fed the CON and AMO diets. Flounder growth hormone gene expressions of fish that were fed BSWB60 and GRO diets were significantly higher compared to the CON, OTC, and AMO diets. The interleukin-1β gene expression of fish that were fed the BSSJ10, BSWB60, EFSH30, OTC, and GRO diets was significantly higher than those of fish fed the CON diet. The interleukin-10 gene expression of fish that were fed the BSSJ10, EFSH30, and GRO diets was significantly higher than those of fish fed the CON and AMO diets. Posterior intestinal histology of fish showed significantly higher villi length in fish that were fed the BSSJ10, BSWB60, EFSH30, and GRO diets compared to the CON diet. After 15 days of challenge test with pathogenic bacteria Edwardsiella tarda, the cumulative survival rate of fish that were fed the BSSJ10, BSWB60, EFSH30, and GRO diets were significantly higher than those of fish that were fed the CON diet. Overall, the results indicate that dietary supplementation of B. subtilis (10⁸ CFU/g diet), E. faecium (10⁷ CFU/g diet), and processed yeast (GroPro-Aqua at 0.35% diet) could replace the antibiotics in terms of improving growth, immunity, gut health, and disease resistance in juvenile olive flounder.

Effects of yeast hydrolysate supplementation on intestinal morphology, barrier, and anti-inflammatory functions of broilers

Objective

This study was conducted to evaluate the effects of dietary yeast hydrolysate (YH) supplementation on intestinal morphology, barrier, and anti-inflammatory functions of broilers.

Methods

A total of 320 one day old male broilers were randomly allocated into four groups with eight replicates of ten broilers each. The broilers were supplemented with a basal diet (the control group) or basal diets adding 50, 100, 150 mg/kg YH, respectively. This trial lasted for 42 days. The orthogonal polynomial contrasts were used to determine the linear and quadratic effects of increasing levels of YH.

Results

In our previous research, supplementing YH improved growth performance by enhancing body weight gain but decreased feed-to-gain ratio. In this study, compared with the control group, dietary YH addition linearly and quadratically decreased serum diamine oxidase activity (p<0.05). Additionally, supplementing YH linearly and/or quadratically decreased jejunal crypt depth (CD), tumor necrosis factor-alpha (TNF-α) concentration as well as mucin 2, interleukin-6 (IL-6), IL-1β, TNF-α, nuclear factor kappa B, and myeloid differentiation factor 88 gene expression levels (p<0.05). Whereas the jejunal villus height (VH), VH/CD, IL-10 concentration as well as zonula occludens-1 and IL-10 gene expression levels were linearly and/or quadratically increased by YH supplementation (p<0.05).

Conclusion

Dietary YH supplementation improved intestinal morphology, barrier and anti-inflammatory functions while decreased intestinal permeability of broilers, which might be related with altering pertinent genes expression. This study provides evidence of YH as a promising feed additive for broilers.

Reconstruction of Litopenaeus vannamei Genome-Scale Metabolic Network Model and Nutritional Requirements Analysis of Different Shrimp Commercial Varieties

As an important tool for systematic analysis, genome-scale metabolic network (GSMN) model has been widely used in various organisms. However, there are few reports on the GSMNs of aquatic crustaceans. Litopenaeus vannamei is the largest and most productive shrimp species. Feed improvement is one of the important methods to improve the yield of L. vannamei and control water pollution caused by the inadequate absorption of feed. In this work, the first L. vannamei GSMN named iGH3005 was reconstructed and applied to the optimization of feed. iGH3005 was reconstructed based on the genomic data. The model includes 2,292 reactions and 3,005 genes. iGH3005 was used to analyze the nutritional requirements of five different L. vannamei commercial varieties and the genes influencing the metabolism of the nutrients. Based on the simulation, we found that tyrosine-protein kinase src64b like may catalyze different reactions in different commercial varieties. The preference of carbohydrate utilization is different in various commercial varieties, which may due to the different expressions of some genes. In addition, this investigation suggests that a rational and targeted modification in the macronutrient content of shrimp feed would lead to an increase in growth and feed conversion rate. The feed for different commercial varieties should be adjusted accordingly, and possible adjustment schemes were provided. The results of this work provided important information for physiological research and optimization of the components in feed of L. vannamei.

Dietary supplementation of marine yeast Yarrowia lipolytica modulates immune response in Litopenaeus vannamei

The immunostimulatory potential of the marine yeast Yarrowia lipolytica (D1 and N6 strains) administered orally was evaluated in the white shrimp Litopenaeus vannamei. Yeasts and commercial glucans were mixed with a commercial feed to formulate diets with a 1.1% concentration of immunostimulants. The shrimp were fed daily for a period of 21 days. Weekly determinations were performed for immunological parameters in hemolymph, such as total hemocyte count (THC), lysozyme activity (LYZ), prophenoloxidase activity, antioxidant enzymatic activities (superoxide dismutase [SOD], catalase [CAT], and peroxidases), and bactericidal activity against Vibrio parahaemolyticus. Expression profiles of penaeidin (PEN), lysozyme (LYZ), and prophenoloxidase (proPO) immune genes were evaluated in hemocytes. In general, an increase in the immune parameters was observed in shrimp fed yeast diet compared to glucan and the control diets. Yarrowia lipolytica, especially strain N6, provided maximum immunostimulatory effects evidenced by the increase of immune parameters (THC, LYZ, SOD, CAT) and gene expression profile. In conclusion, this study demonstrated that Y. lipolytica had immunostimulatory effects and increased bactericidal activity in L. vannamei hemocytes against V. parahaemolyticus. These findings open the path for the potential application of Y. lipolytica-based immunostimulant for shrimp aquaculture.

Improvement of growth, intestinal short-chain fatty acids, non-specific immunity and ammonia resistance in Pacific white shrimp (Litopenaeus vannamei) fed dietary water-soluble chitosan and mixed probiotics

This study was to explore the impacts of water-soluble chitosan and mixed probiotics on growth performance, intestinal short-chain fatty acids (SCFAs) and immunity and ammonia resistance in Litopenaeus vannamei. Shrimp were fed one of four experimental diets including basal diet (CON), 0.10% water-soluble chitosan diet (WSC), 0.30% mixed probiotics (MP) and 0.10% water-soluble chitosan +0.30% mixed probiotics (SYN) for 8 weeks. Results showed shrimp fed with dietary MP and SYN diets could significantly improve growth performance and feed utilization in comparison with those of shrimp fed with CON diet (P < 0.05). Acetic acid content was significantly higher in shrimp fed with all supplemented diets compared to that in shrimp fed with CON diet (P < 0.05). Compared to shrimp fed with CON diet, dietary WSC and MP significantly influenced the contents and/or activities of aspartate aminotransferase (AST), total protein (TP), superoxide dismutase (SOD), lysozyme (LZM) in serum, SOD, malondialdehyde (MDA), acid phosphatase (ACP) in hepatopancreas and SOD and MDA in intestine. In addition, the gene expression levels of prophenoloxidase (proPO), penaiedin 3a (Pen-3a), crustin (Crustin), serine proteinase (SP), GPX and SOD in hepatopancreas, were significantly upregulated compared to those in CON diet at some time points (P < 0.05). Significantly higher survival rate in all supplemented diets were observed after ammonia challenge (P < 0.05). Therefore, the above results indicated dietary WSC and MP or SYN could enhance intestinal SCFAs content, stimulated antioxidant capacity and immune response, and increase the ammonia resistance of Litopenaeus vannamei. Besides, the growth performance was also improved by dietary MP and SYN.

Effects of reducing dietary fishmeal with yeast supplementations on Litopenaeus vannamei growth, immune response and disease resistance against Vibrio harveyi

The aim of this experiment was to investigate the effects of reducing dietary fishmeal (FM) with yeast culture (SYC) supplementation on growth, immune response, intestinal microbiota, intestinal morphology, and disease resistance of Litopenaeus vannamei. A total of 480 shrimps with an average initial body weight of 0.35 ± 0.002 g were randomly distributed into twelve tanks. Three isonitrogenous (40.00 crude protein) and isolipidic (8.00 crude lipids) diets with yeast culture supplementing fishmeal were formulated. The groups were divided into two (2) namely control group and experimental groups. The formulations of the groups were control (0 %, without yeast culture) and the experiment groups (SYC) [(1 % of yeast culture), and (2 % of yeast culture)]. Each diet was delivered in four replicate per treatment group. The results indicate significant improvement on the growth indices (specific growth rate, weight gain rate, survival rate and lower feed conversion ratio) with yeast culture treatment group after 56 days feeding trials (P < 0.05). Total hemolymph protein, superoxide dismutase, catalase, alkaline phosphatase, acid phosphatase, lysozyme and phenoxidase were enhanced but low aspartate aminotransferase, alanine aminotransferase, and glucose were observed in shrimp fed yeast culture diets (P < 0.05). The SYC groups showed insignificant differences in hemolymph cholesterol and triglyceride. Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant bacteria found in all the SYC groups. At the genus level, Vibrio was significantly decreased (P < 0.05) in 2 % yeast culture diets supplemented group whereas the beneficial bacteria Pseudoalteromonas was significantly enhanced. Moreover, intestinal villus length and width in shrimps fed yeast culture diets were improved (P < 0.05). Dietary yeast culture supplementation can improve growth, intestinal health, immune response, and resistance against Vibrio harveyi infections in L. vannamei.

Effects of dietary yeast culture on shrimp growth, immune response, intestinal health and disease resistance against Vibrio harveyi

The current study was conducted to evaluate the effects of different levels of yeast culture (YC) supplementation at 0% (YC 0%), 1% (YC 1%), and 2% (YC 2%) on growth, feed conversion ratio, body composition, intestinal morphology, microflora, immune response, and resistance to Vibrio harveyi infection in Litopenaeus vannamei. After 8-weeks feeding trial, the results showed significant improvement (p < .05) in the final weight, weight gain rate, specific growth rate, survival rate and low feed conversion ratio in YC groups than the control. Serum total protein, superoxide dismutase, catalase, alkaline phosphatase, acid phosphatase, lysozyme, and phenol oxidase in shrimps fed diet YC (2%) were significantly higher (p < .05), whereas significantly decreased trend in serum cholesterol, triglyceride, aspartate aminotransferase, and alanine aminotransferase (p < .05) were observed in YC (2%) diet. Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes were the core phylum bacteria found in the shrimp intestines. At the genus level, opportunistic pathogenic bacteria, Vibrio was significantly decreased (p < .05) while beneficial bacteria Pseudoalteromonas was increased in YC (2%) group. Intestinal villus height and width in shrimps fed YC diets were significantly improved than the control diet (p < .05). YC groups challenged test significantly showed (p < .05) improved shrimps immune response against V. harveyi infections with YC (2%) recording the highest percentage survival rate (70%). The present study demonstrated that supplementing YC (2%) can improve growth, intestinal microbiota, intestinal morphology, and immune response against V. harveyi infections in L. vannamei.

The effects of dietary yeast hydrolysate on growth, hematology, antioxidant enzyme activities and non-specific immunity of juvenile Nile tilapia, Oreochromis niloticus

The present study was aimed to compare and evaluate the impacts of supplemented diets with different yeast hydrolysate (YH) levels on growth performance, body composition, hematological characteristics, antioxidant enzyme activities, and non-specific immunity (intestinal cytokines) of juvenile Nile tilapia (Oreochromis niloticus). Three isonitrogenous (protein, 33%) and isolipidic (lipid, 6%) experimental diets supplemented graded levels of YH (0% for control; 1% and 3% as tested diets) were fed to juvenile Nile tilapia. A total of 240 fish with initial body weight averaging 3.5 ± 0.02 g were randomly divided into three groups with four replicates per group and 20 fish for each replicate. For apparent satiation, the fish were fed twice daily during eight weeks. The results showed no significant difference in survival among all treatments. The fish fed the diet containing 1% yeast hydrolysate had significantly elevated weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) compared to the control group and lower feed conversion ratio (FCR). The fish fed 1% and 3% YH showed higher glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT) activity and a significantly lower malondialdehyde (MDA) level in the liver than the control group, indicating enhancement of the anti-oxidant status. Serum lysozyme activity was significantly increased in the diet having 1% and 3% yeast hydrolysate supplementation groups, suggesting an improvement influence on the non-specific immune response. The expression of IL-1β, IL-10, TNF-α, TGF-β2, ALP and TLR2 was significantly elevated in fish fed the diet containing 1% YH. In conclusion, dietary supplementation with 1% yeast hydrolysate improves growth performance, and feed utilization enhances the antioxidant status and exerts an adequate stimulus on the non-specific immunity (intestinal cytokines) of Nile tilapia.

Fermented Animal Source Protein as Substitution of Fishmeal on Intestinal Microbiota, Immune-Related Cytokines and Resistance to Vibrio mimicus in Freshwater Crayfish (Cherax cainii)

A feeding trial was carried out to evaluate the effects of substitution of fishmeal (FM) by dietary poultry by-product meal, fermented by Lactobacillus casei and Saccharomyces cerevisiae on growth, intestinal health, microbial composition, immune related cytokines and disease resistance of freshwater crayfish, marron (Cherax cainii) against Vibrio mimicus. Two isonitrogenous and isocaloric diets were formulated by replacing FM protein with fermented poultry by-product meal (FPBM) protein at 0% (Control) and 75% (FPBM), and fed marron for 70 days. The results indicated no significant difference (P > 0.05) in final body weights between two groups of marron, whilst intestinal microvilli number per fold was increased in marron fed FPBM than the control. The 16S rRNA sequences revealed an increased number of Lactobacillus and Streptococcus, and decreased number of Aeromonas at genus level in the distal intestine of marron fed FPBM. Marron fed FPBM showed up-regulated expression of IL-8, IL-10, and IL-17F genes in the distal intestine. Significantly (P < 0.05) increased lysozyme and phagocytic activity, and higher survival was found in marron fed FPBM following a bacterial challenge with Vibrio mimicus. Therefore, it is concluded that FPBM is beneficial to marron in terms of microbial community, immune-related cytokines and disease resistance against V. mimicus.

Recent advances in single cell protein use as a feed ingredient in aquaculture

The global demand for high-quality, protein-rich foods will continue to increase as the global population grows, along with income levels. Aquaculture is poised to help fulfill some of this demand, and is thus the fastest growing animal protein industry. A key challenge for it, though, is sourcing a sustainable, renewable protein ingredient. Single cell protein (SCP) products, protein meals based on microbial or algal biomass, have the potential to fulfill this need. Here, we review potential sources of SCP strains and their respective production processes, highlight recent advances on identification of new SCP strains and feedstocks, and, finally, review new feeding trial data on important aquaculture species, specifically Atlantic salmon, rainbow trout, and whiteleg shrimp.

Effects of dietary yeast hydrolysate on the growth, antioxidant response, immune response and disease resistance of largemouth bass (Micropterus salmoides)

A 56-day growth trial was conducted to investigate the effects of dietary yeast hydrolysate on the growth performance, antioxidation, immune response and resistance against Aeromonas hydrophila in largemouth bass. Four experimental diets were prepared with yeast hydrolysate levels of 0% (Y0), 1.5% (Y1.5), 3.0% (Y3.0) and 4.5% (Y4.5). Each diet was randomly assigned to triplicate 150-L tanks and each tank was stocked with 30 largemouth bass (initial body weight, IBW = 7.71 ± 0.02 g). A challenge test was carried out after the feeding trial by injecting A. hydrophila intraperitoneally for 4-day observation. The results showed that the FBW and WGR in Y1.5 group were significantly higher than those in Y0 group (P < 0.05) and the feed conversion ratio (FCR) got the lowest value in Y1.5 group. And the hydrolysate supplement significantly increased the 4-day cumulative survival rate after the bacterial challenge (P < 0.05). The plasma malondialdehyde was lower in the yeast hydrolysate supplement groups in both pre- and post-challenge test (P < 0.05), while the plasma C3 increased (P < 0.05). In post-challenge test, the plasma superoxide dismutase (SOD) and catalase (CAT) activities increased in the Y1.5 and Y3.0 groups respectively (P < 0.05), and plasma lysozyme in Y1.5 group and the plasma IgM in Y3.0 group were higher than those in others respectively (P < 0.05). For the q-PCR results, in post-challenge test, the hepatic hep2 expression level in Y1.5 and Y4.5 groups were both significantly higher than those in others (P < 0.05), as well as il-8 in Y3.0 group. The spleen hif-1alpha and tgf-beta1 expression levels in Y4.5 group were all significantly lower than those in others (P < 0.05), while the gilt was significantly higher (P < 0.05) in the post-challenge test. And the expression levels of spleen tnf-alpah1 in Y1.5 and Y3.0 groups and il-8 in Y3.0 group were all significantly higher than those in other groups (P < 0.05) in the post-challenge test. The head kidney gilt expression level was significantly higher in the yeast hydrolysate supplement groups compared with the Y0 group (P < 0.05), and the head kidney il-8 expression level in Y1.5 group was significant higher than those in other groups in post-challenge test (P < 0.05). The present results indicated dietary yeast hydrolysate improved the antioxidant ability and enhanced the immune response of largemouth bass without negative effect on growth. And 1.5% or 3.0% of dietary yeast hydrolysate was recommended for largemouth bass based on the present results.

Effects of dietary anthocyanin on innate immune parameters, gene expression responses, and ammonia resistance of Nile tilapia (Oreochromis niloticus)

The present study investigated the effects of dietary anthocyanin on the growth performance, haematological, non-specific immune, and spleen gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 8.24 ± 0.64 g were used in the study; four of these were fed with diets incorporating anthocyanin (20 mg kg -¹, 40 mg kg^-1, 80 mg kg^-1 and 160 mg kg^-1), while the fifth was a control group without dietary anthocyanin. Growth performance and haematological parameters of tilapia were not affected by anthocyanin-supplemented diets (p > 0.05). Dietary anthocyanin significantly increased respiratory burst activity, phagocytic activity, phagocytic index, lysozyme activity, myeloperoxidase activity, serum total superoxide dismutase (T.SOD) activity, and serum catalase (CAT) activity (p < 0.05). The total immunoglobulin level was highest in the 80 mg kg^-1 group compared with the other groups (p < 0.05). In addition, with the anthocyanin-containing diets, the gene levels of interleukin 1, beta (IL-1β), interleukin 8 (IL-8), tumor necrosis factor (TNF-α), heat shock protein 70 (HSP70), and interferon gamma (IFN-γ) were increased in the fish spleen, and the gene levels of CAT, GPx, and SOD were also increased in fish liver (p < 0.05). At the end of the experiment, the fish were subjected to ammonia stress. The groups fed with 20 and 40 mg kg^-1 anthocyanin exhibited higher survival rates than the other groups. In summary, feeding Nile tilapia with anthocyanin-containing diets caused increases in the innate immune parameters, gene expression responses, and the survival rate of the fish subjected to ammonia stress.

Intestinal bacterial signatures of the "cotton shrimp-like" disease explain the change of growth performance and immune responses in Pacific white shrimp (Litopenaeus vannamei)

Imbalance of intestinal microbiota has been recognized in aquatic animals infected with various diseases. However, the signature of intestinal bacteria of the "cotton shrimp-like" disease in the Pacific white shrimp Litopenaeus vannamei remains unknown. This study investigates the composition, diversity, microbial-mediated function and interspecies interaction of intestinal microbiota on shrimp with different health status using 16S rRNA gene high-throughput sequencing. Meanwhile, the growth performance and the mRNA expression of innate immune gene in hepatopancreas were also investigated. The growth performance and the mRNA expression of innate immune genes (e.g., crustin, toll, and immune deficiency genes) in the hepatopancreas were significantly decreased in diseased shrimp compared with healthy shrimp. Bacteria of the family Rickettsiaceae and genus Tenacibaculum were exclusively enriched and significantly increased in diseased shrimp, respectively, whereas, the Actinobacteria class dramatically deceased. The diseased shrimp exhibited higher ACE and Chao1 indices and lower complexity of intestinal interspecies interaction than healthy shrimp. Microbial-mediated functions predicted by PICRUSt showed that 83% KEGG pathway including nutrient absorption and digestion significantly increased in diseased shrimp. This study provides an overview on the interplay among the "cotton shrimp-like" disease, intestinal microbiota, growth performance and host immune responses from an ecological perspective.

Individual and combined effects of ammonia-N and sulfide on the immune function and intestinal microbiota of Pacific white shrimp Litopenaeus vannamei

In this study, we explored the individual and combined effects of ammonia-N and sulfide stress (1 mg/L sulfide and 15 mg/L ammonia-N) on the oxidation resistance, immune response and intestinal health of Litopenaeus vannamei during 72 h exposure. The total antioxidant capacity (T-AOC), malonaldehyde (MDA) and nitric oxide (NO) content, superoxide dismutase (SOD) and catalase activity (CAT), the immune-relative gene (caspase-3, hsp70 and IMD) expression in hepatopancreas and intestine of L.vannamei and the intestinal microbiota were measured. The result showed that MDA and NO contents in hepatopancreas of L. vannamei in all treatment groups increased and remain were at high levels at the end of the stress exposure. The L. vannamei employ antioxidant defense system by increasing the activities of T-AOC, SOD and CAT enzymes in hepatopancereas and intestine to reduce oxidant damage. More severe damages with combined ammonia-N and sulfide stress to antioxidant systems were observed. The gene expression results also demonstrated that antioxidant capacity of L. vannamei was severely impaired and the apoptosis cell was initiated under the ammonia-N and sulfide stress. In addition, the environmental stress also reshaped the intestinal microbial community structure of L. vannamei that a number of original genera decreased, such as Cellvibrio, Vibrio and Rheinheimera; some new genera increased or appeared, such as Photobacterium in all treatment groups, Arcobacter and Fusibacter in sulfide stress group. Therefore, the health of L. vannamei was severely impacted when exposed to the stress of ammonia nitrogen and sulfide and these two factors can have weak synergic effects.

Differential Transcriptomic and Metabolomic Responses in the Liver of Nile Tilapia (Oreochromis niloticus) Exposed to Acute Ammonia

Ammonia is toxic to aquatic animal. Currently, only limited works were reported on the responses of aquatic animals after ammonia exposure using "omics" technologies. Tilapia suffers from the stress of ammonia-nitrogen during intensive recirculating aquaculture. Optimizing ammonia stress tolerance has become an important issue in tilapia breeding. The molecular and biochemical mechanisms of ammonia-nitrogen toxicity have not been understood comprehensively in tilapia yet. In this study, using RNA-seq and gas chromatograph system coupled with a Pegasus HT time-of-flight mass spectrometer (GC-TOF-MS) techniques, we investigated differential expressed genes (DEGs) and metabolomes in the liver at 6 h post-challenges (6 hpc) and 24 h post-challenges (24 hpc) under high concentration of ammonia-nitrogen treatment. We detected 2258 DEGs at 6 hpc and 315 DEGs at 24 hpc. Functional enrichment analysis indicated that DEGs were significantly associated with cholesterol biosynthesis, steroid and lipid metabolism, energy conservation, and mitochondrial tissue organization. Metabolomic analysis detected 31 and 36 metabolites showing significant responses to ammonia-nitrogen stress at 6 and 24 hpc, respectively. D-(Glycerol 1-phosphate), fumaric acid, and L-malic acid were found significantly down-regulated at both 6 and 24 hpc. The integrative analysis of transcriptomics and metabolomics suggested considerable alterations and precise control of gene expression at both physiological and molecular levels in response to the stress of ammonia-nitrogen in tilapia.

Effects of dietary hydrolyzed yeast (Rhodotorula mucilaginosa) on growth performance, immune response, antioxidant capacity and histomorphology of juvenile Nile tilapia (Oreochromis niloticus)

An 8 weeks feeding experiment was conducted to evaluate the effects of dietary supplementation with hydrolyzed yeast (HY) (Rhodotorula mucilaginosa) on growth performance, hematological parameters, immune response and antioxidant ability of juvenile Nile tilapia. Five isonitrogenous and isolipidic diets (32% protein and 4% lipid) with different levels (0%, 0.125%, 0.25%, 0.5%, 1%) of HY were formulated. Each diet was randomly assigned to quadruplicate groups of fish (initial body weight 19.1 ± 0.01 g). Results indicated that significantly higher specific growth rate (SGR) and lower feed conversion rate (FCR) were obtained in fish fed 1% HY diet than that of fish fed 0% HY diet (P < 0.05). Fish fed 0.25% HY diet showed the lowest value of hepatopancreas somatic indices (HSI) and significantly lower than that of fish fed 0% HY diet (P < 0.05). Meanwhile, protein and ash in the whole-body content of fish fed 1% HY diet was significantly higher than that of fish fed 0%-0.5% HY diets. Serum immunological parameters showed that the lysozyme (LZM) activity and Complement C3 content were significantly increased by dietary supplementation of 0.5%-1% HY (P < 0.05). However, dietary supplementation with 0.125%-1% HY significantly decreased the activity of myeloperoxidase (MPO) (P < 0.05). Antioxidant status in serum and liver was significantly enhanced by dietary supplementation of 0.25%-1% HY through the remarkably improved superoxide dismutase (SOD) activity both in serum and liver, the raised total antioxidative capacity (T-AOC) of serum as well as the notably reduced malondialdehyde (MDA) content in the liver (P < 0.05). However, T-AOC in the liver was not significantly influenced among all diet treatments (P > 0.05). Villi height and intraepithelial lymphocytes (IEFs) of mid-intestine were significantly higher in fish fed 0.5%-1% HY diets (P < 0.05). The challenge test demonstrated the enhanced protection against Streptococcus iniae strain by the obtained higher cumulative survival rate. In conclusion, dietary supplementation of 1% HY could maintain the better growth performance, nutrient composition as well as immune response and antioxidant capacity for juvenile Nile tilapia.

Effects of dietary yeast extract supplementation on growth, body composition, non-specific immunity, and antioxidant status of Chinese mitten crab (Eriocheir sinensis)

This study was conducted to evaluate the effects of dietary supplementation with yeast extract on growth, body composition, non-specific immunity, and antioxidant status of Chinese mitten crab (Eriocheir sinensis). A total of 432 crabs (initial average weight, 4.62 ± 0.11 g) were randomly distributed into four treatment groups with six replicates of 18 crabs. The crabs were fed a basal diet or the same diet supplemented with 2.5, 5, and 10 g/kg yeast extract for 8 weeks. The results showed that dietary yeast extract inclusion enhanced the edible viscera index (linear, P < 0.001), edible viscera crude protein (CP) content (linear, P = 0.025) and serum phenoloxidase (ProPO) activity (quadratic, P = 0.023) at 56 day, increased the total superoxide dismutase (T-SOD) activity at 28 day (quadratic, P = 0.037) and catelase (CAT) activity at 56 day (quadratic, P = 0.034) of edible viscera, and muscular T-SOD activity (quadratic, P = 0.020) at 56 day in Chinese mitten crab. Compared with the control group, the inclusion of 5 g/kg yeast extract in the diet increased the edible viscera index, enhanced the CAT activity of edible viscera at 56 day in Chinese mitten crab (P < 0.05). Dietary 10 g/kg yeast extract inclusion enhanced the edible viscera index at 56 day in Chinese mitten crab than that of the control group (P < 0.05). These results implied that dietary yeast extract inclusion improved the edible viscera index and crude protein content of edible viscera, enhanced serum immunity, and increased the antioxidant status of edible viscera and muscle in Chinese mitten crab, especially when it is supplemented at 5 g/kg yeast extract in the diet.