Dietary supplementation of mannan oligosaccharide improves the immune responses and survival of marron, Cherax tenuimanus (Smith, 1912) when challenged with different stressors

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.

Probiotics, Prebiotics, and Synbiotics Utilization in Crayfish Aquaculture and Factors Affecting Gut Microbiota

Aquaculture is affected by numerous factors that may cause various health threats that have to be controlled by the most environmentally friendly approaches. In this context, prebiotics, probiotics, and synbiotics are frequently incorporated into organisms' feeding rations to ameliorate the health status of the host's intestine, enhancing its functionality and physiological performance, and to confront increasing antimicrobial resistance. The first step in this direction is the understanding of the complex microbiome system of the organism in order to administer the optimal supplement, in the best concentration, and in the correct way. In the present review, pre-, pro-, and synbiotics as aquaculture additives, together with the factors affecting gut microbiome in crayfish, are discussed, combined with their future prospective outcomes. Probiotics constitute non-pathogenic bacteria, mainly focused on organisms' energy production and efficient immune response; prebiotics constitute fiber indigestible by the host organism, which promote the preferred gastrointestinal tract microorganisms' growth and activity towards the optimum balance between the gastrointestinal and immune system's microbiota; whereas synbiotics constitute their combination as a blend. Among pro-, pre-, and synbiotics' multiple benefits are boosted immunity, increased resistance towards pathogens, and overall welfare promotion. Furthermore, we reviewed the intestinal microbiota abundance and composition, which are found to be influenced by a plethora of factors, including the organism's developmental stage, infection by pathogens, diet, environmental conditions, culture methods, and exposure to toxins. Intestinal microbial communities in crayfish exhibit high plasticity, with infections leading to reduced diversity and abundance. The addition of synbiotic supplementation seems to provide better results than probiotics and prebiotics separately; however, there are still conflicting results regarding the optimal concentration.

From waste to feed: Microbial fermented abalone waste improves the digestibility, gut health, and immunity in marron, Cherax cainii

New aquafeed ingredients produced by a circular economy approach are the opportunity for sustainable and resilient aquaculture. In the light of this approach, the mixture of abalone waste and Sargassum spp (9:1) fermented by Saccharomyces cereviceae and Lactobacillus casei (Yakult®) (FMAS) were used to replace 0% (FMAS0), 25% (FMAS-25), 50% (FMAS-50), 75% (FMAS-75), and 100% (FMAS-100) of fishmeal (FM) protein in marron, Cherax cainii diet. The marron was fed these diets in triplicate for 90 days. Growth, feed utilization and protein efficiency ratio were unchanged in marron-fed all test diets. Improvement in apparent protein digestibility was aligned with an increase in the size and number of B-cells in the hepatopancreas. Most of the immune responses, except for haemocyte clotting time, hyaline cells and neutral red retention time (NRR time) were unchanged by 42- and 90-days feeding trials compared to those of the control group. 90 days post-feeding marron with FMAS25 showed a lower haemocyte clotting time than the post 42 days feeding marron with the same diet. Hyaline cells increased in marron fed FMAS75 for 90 days compared to marron fed the same diet for 42 days. The challenge test involved injecting marron with Vibrio mimicus resulted in a 100% survival rate after 96 h of exposure. During the challenge test, phagocytosis activity in 24 and 48-h post-challenged marron fed FMAS75 decreased which recovered after 96 h post-challenge. Marron fed FMAS50 also recorded a significantly higher proportion of granular cells after 24 h and NRR time at 96 h compared with that of other treatments. Given the above indicators of bio-growth, feed efficiency and immune responses, total replacement of FM protein of marron practical feed with FMAS are considered feasible and optimum to maintain health status and resistance to disease.

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.

Effects of Dietary Pectin and Lactobacillus salivarius ATCC 11741 on Growth Performance, Immunocompetence, Gut Microbiota, Antioxidant Capacity, and Disease Resistance in Narrow-Clawed Crayfish, Postantacus leptodactylus

The present study was conducted to clarify the effects of Lactobacillus salivarius (LS) ATCC 11741 and pectin (PE) on growth performance, digestive enzymes activity, gut microbiota composition, immune parameters, antioxidant defense as well as disease resistance against Aeromonas hydrophila in narrow-clawed crayfish, Postantacus leptodactylus. During 18 weeks trial feeding, 525 narrow-clawed crayfish juvenile (8.07 ± 0.1 g) fed with seven experimental diets including control (basal diet), LS1 (1 × 10⁷ CFU/g), LS2 (1 × 109 CFU/g), PE1 (5 g/kg), PE2 (10 g/kg), LS1PE1 (1 × 10⁷ CFU/g +5 g/kg), and LS2PE2 (1 × 109 CFU/g +10 g/kg). After 18 weeks, growth parameters (final weight, weight gain, and specific growth rate) and feed conversion rate were significantly improved in all treatments (P < 0.05). Besides, diets incorporated with LS1PE1 and LS2PE2 significantly increased the activity of amylase and protease enzymes compared to LS1, LS2, and control groups (P < 0.05). Microbiological analyses revealed that the total heterotrophic bacteria count (TVC) and lactic acid bacteria (LAB) of narrow-clawed crayfish fed diets containing LS1, LS2, LS1PE1, and LS2PE2 were higher than control group. The highest total haemocyte count (THC), large-granular (LGC) and semigranular cells (SGC) count, and hyaline count (HC) was obtained in LS1PE1 (P < 0.05). Similarly, higher immunity activity (lysozyme (LYZ), phenoloxidase (PO), nitroxidesynthetase (NOs), and alkaline phosphatase (AKP)) observed in the LS1PE1 treatment compared to the control group (P < 0.05). The glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity remarkably enhanced in LS1PE1 and LS2PE2, while malondialdehyde (MDA) content reduced in these two treatments. In addition, specimens belonging to LS1, LS2, PE2, LS1PE1, and LS2PE2 groups presented higher resistance against A. hydrophila compared to the control group. In conclusion, feeding narrow-clawed crayfish with synbiotic had higher efficiency on growth parameters, immunocompetence, and disease resistance compared to single consumption of prebiotics and probiotics.

Lactobacillus acidophilus and L. plantarum improve health status, modulate gut microbiota and innate immune response of marron (Cherax cainii)

This study aimed to investigate the combined effects of two most potent probiotic bacteria Lactobacillus acidophilus and Lactobacillus plantarum on overall health and immune status of freshwater crayfish, marron under laboratory conditions. A total of 36 marron were distributed into six different tanks and two different feeding groups, control and probiotic-fed group. After acclimation, control group was fed with basal diet while probiotic group was fed 109 CFU/mL per kg of bacterial supplemented feed for 60 days. The results showed no significant differences in weight gain, however, probiotic feed significantly enhanced some hemolymph parameters and biochemical composition of tail muscle. Histology data revealed better hepatopancreas health and higher microvilli counts in the marron gut fed probiotic diet. The probiotic bacteria triggered significant shift of microbial communities at different taxa level, mostly those reported as beneficial for crayfish. The probiotic diet also enriched the metabolic functions and genes associated with innate immune response of crayfish. Further correlation analysis revealed significant association of some taxa with increased activity for hemolymph and immune genes. Therefore, dietary Lactobacillus supplementation can modulate the overall health and immunity as well as gut microbial composition and interaction network between gut microbiota and immune system in crayfish.

Effect of mannan oligosaccharides on the microbiota and productivity parameters of Litopenaeus vannamei shrimp under intensive cultivation in Ecuador

The white leg Litopenaeus vannamei shrimp is of importance to the eastern Pacific fisheries and aquaculture industry but suffer from diseases such as the recently emerged early mortality syndrome. Many bacterial pathogens have been identified but the L. vannamei microbiota is still poorly known. Using a next-generation sequencing (NGS) approach, this work evaluated the impact of the inclusion in the diet of mannan oligosaccharide, (MOS, 0.5% w/w), over the L. vannamei microbiota and production behavior of L. vannamei under intensive cultivation in Ecuador. The MOS supplementation lasted for 60 days, after which the shrimp in the ponds were harvested, and the production data were collected. MOS improved productivity outcomes by increasing shrimp survival by 30%. NGS revealed quantitative differences in the shrimp microbiota between MOS and control conditions. In the treatment with inclusion of dietary MOS, the predominant phylum was Actinobacteria (28%); while the control group was dominated by the phylum Proteobacteria (30%). MOS has also been linked to an increased prevalence of Lactococcus- and Verrucomicrobiaceae-like bacteria. Furthermore, under the treatment of MOS, the prevalence of potential opportunistic pathogens, like Vibrio, Aeromonas, Bergeyella and Shewanella, was negligible. This may be attributable to MOS blocking the adhesion of pathogens to the surfaces of the host tissues. Together, these findings point to the fact that the performance (survival) improvements of the dietary MOS may be linked to the impact on the microbiota, since bacterial lines with pathogenic potential towards shrimps were excluded in the gut.

Impacts of functional oligosaccharide on intestinal immune modulation in immunosuppressive mice

In order to research the role of soybean oligosaccharides (SBOSs) on improvements in the microenvironment of intestinal flora and immune function of cyclophosphamide (CTX) immunosuppressive mice. Via giving intragastric administration of Soybean oligosaccharide (SBOS) at the low dose (50/(kg·BW)/d), the middle dose (200 mg/(kg·BW)/d) and the high dose (500 mg/(kg·BW)/d) partly once a day, which is also 28 days in a row. At the same time, (SBOS) mice in the drug group and (CG) mice in the positive control group were given intraabdominal injection of CTX (200 mg/kg/d).The immunosuppressive mouse model (CY) was established after 72 h in the model group and the positive control group (CG) was given intragastric administration of levamisole hydrochloric acid (LMS) for 3 days, with the data of 80ug/kg/d after injection of CTX (for actually 72 h). On the 8th, 15th and 22nd day, the number of Bifidobacterium, Lactobacillus, Enterococcus and Clostridium perfringens m in the feces of mice in each dose of drug group were determined. After the test resulted, the cellular immune function, humoral immune function, monocyte/macrophage function, NK cell activity and cytokine secretion (tumor necrosis factor-α, interferon-gamma and IL-4) were measured in immunosuppressive mice each group. The results showed that 200 mg/(kg BW) soybean oligosaccharide could significantly promote the proliferation and inhibit the increase of Enterococcus in immunosuppressive mice. The soybean oligosaccharide of 500 mg/(kg BW) could dramatically promote the proliferation of both Bifidobacillus and Lactobacillus, and also inhibit the increase of both Enterobacteriaceae and Enterococcus in immunosuppressive mice. The regulatory function of SBOS on intestinal flora was positive. Soybean oligosaccharide (500 mg/(kg BW) could significantly promote the proliferation of Bifidobacillus and Lactobacillus in immunosuppressive mice and inhibit the increase of Enterococcus and Enterococcus. The proliferation of spleen lymphocytes induced by ConA, LPS in immunosuppressive mice was dose-dependent. But it was still lower than that of the normal group (CG0) (p > 0.05). The serum hemolysin level of immunosuppressive mice was significantly increased in each dose group (p < 0.05), and the level of antibody forming cells in spleen cells of each dose group was significantly increased (P < 0.05), and the level of antibody forming cells in spleen cells of each dose group was significantly higher than that of low dose group (p < 0.005), and the level of serum hemolysin in immunosuppressive mice was significantly increased in each dose group (p < 0.05). In the detection of immune effector cell activity in immunosuppressive mice, the phagocytic function of macrophages in high dose group and the natural killing activity of spleen NK cells in high dose drug group were significantly increased, which were not significantly different from those in positive control group (P < 0.05), but the expression of TNF-α, INF-γ and IL-4 cytokines in serum was increased in a dose dependent manner (p < 0.05). In conclusion, soybean oligosaccharide can significantly increase the diversity of intestinal microecology, increase the number of intestinal beneficial bacteria, has a correlation with the proliferation of Bifidobacterium and Lactobacillus in the intestinal tract, and inhibit the proliferation of harmful bacteria. The results showed that SBOS had a direct effect on the proliferation of intestinal flora under immunosuppression. Based on the improvement of intestinal microenvironment in immunosuppressive mice by soybean oligosaccharide for 25 days, the results showed that compared with the positive control group, the nonspecific and specific immunity of immunosuppressive mice in the drug group had a regulatory effect, which improved the phagocytic function of monocytes/macrophages, developed the level of antibody forming cells, enhanced the standard of the killing activity of NK cells, and promoted the expression of cytokines as well. Compared with the model group, the transformation and proliferation of spleen lymphocytes in the high and middle dose groups were remarkably increased, but all of the indexes did not reach the level of the normal blank group. By studying the improvement of intestinal microenvironment in immunosuppressive mice, to some extent, it is concluded that the proliferation of intestinal flora can improve the immunomodulatory function of the body, but it still lowers the normal immune degree, which reflects the immunomodulatory effect of the body on the stimulation of continuous external intake. The results demonstrate that the immunomodulatory ability of immunosuppressive body was insensitive to SBOS and provided a theoretical basis for the study of health care function of intestinal microenvironment improvement when SBOS acted on abnormal immune function. The results also improved the practical application value of SBOS.

Glucan and Mannan-Two Peas in a Pod

In recent decades, various polysaccharides isolated from algae, mushrooms, yeast, and higher plants have attracted serious attention in the area of nutrition and medicine. The reasons include their low toxicity, rare negative side effects, relatively low price, and broad spectrum of therapeutic actions. The two most and best-studied polysaccharides are mannan and glucan. This review focused on their biological properties.

Effects of different dietary protein sources on the immunological and physiological responses of marron, Cherax cainii (Austin and Ryan, 2002) and its susceptibility to high temperature exposure

A two phased feeding trial was conducted to evaluate the effects of alternative protein sources on the immunophysiological responses of marron. During the phase I, marron were fed with five alternative protein supplemented diets for 90 days, while in phase II, the same marron were exposed to elevated temperature (30 °C) and their immunophysiological responses were investigated post exposure. Five isoproteic (crude protein 30%) and isoenergetic diets were prepared by containing fishmeal, poultry by-product meal, feather meal, lupin meal, and meat and bone meal as the main protein source. A hundred and fifty juvenile marron (Cherax cainii) of the average weight 9.09 ± 0.21 g were randomly distributed into 15 tanks (three replicates per feeding treatments). In the Phase I, general immune response parameters, such as, total haemocyte count (THC), proportion of hyaline cells, neutral red retention time (NRRT), phagocytic rate (PR), heamolymph bacteraemia, and condition indices of marron were investigated. The highest (P < 0.05) THC among dietary protein sources was obtained in marron fed with PbM at the end of experiment. Marron fed with FeM protein sources resulted in the highest survival rate followed by PbM fed group. Longer microvilli length (3.83 ± 0.18 μm) was demonstrated in marron fed with PbM diet. Diets containing FM and PbM protein sources revealed significantly (P < 0.05) lower number of microvilli/group than diets containing FeM and LM. The results demonstrated that different dietary protein sources in the marron diets did not detect significant (P > 0.05) change of the condition indices throughout the experiment period, however highest Hiw and Hid was recorded in marron fed with PBM at day 45. The PR of marron fed dietary protein from PbM did not change significantly after temperature exposure. Increased NRRT, PR and haemolymph bacteraemia was observed with dietary feeding of FM at the end of the trial. However, results revealed that PbM could be an alternative protein source for culture of marron as reflected in terms of increased THC, longer microvillus length and improved susceptibility to high temperature exposure. Overall, result could serve as useful baseline data in developing cost effective potential diets for marron aquaculture.

Effects of partial replacement of fish meal by yeast hydrolysate on antioxidant capability, intestinal morphology, and inflammation-related gene expression of juvenile Jian carp (Cyprinus carpio var. Jian)

This study aimed to evaluate the effects of fish meal (FM) replacement by yeast hydrolysate (YH) on liver antioxidant capability, intestinal morphology, and inflammation-related genes of juvenile Jian carp (Cyprinus carpio var. Jian). A total of 600 fish (average initial weight 19.44 ± 0.06 g) were randomly selected and divided into five groups. Five isonitrogenous and isocaloric diets replacing FM by YH 0% (YH0), 1% (YH1), 3% (YH3), 5% (YH5), and 7% (YH7) were formulated. Each diet was tested in four replicates for 10 weeks. The results have shown that, compared to the control group (YH0), liver total superoxide dismutase (t-SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione (GSH) activities of fish fed YH1 and YH3 diets were significantly higher (P < 0.05). Liver malondialdehyde (MDA) concentration significantly increased as supplementation levels of YH increased from 1 to 7% (P < 0.05). Moreover, intestinal microvillus length of juvenile Jian carp fed YH diets were significantly higher than that of fish fed the control diet (P < 0.05). In proximal intestine, the relative expression levels of inflammation-related genes (ALP, IL-1β, and TNF-α) in YH7 were significantly higher than that in the control group (P < 0.05). However, in midintestine, the expression levels of these genes in YH3 were significantly lower compared to the control group (P < 0.05). The results of this study indicated that dietary replacement of FM by 3%YH could improve antioxidant capability and intestinal microvillus morphology, as well as enhance the non-specific immunity of juvenile Jian carp.

The Use of Dietary Additives in Fish Stress Mitigation: Comparative Endocrine and Physiological Responses

In the last years, studies on stress attenuation in fish have progressively grown. This is mainly due to the interest of institutions, producers, aquarists and consumers in improving the welfare of farmed fish. In addition to the development of new technologies to improve environmental conditions of cultured fish, the inclusion of beneficial additives in the daily meal in order to mitigate the stress response to typical stressors (netting, overcrowding, handling, etc.) has been an important research topic. Fish are a highly diverse paraphyletic group (over 27,000 species) though teleost infraclass include around 96% of fish species. Since those species are distributed world-wide, a high number of different habitats and vital requirements exist, including a wide range of environmental conditions determining specifically the stress response. Although the generalized endocrine response to stress (based on the release of catecholamines and corticosteroids) is detectable and therefore provides essential information, a high diversity of physiological effects have been described depending on species. Moreover, recent omics techniques have provided a powerful tool for detecting specific differences regarding the stress response. For instance, for transcriptomic approaches, the gene expression of neuropeptides and other proteins acting as hormonal precursors during stress has been assessed in some fish species. The use of different additives in fish diets to mitigate stress responses has been deeply studied. Besides the species factor, the additive type also plays a pivotal role in the differentiation of the stress response. In the literature, several types of feed supplements in different species have been assayed, deriving in a series of physiological responses which have not focused exclusively on the stress system. Immunological, nutritional and metabolic changes have been reported in these experiments, always associated to endocrine processes. The biochemical nature and physiological functionality of those feed additives strongly affect the stress response and, in fact, these can act as neurotransmitters or hormone precursors, energy substrates, cofactors and other essential elements, implying multi-systematic and multi-organic responses. In this review, the different physiological responses among fish species fed stress-attenuating diets based on biomolecules and minerals have been assessed, focusing on the endocrine regulation and its physiological effects.

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)

An 8-week feeding trial was conducted to evaluate the effects of dietary yeast hydrolysate and brewer's yeast supplementation on growth, immune-related genes expression and ammonia nitrogen stress resistance of Pacific white shrimp (Litopenaeus vannamei). Three isonitrogenous and isolipidic practical diets were formulated to contain 0% (control diet), 1% yeast hydrolysate and 1% brewer's yeast, respectively. 360 juvenile L. vannamei with an initial weight (0.88 ± 0.01 g) was randomly divided into 3 treatments in four replicates (30 shrimp per replicate). The results indicated that shrimp fed the diet containing 1% yeast hydrolysate had a significantly higher weight gain (WG), and specific growth rate (SGR) than that fed the control diet, and the lowest feed conversion ratio (FCR) was occurred in the 1% yeast hydrolysate supplementation group. Proximate composition in whole body and muscle among all treatments was not significantly influenced by the dietary yeast hydrolysate or brewer's yeast supplementation. The challenge test with ammonia nitrogen showed that lower cumulative survival was observed in those fed the control diet, and the highest cumulative survival was occurred at shrimp fed the 1% yeast hydrolysate supplementation. Shrimp fed the control diet had higher inflammation-related genes expression levels of tnf-α and il-1β in the intestine than those fed the diets supplemented with 1% yeast hydrolysate or 1% brewer's yeast, however, there was no significant difference in expression level of alp in intestine among all treatments. The relative expression levels of mTOR signal pathway genes (eif4ebp, eif4e1a, eif4e2 and p70s6k) were significantly up-regulated in the shrimp fed the diets supplemented with 1% yeast hydrolysate, and the lowest gene expression levels of eif4ebp, eif4e1a, eif4e2 and p70s6k in the intestine were occurred at the control diet. The highest expression levels of the immune-related genes (dorsal, relish, and proPO) in the intestine were observed at shrimp fed the 1% yeast hydrolysate supplementation, and the lowest expression levels of these genes were occurred at shrimp fed the control diet, however, there was no significant difference in gene expression of lysozyme among all treatments. The expression levels of penaeidin3a, crustin, proPO, and IMD in the hepatopancreas were significantly influenced by the dietary yeast hydrolysate, brewer's yeast or no yeast product supplementation, shrimp fed the 1% yeast hydrolysate supplementation had higher expression levels of these genes than those fed the control diet. The present study indicated that dietary 1% yeast hydrolysate or brewer's yeast supplementation could improve growth performance, enhance innate immunity, and strengthen resistance of ammonia nitrogen stress, and dietary 1% yeast hydrolysate supplementation provides better immunostimulatory effects than brewer's yeast of L. vannamei.

Effects of the prebiotic mannan-oligosaccharide on the stress response of feed deprived zebrafish (Danio rerio)

Feed deprivation has deleterious effects on fish behavior and stress physiology which may susceptible them to disease outbreak. Functional ingredients in diets may substantially impact the physiology and stress responses of host organisms. Here, we hypothesized that the administration of a dietary prebiotic might attenuate the negative influences of feed deprivation on the behavioral profile of anxiety and physiological responses to stress in zebrafish (Danio rerio). Fish were fed with either basal or mannan-oligosaccharide supplemented (0.4% MOS/kg diet) diets, once per day (normal-control: CN, and normal-prebiotic: PN) or once every other day (starved-control: CS, and starved-prebiotic: PS) for 8weeks. Afterwards, fish were subjected to a novel tank test to measure anxiety. Fish from the CS treatment exhibited more pronounced bottom-dwelling behavior than the other treatments. The number of transitions from the bottom to the top third of the novel tank was significantly higher in PN fish than the CS specimens. No significant differences were found between the CN and PS treatments in all of the anxiety behaviors. CS fish showed higher baseline cortisol levels than the other treatments, which was in line with higher expression of CRH gene in fish subjected to this treatment. Cortisol levels and CRH gene expression of the subjects were also measured after induction of two routine aquaculture stressors. CN and PS fish exhibited similar patterns of cortisol responses at most of the sampling times after stress, and PN specimens showed a significantly lower concentration of cortisol than the other treatments in most cases. Expression of the CRH gene was higher in feed deprived fish immediately after stress induction. Overall, the results show that feed deprivation in some cases influenced anxiety-like behaviors and elevated stress response in zebrafish juveniles; however, the addition of MOS to the diet helped deprived fish exhibit behaviors more typical of normally fed animals.

Effects of partial replacement of fish meal by yeast hydrolysate on complement system and stress resistance in juvenile Jian carp (Cyprinus carpio var. Jian)

A 10-week feeding trial was carried out to investigate the effects of dietary fish meal replacement by yeast hydrolysate (YH) on growth performance, complement system and stress resistance of juvenile Jian carp (Cyprinus carpio var. Jian) (initial average weight 19.44 ± 0.06 g). In the study, there were five groups: one control group was fed with a basal diet (YH0), and four treatment groups were fed with dietary fish meal replaced by 1% YH (YH1), 3% (YH3), 5% (YH5) and 7% (YH7), respectively. Each group had four replicates. At the end of feeding trial, twelve fish from each group (three fish per replicate) were randomly selected for assessing the growth and immunity. Meanwhile, 20 fish per replicate were injected by Aeromonas hydrophila. The results showed that (1) Replacement levels of YH significantly affected the growth of the fish with the highest values of weight gain (WG) occurred in fish fed YH3 diet. However, no significant difference in feed conversion ratios (FCR) was observed among all groups. (2) Pre-stressed plasma lysozyme activity, total protein and albumin contents and complement component 3 (C3) and complement component 4 (C4) levels of fish fed YH3 diet were significantly higher than those of fish fed YH0 diet. However, post-stressed immune parameters of fish in all groups were significantly lower. (3) There was a trend that the expression levels of the complement-related genes (c1r/s-A, c4-1, c3-H1, c5-1, fb/c2-A, mbl-2 and masp) initially increased and then decreased except mbl-2 and masp, with the maximum values observed in fish fed YH3 diet. Before stress, the expression levels of the inflammation-related genes (alp, il-1β and tnf-α) in the hepatopancreas and spleen of fish fed YH1 diet and YH7 diet were significant higher than that of fish fed YH0 diet. After stress, no significant difference in the expression levels of those genes was observed among all groups. These results indicated that FM replacement by YH could improve growth performance, enhance innate immunity, and activate complement via the alternative complement pathway (ACP) and the classical complement pathway (CCP).

Effects of synbiotics on immunity and disease resistance of narrow-clawed crayfish, Astacus leptodactylus leptodactylus (Eschscholtz, 1823)

The aim of this study was to evaluate the effects of prebiotics (mannanoligosaccharide and xylooligosaccharide), probiotics (Enterococcus faecalis and Pediococcus acidilactici) and synbiotics for 126 days on the immune responses, hemolymph indices, antioxidant enzymes, and biological responses after a 48-hour Aeromonas hydrophila exposure of sub-adult crayfish (11.45 ± 1.87 g). Most antibacterial activities were observed in the shell mucus of crayfish fed a diet containing xylooligosaccharide + E. faecalis and mannanoligosaccharide + Pediococcus acidilactici against Nocardia brasilience and Vibrio harveyi (p < 0.05). Feeding crayfish a xylooligosaccharide + E. faecalis diet increased protein levels and the activities of alkaline phosphatase and lysozyme in the shell mucus after the feeding trial and 48 h after the A. hydrophila-injection challenge (p < 0.05). The highest ratio of the lactobacillus count to the total viable count was observed in synbiotic diets (p < 0.05). Feeding crayfish a xylooligosaccharide + E. faecalis diet increased the growth rate and the resistance to the A. hydrophila-injection challenge (p < 0.05). These results revealed that feeding crayfish with synbiotic diets was more effective than a single administration with prebiotics and probiotics.

Physiological response, blood chemistry profile and mucus secretion of red sea bream (Pagrus major) fed diets supplemented with Lactobacillus rhamnosus under low salinity stress

Environmental stressors caused by inadequate aquaculture management strategies suppress the immune response of fish and make them more susceptible to diseases. Therefore, efforts have been made to relieve stress in fish by using various functional feed additives in the diet, including probiotics. The present work evaluates the effects of Lactobacillus rhamnosus (LR) on physiological stress response, blood chemistry and mucus secretion of red sea bream (Pagrus major) under low salinity stress. Fish were fed four diets supplemented with LR at [0 (LR0), 1 × 10² (LR1), 1 × 10⁴ (LR2) and 1 × 10⁶ (LR3) cells g^-1] for 56 days. Before stress, blood cortisol, urea nitrogen (BUN) and total bilirubin (T-BIL) showed no significant difference (P > 0.05), whereas plasma glucose and triglyceride (TG) of fish-fed LR2 and LR3 diets were significantly lower (P < 0.05) than those of the other groups. Plasma total cholesterol (T-CHO) of fish-fed LR3 diet was significantly (P < 0.05) lower than that of the other groups. Furthermore, total plasma protein, mucus myeloperoxidase activity and the amount of mucus secretion were significantly enhanced in LR-supplemented groups when compared with the control group (P < 0.05). After the application of the low salinity stress test, plasma cortisol, glucose, T-CHO and TG contents in all groups showed an increased trend significantly (P < 0.01) compared to the fish before the stress challenge. However, plasma total protein and the amount of secreted mucus showed a decreased trend in all groups. On the other hand, BUN, T-BIL and mucus myeloperoxidase activity showed no significant difference after exposure to the low salinity stress (P > 0.05). In addition, the fish that received LR-supplemented diets showed significantly higher tolerance against low salinity stress than the fish-fed LR-free diet (P < 0.05). The physiological status and the detected immune responses, including total plasma protein and mucus myeloperoxidase activity in red sea bream, will provide a more comprehensive outlook of the effects of probiotics to relieve stress in fish.

Effects of soybean oligosaccharides on intestinal microbial communities and immune modulation in mice

Soybean oligosaccharides (SBOSs) are potential prebiotics that may be used to improve immune function. Here, we investigated the effects of intragastric administration of SBOSs in mice to determine the effects on autochthonous intestinal microbial communities and immunological parameters. Results E: After 22-day administration, 4.0 g kg body weight (BW)^-1 SBOSs significantly enhanced the proliferation of bifidobacteria and lactic acid bacteria (LAB) as compared to the control. This dose of SBOSs also significantly increased numbers of enterococci and decreased numbers of Clostridium perfringens. Treatment with 4.0 g kg BW^-1 SBOSs also significantly increased the percentage of T-lymphocytes and lymphocyte proliferation as compared to the control, suggesting that SBOSs promoted cellular immunity in mice. Additionally, 4.0 g kg BW^-1 SBOSs induced significant differences in hemolysin production, natural killer (NK) cell activity, phagocytic activity, cytokine production, and immunoglobulin levels compared to the control.

CONCLUSION

Our data demonstrated that intragastric administration of SBOSs at a dose of 4.0 g kg BW^-1 improved the numbers of beneficial intestinal microbes and enhanced immunological function of mice. Therefore, these data supported that SBOSs may have applications as a prebiotic to improve immune responses in humans. Further studies are warranted.

Methionine hydroxy analogue enhanced fish immunity via modulation of NF-κB, TOR, MLCK, MAPKs and Nrf2 signaling in young grass carp (Ctenopharyngodon idella)

Our study investigated the effect of dietary methionine hydroxy analogue (MHA) on growth and immunity (head kidney, spleen and skin) of young grass carp (Ctenopharyngodon idella). A total of 630 grass carp (259.70 ± 0.47 g) were fed graded levels of MHA (0, 2.4, 4.4, 6.4, 8.5 and 10.5 g/kg diet) and one dl-methionine (DLM) group (6.4 g/kg diet) for 8 weeks. At the end of the feeding trial, fish were challenged with Aeromonas hydrophila for 14 days. The results indicated that optimal MHA increased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents and up-regulated mRNA levels of liver expressed antimicrobial peptide 2, hepcidin (head kidney), β-defensin-1 in the immune organs (P < 0.05), suggesting that MHA could enhance antimicrobial ability of fish. Meanwhile, optimal MHA enhanced the immune function of immune organs via down-regulating pro-inflammatory cytokines mRNA levels and up-regulated anti-inflammatory cytokines mRNA levels, which might be attributed to the down-regulation of nuclear factor κB p65, c-Rel, IκB kinase β, p38 mitogen activated protein kinase, eIF4E-binding protein1 (4E-BP1) and 4E-BP2 mRNA levels and up-regulation of inhibitor of κBα, ribosomal protein S6 kinase 1 and target of rapamycin mRNA levels (P < 0.05). In addition, optimal MHA improved cellular structure integrity of immune organs via repressing death receptor and mitochondria pathways induced apoptosis, which might be related to the down-regulation of c-Jun-N-terminal kinase mRNA levels (P < 0.05). Simultaneously, optimal MHA improved cellular structure integrity of immune organs via elevating glutathione contents, antioxidant enzymes activities and corresponding isoforms mRNA levels to attenuate oxidative damage, which might be to the up-regulation of NF-E2-related factor 2 mRNA levels and down-regulation of Kelch-like ECH-associating protein 1a mRNA levels (P < 0.05). Besides, optimal MHA improved intercellular structure integrity of immune organs via up-regulating the mRNA levels of intercellular tight junctions-related genes, which might be owing to the down-regulation of myosin light chain kinase mRNA levels (P < 0.05). In conclusion, MHA exerted a positive effect on the immune function and structural integrity of immune organs in fish. Furthermore, according to the positive effect, MHA was superior to DLM in grass carp. However, based on the growth performance, the efficacy of MHA relative to DLM was 97%. Finally, on the premise of the basal diet containing 4.01 g/kg methionine, the optimal MHA supplementation levels based on feed intake, PWG, defense against skin hemorrhage and lesion, LZ and ACP activities, IgM content, against malondialdehyde, protein carbonyl and ROS in the head kidney of young grass carp were 5.07, 5.21, 5.76, 5.90, 5.88, 5.80, 6.22, 5.68 and 6.85 g/kg diet, respectively.

Effects of astaxanthin and emodin on the growth, stress resistance and disease resistance of yellow catfish (Pelteobagrus fulvidraco)

Yellow catfish (Pelteobagrus fulvidraco) has become a commercially important fish species in China and eastern Asia. High-density aquaculture has led to congestion and excessive stress and contributed to bacterial infection outbreaks that have caused high mortality. We investigated the effects of dietary supplementation with astaxanthin and emodin alone and in combination on the growth and stress resistance of yellow catfish. After 60 days of feeding, each group of fish (control, astaxanthin, emodin, and astaxanthin plus emodin (combination) groups) was exposed to acute crowding stress for 24 h, and a subsample of fish from the four groups was challenged with the bacterial septicemia pathogen Proteus mirabilis after the end of the crowding stress experiment. Compared with the control, the astaxanthin and emodin groups showed increases in serum total protein (TP), hepatic superoxide dismutase (SOD) activity and hepatic heat shock proteins 70 (HSP70) mRNA levels at 12 and 24 h after the initiation of crowding stress. The combination group exhibited increases in alanine aminotransferase (ALT) activity, aspartate aminotransferase (AST) activity, serum TP, hepatic SOD activity and hepatic HSP70 mRNA levels within 24 h after the initiation of crowding stress. However, decreases relative to the control were observed in the serum cortisol and glucose contents in the three treatment groups at 12 and 24 h after the initiation of crowding stress, in ALT and AST activity in the astaxanthin and emodin group at 24 h after the initiation of crowding stress, and in the serum lysozyme activity, serum alkaline phosphatase (ALP) activity, and hepatic catalase (CAT) and malondialdehyde (MDA) activity in the combination group at 24 h after the initiation of crowding stress. Additionally, the cumulative mortality after P. mirabilis infection was lower in all three treatment groups (57.00%-70.33%) than in the control (77.67%). Dietary supplementation with astaxanthin and emodin decreased the specific growth rate (SGR) and weight gain (WG) of healthy yellow catfish, although significant differences in mortality were not observed. These results indicate that dietary supplementation with 80 mg/kg astaxanthin and 150 mg/kg emodin can improve the anti-oxidative capabilities, hepatic HSP70 levels, and resistance to acute crowding stress of yellow catfish. Finally, an appropriate strategy for enhance yellow catfish stress resistance and disease resistance is proposed.

Deficiency of dietary niacin impaired intestinal mucosal immune function via regulating intestinal NF-κB, Nrf2 and MLCK signaling pathways in young grass carp (Ctenopharyngodon idella)

This study investigated the effects of dietary niacin on intestinal mucosal immune and physical barrier, and relative mRNA levels of signaling molecules in the intestine of young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp (255.63 ± 0.41 g) were fed six diets containing graded levels of niacin (3.95, 14.92, 24.98, 35.03, 44.97 and 55.01 mg/kg diet) for 8 weeks. Results observed that niacin deficiency decreased lysozyme (LA) and acid phosphatase (ACP) activities, and complement 3 (C3) content in the intestine (P < 0.05), down-regulated mRNA levels of liver expressed antimicrobial peptide 2 (LEAP-2), hepcidin, interleukin 10, transforming growth factor β1 and inhibitor of κBα (IκBα) (P < 0.05), up-regulated tumor necrosis factor α, interleukin 1β, interferon γ2, interleukin 8, nuclear factor kappa B P65 (NF-κB P65), IκB kinase α (IKKα), IκB kinase β (IKKβ) and IκB kinase γ (IKKγ) in all intestinal segments of young grass carp (P < 0.05). In addition, niacin deficiency increased reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl (PC) contents, decreased glutathione content, and copper/zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferases (GST) and glutathione reductase (GR) activities in the intestine of young grass carp (P < 0.05). Additionally, niacin deficiency decreased mRNA levels of CuZnSOD, MnSOD, GPx, CAT, GST, GR, Claudin b, Claudin 3, Claudin c, Occludin, ZO-1, Claudin 15 and NF-E2-related factor 2 (Nrf2) (P < 0.05), and increased Claudin 12, Kelch-like ECH-associating protein 1a (Keap1a), myosin light-chain kinase (MLCK) and p38 mitogen-activated protein kinase (p38 MAPK) mRNA expression levels in the intestine of young grass carp (P < 0.05), while the mRNA level of Kelch-like ECH-associating protein 1b (Keap1b) did not change (P > 0.05). In conclusion, niacin deficiency decreased intestinal mucosal immune and intestinal physical function, as well as regulated mRNA levels of NF-κB P65, IκBα, IKKα, IKKβ, IKKγ, Nrf2, Keap1a, p38 MAPK and MLCK in the intestine of young grass carp. Based on the broken-line model analysis of intestinal lysozyme activity, the requirement of niacin for young grass carp (255.63 ± 0.41 g) were estimated to be 39.80 mg/kg diet.

Probiotics and prebiotics associated with aquaculture: A review

There is a rapidly growing literature, indicating success of probiotics and prebiotics in immunomodulation, namely the stimulation of innate, cellular and humoral immune response. Probiotics are considered to be living microorganisms administered orally and lead to health benefits. These Probiotics are microorganisms in sufficient amount to alter the microflora (by implantation or colonization) in specific host's compartment exerting beneficial health effects at this host. Nevertheless, Prebiotics are indigestible fiber which enhances beneficial commensally gut bacteria resulting in improved health of the host. The beneficial effects of prebiotics are due to by-products derived from the fermentation of intestinal commensal bacteria. Among the many health benefits attributed to probiotics and prebiotics, the modulation of the immune system is one of the most anticipated benefits and their ability to stimulate systemic and local immunity, deserves attention. They directly enhance the innate immune response, including the activation of phagocytosis, activation of neutrophils, activation of the alternative complement system, an increase in lysozyme activity, and so on. Prebiotics acting as immunosaccharides directly impact on the innate immune system of fish and shellfish. Therefore, both probiotics and prebiotics influence the immunomodulatory activity boosting up the health benefits in aquatic animals.

Effects of emodin and vitamin E on the growth and crowding stress of Wuchang bream (Megalobrama amblycephala)

This study aimed to investigate the effects of dietary emodin, high-dose vitamin E and their combination on the growth of Megalobrama amblycephala and its resistance to acute crowding stress. The fish were randomly divided into four groups: a control group fed with basal diet, and three treatment groups fed with basal diet supplemented with 60 mg/kg emodin (the emodin group), 500 mg/kg vitamin E (the vit E group), and 60 mg/kg emodin together with 500 mg/kg vitamin E (the combination group). After 60 days, the fish were exposed to acute crowding stress for 24 h. The results showed that the weight gain of the vit E group, specific growth rate of the vit E group, total serum protein concentration (TP) of the vit E group, serum lysozyme activity of the emodin group, serum superoxide dismutase (SOD) activity of the emodin group, hepatic heat shock protein 70 (HSP70) levels of the vit E group and the emodin group, and serum alanine aminotransferase (ALT) activity of the combination group significantly increased while the weight gain and specific growth rate of the combination group significantly decreased compared with the control group before stress. After crowding stress, the vit E group had improved serum TP 12 h post-stress, hepatic SOD activity 24 h post-stress, and hepatic HSP70 mRNA levels 12 and 24 h post-stress while the emodin group had enhanced serum SOD activity 12 and 24 h post-stress and hepatic HSP70 mRNA levels 12 and 24 h post-stress, as compared with the control. However, the serum cortisol content of the three treatment groups 12 and 24 h post-stress, ALT activity in the vit E group and emodin group 24 h post-stress, and serum alkaline phosphatase and liver catalase activity in the combination group 24 h post-stress were lower than those in the control group. The cumulative mortality was lower in the emodin, vit E, and combination group after Aeromonas hydrophila infection compared with the control group. Therefore, dietary supplementation with 60 mg/kg emodin or 500 mg/kg vitamin E can improve HSP70 mRNA levels and antioxidant capabilities, resistance to crowding stress, and growth in M. amblycephala. However, the combination of emodin and vit E does not have a synergistic effect in M. amblycephala.

Prebiotics as immunostimulants in aquaculture: a review

Prebiotics are indigestible fibers that increase beneficial gut commensal bacteria resulting in improvements of the host's health. The beneficial effects of prebiotics are due to the byproducts generated from their fermentation by gut commensal bacteria. In this review, the direct effects of prebiotics on the innate immune system of fish are discussed. Prebiotics, such as fructooligosaccharide, mannanoligosaccharide, inulin, or β-glucan, are called immunosaccharides. They directly enhance innate immune responses including: phagocytic activation, neutrophil activation, activation of the alternative complement system, increased lysozyme activity, and more. Immunosaccharides directly activate the innate immune system by interacting with pattern recognition receptors (PRR) expressed on innate immune cells. They can also associate with microbe associated molecular patterns (MAMPs) to activate innate immune cells. However, the underlying mechanisms involved in innate immune cell activation need to be further explored. Many studies have indicated that immunosaccharides are beneficial to both finfish and shellfish.

Effect of prebiotic konjac mannanoligosaccharide on growth performances, intestinal microflora, and digestive enzyme activities in yellow catfish, Pelteobagrus fulvidraco

In the present study, konjac mannanoligosaccharide (KMOS) was evaluated as a prebiotic in yellow catfish. The fish were fed with diets containing KMOS in four concentrations: 0 g kg(-1) (C), 1.0 g kg(-1) (KM1), 2.0 g kg(-1) (KM2), and 3.0 g kg(-1) (KM3) for 49 days, respectively. Another group fed with diets containing 3.0 g kg(-1) yeast cell wall mannanoligosaccharide (MOS) (M3) was set as positive control. The results indicated that fish receiving the diets supplemented with KMOS or MOS showed higher relative gain rate (RGR), specific growth rate (SGR), and lower feed conversion ratio (FCR) with significantly differences (P < 0.05) than those fed with the basal diets. Moreover, fish receiving the diets with 2.0 g kg(-1) KMOS inclusion showed higher RGR, SGR, and lower FCR (P < 0.05) than that feeding the diets supplemented with 3.0 g kg(-1) MOS. The quantities of Bifidobacterium spp. were significantly increased (P < 0.05). Meanwhile, Escherichia coli and Aeromonas spp. were significantly reduced (P < 0.05) in the fish-feeding diets with 2.0 g kg(-1) KMOS supplement. Compared with the control group, the significantly enhancement of protease and amylase activity (P < 0.05) in intestine and pancreas was observed in fish fed with diets containing KMOS or MOS. Collectively, an optimum level of KMOS inclusion in diets could modulate intestinal microflora, induce digestive enzyme activity, and improve the growth performance of yellow catfish significantly.

Effect of dietary supplementation of fructooligosaccharide (FOS) on growth performance, survival, lactobacillus bacterial population and hemato-immunological parameters of stellate sturgeon (Acipenser stellatus) juvenile

The dietary supplementation of fructooligosaccharide (FOS) in stellate sturgeon juvenile, Acipenser stellatus (with mean initial body weight of 30.16 ± 0.14 g) was evaluated for the effect on growth, autochthonous intestinal microbiata and hemato-immunological parameters for 11 weeks. FOS was added at a level of 0, 1% and 2% to the commercial pellet diet (BioMar). At the end of the experiment, growth parameters, survival rate, lactobacillus bacterial population, hematological and immunological parameters were determined. The fish fed on 1% FOS significantly showed higher final weight, WG%, SGR and PER and lower FCR compared to those of the control group (P < 0.05). Survival rate did not significantly differ between the treatments (P > 0.05). However, FOS administration resulted in lower survival. The serum lysozyme activity was significantly affected by dietary 1% FOS (P < 0.05), while respiratory burst activity was not significantly affected by dietary treatments (P > 0.05). In fish fed on the diet with 1% FOS showed a significant increase of total heterotrophic autochthonous bacterial and presumptive LAB levels (P < 0.05) compared with those fed on the diets supplemented with prebiotics. In addition to increase in WBC, RBC, MCV, hematocrit, hemoglobin and lymphocyte levels were observed in this group. These results indicated that dietary supplementation of FOS at a dose of 1% improved growth performance, beneficial intestinal microbiata and stimulate immune response of stellate sturgeon juvenile.

Effects of Oxidized Konjac glucomannan (OKGM) on growth and immune function of Schizothorax prenanti

Schizothorax prenanti is an important existemic commercial fish in River Yangtze. OKGM (Oxidized Konjac glucomannan) is a kind of polysaccharide oxidative degraded from KGM. Added 500, 1000, 2000, 4000, 8000 mg/kg OKGM into the diets of S. prenanti. After 60 days feeding trial, WGR (weight gain rate), SGR (specific growth rate), PER (protein efficiency ratio) of groups fed the diet with 8000 mg/kg OKGM was all significantly (P < 0.05) higher; FCR (feed conversion ratio) was significantly lower than the control group whose diet have no OKGM. Hepatopancreas index, spleen index of group 6 whose feed added 8000 mg/kg OKGM were significantly higher and gallbladder index was significantly lower than the control group. Erythrocyte number, leukocyte number of group 5, 6 whose feed added 4000, 8000 mg/kg OKGM were excellent significantly (P < 0.01) more than the control group. At the same time, Erythrocyte phagocytic rate, erythrocyte phagocytic index, neutrophilic granulocyte phagocytic rate, neutrophilic granulocyte phagocytic index of all the groups whose diet added OKGM were significantly higher than the control group. Content of IgM, C3 of group 4 whose feed added 2000 mg/kg OKGM were significantly more than the control group. As for activity of CAT, group 6 was significantly higher than the control group. When compared activity of SOD, group 6 was significantly higher than group 1, 2, 3. Accordingly, activity of GSH-Px of group 3, 4, 5, 6 were significantly higher than the control group. On the contrary, content of MDA, group 3, 4, 5, 6 whose feed added 1000-8000 mg/kg OKGM was excellent significantly lower than the control group. After injected Aeromonas hydrophila 21 days, only group 6 whose feed added 8000 mg/kg OKGM survived excellent significantly more than the control group. So we can draw a conclusion of that added OKGM in the diets of S. prenanti, not only promoted growth, but also improved immune function, and the best dose was 8000 mg/kg in this experiment.

Immunological responses of customised probiotics-fed marron, Cherax tenuimanus, (Smith 1912) when challenged with Vibrio mimicus

A two-phased experiment was conducted to investigate the effects of dietary supplementation of customised probiotics on marron physiology. During the first phase marron were fed probiotic supplemented feed for 70 days, while in phase two the same marron were challenged with Vibrio mimicus and their physiological responses were investigated for 4 days post-challenged. The experiment was carried out in a purpose-built room, designed for aquaculture research, using 18 of 250 L cylindrical plastic tanks. Five species of isolated probiotic bacteria from commercial probiotic products and marron's intestine were tested in this experiment. The probiotic bacteria were (Bacillus sp.); A10 (Bacillus mycoides); A12 (Shewanella sp.); PM3 (Bacillus subtilis); and PM4 (Bacillus sp.), which were added to the formulated basal marron diet (34% crude protein, 8% crude lipid, 6% ash) at a concentration of 10(8) cfu/g of feed. Immune responses of marron fed probiotics were evaluated by investigating organosomatic indices, growth rate, survival, intermoult period, total haemocytes counts (THC), proportion of granular cells (GC), bacteraemia, bacteria load in the intestine and water quality. The results showed that dietary supplementation of probiotics in marron had no significant impact on growth, intermoult period and survival of the marron. However, their supplementation improved the physiological condition of marron in terms of significantly higher tail muscle indices, THC and proportion of granular cells (GC) and reduced bacterial load in the haemolymph. The addition of probiotics in marron diets also increased the bacteria load in the marron intestine. In addition, dietary supplementation of the customised probiotics was effective in improving the resistance of marron against V. mimicus as they had higher THC, higher proportion of GC and lower presence of bacteria in their haemolymph, after marron were challenged with V. mimicus. The results also showed that probiotic Bacillus mycoides (A10) and PM4 are the most beneficial dietary probiotics for marron health.

Dietary organic selenium improves growth, survival and resistance to Vibrio mimicus in cultured marron, Cherax cainii (Austin, 2002)

To determine the effects of dietary organic selenium (OS) supplementation on the growth performance and immune competence of marron, Cherax cainii (Austin, 2002), a group of marron were fed 0.2 g kg(-1) of Sel-Plex(®) supplemented basal diet and then compared with another group (control) of marron fed basal diet without any supplementation. After 90 days of feeding, final weight, average weekly gains (AWG), relative gain rate (RGR), specific growth rate (SGR), survival, total and differential haemocyte counts (THC and DHC), were compared between the two groups. Surviving marron from each group were then divided into three sub-groups (three tanks per sub-group with seven marron per tank); (1) first sub-group was injected with 20 μL of 3.24 × 10(6) cfu Vibrio mimicus; (2) the second sub-group was injected with 20 μL normal saline and (3) the third sub-group was not subjected to injection and became the control group. THC, DHC, neutral red retention time (NRRT) and Vibrio ranks of post-injected marron were evaluated for 96 h, at every 24-h interval. The results showed that after 90 days of feeding, final weight, AWG, RGR, SGR, survival, THC, proportion of hyaline cells of OS-fed marron were significantly higher (P < 0.05) than the control group, whereas proportion of granular and semigranular cells were not affected by dietary OS. After challenging with V. mimicus, survival rate of marron without dietary OS significantly decreased (P < 0.05) as compared to the control group of marron. THC of marron in all sub-groups were significantly reduced (P < 0.05) after the challenge. However, THC and granular cells of sub-groups fed OS were higher than other sub-groups. Vibrio ranks and NRRT of marron fed OS were significantly lower and slower, respectively, than marron fed without OS. These findings demonstrated the benefits of OS inclusion in the marron diet in terms of growth, health and disease resistance.

Beta-glucan: an ideal immunostimulant in aquaculture (a review)

The major hindrance in the development and sustainability of aquaculture industry is the occurrence of various diseases in the farming systems. Today, preventive and management measures are central concern to overcome such outbreak of diseases. Immunostimulants are considered as an effective tool for enhancing immune status of cultured organisms. Among different immunostimulants used in aquaculture practices, β-glucan is one of the promising immunostimulant, which is a homopolysaccharide of glucose molecule linked by the glycoside bond. It forms the major constituents of cell wall of some plants, fungi, bacteria, mushroom, yeast, and seaweeds. Major attention on β-glucan was captivated with the gain in knowledge on its receptors and the mechanism of action. The receptor present inside the animal body recognizes and binds to β-glucan, which in turn renders the animal with high resistance and enhanced immune response. This review highlights β-glucan as an immunostimulant, its effective dosages, and route of administration and furthermore provides an outline on role of β-glucan in enhancing growth, survival, and protection against infectious pathogens pertaining to fishes and shellfishes. Study also summarizes the effect of β-glucan on its receptors, recognition of proteins, immune-related enzymes, immune-related gene expression and their mechanisms of action.

Effects of mannan oligosaccharide on the physiological responses, HSP70 gene expression and disease resistance of Allogynogenetic crucian carp (Carassius auratus gibelio) under Aeromonas hydrophila infection

We evaluated the effect of dietary supplementation with mannan oligosaccharide (MOS) on the resistance to Aeromonas hydrophi1a infection in Allogynogenetic crucian carp. The fish were randomly divided into five groups: a control group was fed with basal diet, and four treatment groups fed with basal diet supplemented with 60, 120, 240, 480 mg/kg MOS for 10 weeks, respectively. We then challenged the fish with A. hydrophi1a and recorded the mortality and the changes in serum cortisol, T3, T4, lysozyme, alkaline phosphatase (ALP), globin and hepatic total anti-oxidative capacity, superoxide dismutase (SOD), malondialdehyde (MDA) and the relative expression of heat shock protein 70 (HSP70) mRNA for a period of 7 d. Supplementation with 240 mg/kg MOS significantly increased serum ALP activity before infection, 1d and 2d after infection, serum globin concentration prior to infection, 1d and 7d after infection, serum lysozyme activity at 2d after infection, T3 concentration at 2d after infection, hepatic total anti-oxidative capacity prior to infection, hepatic SOD activity at 7d after infection and reduced serum cortisol concentration at 2d after infection, hepatic malondialdehyde content at 1d and 2d after infection. Supplementation with 480 mg/kg MOS significantly increased serum ALP activity before infection, 1d and 2d after infection, T3 content 1d after infection, T4 content prior infection and 7d after infection, serum globin concentration prior to infection, 1d and 7d after infection, serum lysozyme activity prior infection and 1d after infection, serum total anti-oxidative capacity prior to infection and 7d after infection, hepatic SOD activity at 7d after infection and the relative level of hepatic HSP70 mRNA at 2d and 7d after infection, had decreased levels of serum cortisol concentration before the infection, at 2d after infection, T4 concentration at 1d and 2d after infection, hepatic malondialdehyde content at 1d and 2d after infection. Mortality was significantly lower in the group of 240 and 480 mg/kg MOS than the control. Our results suggest that ingestion of a basal diet supplemented with 240-480 mg/kg MOS can enhance resistance against pathogenic infections in Allogynogenetic crucian carp.

Effects of dietary mannan oligosaccharide on growth performance, gut morphology and stress tolerance of juvenile Pacific white shrimp, Litopenaeus vannamei

An 8-week feeding trial was conducted to investigate the effects of dietary mannan oligosaccharide (MOS) on growth performance, gut morphology, and NH(3) stress tolerance of Pacific white shrimp Litopenaeus vannamei. Juvenile Pacific white shrimp (1080 individuals with initial weight of 2.52 ± 0.01 g) were fed either control diet without MOS or one of five dietary MOS (1.0, 2.0, 4.0, 6.0 and 8.0 g kg(-1)) diets. After the 8-week feeding trial, growth parameters, immune parameters, intestinal microvilli length and resistance against NH(3) stress were assessed. Weight gain (WG) and specific growth rate (SGR) were significantly higher (P < 0.05) in shrimp fed 2.0, 4.0, 6.0 and 8.0 g kg(-1) MOS-supplemented diets than shrimp fed control diet. WG and SGR of shrimp fed 2.0 g kg(-1) MOS-supplemented diet was the highest (P < 0.05) in all experimental groups. Survival rate (SR) of shrimp was generally similar (P > 0.05) in all experimental groups. Compared with control group, TEM analysis revealed that 2.0, 4.0, 6.0 and 8.0 g kg(-1) MOS supplementation could significantly increase (P < 0.05) the intestinal microvilli length of shrimp at the ultrastructural level. After NH(3) stress for 24 h, SR of shrimp fed 2.0, 4.0, 6.0 and 8.0 g kg(-1) MOS-supplemented diets was significantly higher (P < 0.05) than that of shrimp fed control diet. Phenoloxidase (PO) activity of 4.0 g kg(-1) MOS-supplemented group was significantly higher (P < 0.05) than that of control group under normal conditions and NH(3) stress. PO activity significantly decreased (P < 0.05) under NH(3) stress than under normal conditions. Superoxide dismutase (SOD) activity of 4.0, 6.0 and 8.0 g kg(-1) MOS-supplemented groups was significantly higher (P < 0.05) than that of control group under normal conditions. After NH(3) stress for 24 h, SOD activity of all experimental groups also significantly decreased (P < 0.05) compared to normal conditions. These results clearly indicated that dietary MOS could improve growth performance and increase the resistance against NH(3) stress in L. vannamei, and the 2.0-4.0 g kg(-1) MOS supplementation was suitable for L. vannamei.

Dietary supplementation of fructooligosaccharide (FOS) improves the innate immune response, stress resistance, digestive enzyme activities and growth performance of Caspian roach (Rutilus rutilus) fry

The present study investigated the effects of prebiotic fructooligosaccharide (FOS) on the innate immune response, stress resistance, digestive enzyme activities, growth factors and survival of Caspian Roach (Rutilus rutilus) fry. After acclimation, fish (0.67 ± 0.03 g) were allocated into 12 tanks (50 fish per tank) and triplicate groups were fed a control diet or diets containing 1%, 2% or 3% FOS. At the end of the trial (7 weeks), humoral innate immune parameters (serum Ig levels, lysozyme activity and alternative complement activity (ACH50)), resistance to salinity stress (150 g L(-1)), digestive enzyme activities (amylase, lipase and protease) and growth factors (final weight, weight gain, specific growth rate (SGR), food conversion ratio (FCR), and condition factor) were assessed. At the end of the study the innate immune responses (Ig levels, lysozyme activity and ACH50) were significantly higher in 2% and 3% FOS fed fish (P < 0.05), whereas, 1% dietary FOS only elevated serum lysozyme activity. All dietary FOS levels significantly increased resistance to a salinity stress challenge (P < 0.05) and highest survival was observed in the 3% FOS group. Similarly, digestive enzyme activities were significantly elevated with increasing levels of dietary FOS (P < 0.05). Subsequently, elevated growth performance (final weight, SGR and FCR) was observed in roach fed 2% and 3% FOS compared to the control group (P < 0.05). These results indicate that FOS can be considered as a beneficial dietary supplement for improving the immune response, stress resistance, digestive enzyme activities and growth performance of Caspian roach fry.