Activities Of Immune-related Enzymes Research Articles

Decoding the role of HIF-1α in immunoregulation in Litopenaeus vannamei under hypoxic stress

Hypoxia poses a significant challenge to aquatic organisms, especially Litopenaeus vannamei (L. vannamei), which play a vital role in the global aquaculture industry. Hypoxia-inducible factor 1α (HIF-1α) is a pivotal regulator of the organism's adaptation to hypoxic conditions. To understand of how HIF-1α affects the immunity of L. vannamei under hypoxic conditions, we conducted a thorough study involving various approaches. These included observing tissue morphology, analyzing the expression of immune-related genes, assessing the activities of immune-related enzymes, and exploring immune-related pathways. Our study revealed that RNA interference (RNAi)-mediated knockdown of HIF-1α markedly reduced HIF-1α expression in the gill (75 to 95%), whereas the reduction ranged from 2 to 43% in the hepatopancreas. Knockdown of HIF-1α resulted in increased damage to both gill and hepatopancreatic tissues in hypoxic conditions. Additionally, immune-related genes, including Astakine (AST), Hemocyanin (HC), and Ferritin (FT), as well as immune-related enzymes such as Acid Phosphatase (ACP), Alkaline Phosphatase (AKP), and Phenoloxidase (PO), exhibited intricate regulatory patterns in response to hypoxia stress following the knockdown of HIF-1α. Transcriptome analysis revealed that HIF-1α knockdown significantly impacts multiple signaling pathways, including the JAK-STAT signaling pathway, Th17 cell differentiation pathways, PI3K-Akt signaling pathway, ErbB signaling pathway, MAPK signaling pathway, chemokine signaling pathway, ribosomal pathways, apoptosis, lysosomes and arachidonic acid metabolism. These alterations disrupt the organism's immune balance and interfere with normal metabolic processes, potentially leading to various immune-related diseases. We speculate that the weakened immune response resulting from HIF-1 inhibition is due to the reduced metabolic capacity, and the existence of a direct regulatory relationship between them requires further exploration. This study greatly advances our understanding of the vital role that HIF-1α plays in regulating immune responses in shrimp under hypoxic conditions, thereby deepening our comprehension of this critical biological mechanism.

Effects of water immersion on immune, intestinal flora and metabolome of Chinese mitten crab (Eriocheir sinensis) after air exposure

Air exposure stress can induce stress response of Eriocheir sinensis and affect its normal life activities. The goal of this study was to investigate the effects of water immersion on the recovery of hepatopancreas immune-related enzyme activity, intestinal microbial diversity and metabolic level of Chinese mitten crabs after exposure to air. The results show that immersion can effectively alleviate the adverse effects of air exposure on the antioxidant capacity and immune capacity of Chinese mitten crabs, and the longer the time of immersion, the more obvious the recovery effect. Among them, the levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and acid phosphatase significantly increased after exposure to air (P < 0.05), reached a peak at 3 h, began to decline after immersion, and returned to a level close to the initial value at 24 h (P < 0.05). In addition, after exposure to air, the glucose and total cholesterol in haemolymph of Eriocheir sinensis were significantly different from the initial values (P < 0.05), gradually recovered to the initial level after re-immersion. However, changes in intestinal flora and hepatopancreas metabolism caused by air exposure did not fully recover after water exposure, and its negative effects did not completely disappear. The sequencing results showed that the species composition and diversity of intestinal microorganisms of Chinese mitten crab changed after air exposure and immersion treatment. The relative abundance of Actinomycetes increased significantly, while that of Proteobacteria and Firmicutes decreased significantly. Metabolomics analysis showed that air exposure and immersion destroyed the metabolic balance of amino acids and carnitine, reduced the level of carnitine metabolism, hindered the absorption of nutrients, and led to the accumulation of harmful substances.

Effects of dietary Silphium perfoliatum L. on the growth performance, immunity, intestinal health, and resistance against Nocardia seriolae of largemouth bass (Micropterus salmoides)

The present study was conducted to evaluate the effect of dietary Silphium perfoliatum L. on growth performance, immunity, intestinal health, and resistance against Nocardia seriolae of largemouth bass. Four dietary concentrations of S. perfoliatum L. were prepared: 0% (SPL0), 1% (SPL1), 2.5% (SPL2.5), and 5% (SPL5). After 60 d feeding, a challenge test was conducted by injecting N. seriolae intraperitoneally. The results showed that supplementing the diets with S. perfoliatum L. could promote the weight gain rate, specific growth rate, and feed intake. Meantime, S. perfoliatum L. could also enhance the activity of immune-related enzymes and improve the expression of immune-related genes in the liver. Compared to the control group, S. perfoliatum L. improved intestinal morphology and reduced the abundance of harmful bacteria in intestinal microbiota. Importantly, supplementing the diets with S. perfoliatum L. protected largemouth bass from N. seriolae infection, resulting in a relative percent survival (RPS) of 24% (SPL1), 31.99% (SPL2.5), and 43.99% (SPL5). In conclusion, the present study showed that S. perfoliatum L. could boost growth performance, enhance immunity, promote intestinal health, and improve the ability of largemouth bass against N. seriolae infection.

Integrated analysis of intestinal microbiota and transcriptome reveals that a coordinated interaction of the endocrine, immune system and gut microbiota response to heat stress in Litopenaeus vannamei

Due to the ongoing global warming, the risk of heatwaves in the oceans is continuously increasing while our understanding of the physiological response of Litopenaeus vannamei under extreme temperature conditions remains limited. Therefore, this study aimed to evaluate the physiological responses of L. vannamei under heat stress. Our results indicated that as temperature rose, the structure of intestinal and hepatopancreatic tissues was damaged sequentially. Activity of immune-related enzymes (acid phosphatase/alkaline phosphatase) initially increased before decreased, while antioxidant enzymes (superoxide dismutase and glutathione-S transferase) activity and malondialdehyde content increased with rising temperature. In addition, the total antioxidant capacity decreased with rising temperature. With the rising temperature, there was a significant increase in the expression of caspase-3, heat shock protein 70, lipopolysaccharide-induced tumor necrosis factor-α, transcriptional enhanced associate domain and yorkie in intestinal and hepatopancreatic tissues. Following heat stress, the number of potentially beneficial bacteria (Rhodobacteraceae and Gemmonbacter) increased which maintain balance and promote vitamin synthesis. Intestinal transcriptome analysis revealed 852 differentially expressed genes in the heat stress group compared with the control group. KEGG functional annotation results showed that the endocrine system was the most abundant in Organismal systems followed by the immune system. These results indicated that heat stress leads to tissue damage in shrimp, however the shrimp may respond to stress through a coordinated interaction strategy of the endocrine system, immune system and gut microbiota. This study revealed the response mechanism of L. vannamei to acute heat stress and potentially provided a theoretical foundation for future research on shrimp environmental adaptations.

Construction of suspended bagasse bioflocs and evaluation of their effectiveness in shrimp (Penaeus vannamei) aquaculture systems

This experiment was carried out to improve the operability of bioflocs technology and to better the application of bagasse, a sugarcane by-product or fibrous pulp of other plant materials, in aquaculture. Firstly, a generator device for suspended-bagasse was designed, and indigenous efficient nitrogen-reducing bacteria were screened and combined. Then a suspended-bagasse bioflocs Penaeus vannamei (initial body weight of 0.78 ± 0.33 g, density of 350 shrimp/m2) culture system was constructed with bagasse and indigenous probiotics (single probiotic or composite probiotic from the previous step) as components through the generator device. The commercial shrimp culture model with commercial probiotics applied was used as a control group with three replicates in each group. The experiment lasted for 50 days. The effects of suspended-bagasse bioflocs on the water quality, shrimp growth, and immune response in the shrimp culture system were evaluated. All experimental results were analyzed using one-way variance or linear estimation. The suspended-bagasse generator could promote rapid biofilm formation on the surface of the bagasse, and the hydraulic retention parameter can be set to 12 h. Besides, three efficient nitrogen-reducing strains were screened and identified (Halomonas alkalihila AC3–2, Rugerella sp BD15–5, and Halomonas venusta BD15–8). They were non-hemolytic, sensitive to most antibiotics, and non-pathogenic to shrimp. Their combination with Bacillus megaterium BZ5 (a previously isolated probiotic) in a 1:1:1:1 ratio resulted in the highest degradation efficiencies of 97.1% and 51.4% for ammonia and nitrite nitrogen, respectively. Furthermore, application experiments in shrimp aquaculture systems showed that suspended-bagasse flocs (with single bacteria and combined bacteria) reduced ammonia and nitrite nitrogen levels and promoted nitrification in the water of the shrimp aquaculture system. This suspended bagasse floc (with combined bacteria) system reduced water usage by 37.6% per kg of shrimp produced compared to the common culture system. Moreover, the suspended-bagasse flocs (with combined bacteria) improved hepatopancreatic digestive enzyme (trypsin, lipase, and α-amylase) and serum immune-related enzyme (lysozyme and phenol-oxidase) activity. This study indicates that it is feasible to cultivate suspended-bagasse flocs in shrimp aquaculture systems using a generator device with bagasse and probiotic bacteria as components. The flocs based on bagasse and indigenous complex bacteria can effectively reduce water exchange during shrimp aquaculture and improve shrimp production. Imperfectly, the microbial community and function of the biofilm on the surface of bagasse, which is very important for the interpretation of water quality variations, was not revealed in this experiment and needs to be refined in future work. Additionally, it is also worthwhile to evaluate the effectiveness of this device in other aquatic animal culture systems.

A newly isolated strain of Bacillus subtilis W2Z exhibited probiotic effects on juvenile red claw crayfish, Cherax quadricarinatus

Aquaculture traditionally used antibiotics, leading to environmental contamination, food residue, and antibiotic-resistant superbugs. Probiotics offer a promising antibiotic alternative. In this study, a strain of Bacillus subtilis W2Z was isolated from aquaculture environments and can inhibit pathogens in aquaculture food production through chemical compounds. Eight-weeks C. quadricarinatus cultivation experiments revealed that B. subtilis W2Z, as a probiotic, contributes to increasing the yield of red claw crayfish. The supplementation of strain W2Z in the feed enhanced the crayfish's resistance to Aeromonas hydrophila by increasing immune-related enzyme activity and improving intestinal microbiota. B. subtilis W2Z has significant potential as a bioresource for exploring probiotics in crustacean aquaculture. Adding B. subtilis W2Z to C. quadricarinatus feed at a concentration of 1 × 108 to 1 × 109 colony forming unit (CFU)/g is recommended.

Screening and identification of probiotics from the intestinal tract of largemouth bass (Micropterus salmoides) for use as a feed additive and bacterial infection control

Probiotics regulate the health of the host by influencing digestion and absorption, intestinal morphology, microbial composition, and the host's defense against infection. The genus Bacillus encompasses several known probiotics capable of surviving harsh feed processing and extended storage conditions. More importantly, these microbes can still confer probiotic benefits even when administered to animals in the form of spores. Therefore, the screening of Bacillus strains with probiotic potential holds significant importance for aquaculture. In our study, we screened a total of 75 Bacillus strains, leading to the identification of a promising candidate strain, Bacillus velezensis (BSG-2), which has the excellent performance of antagonism towards pathogenic bacteria including Aeromonas hydrophila, Edwardsiella piscicida, and Nocardia seriolae. Genome sequencing provided the evidence of the antibacterial-related genes and gene clusters associated with secondary metabolism. In addition, BSG-2 has a prominent ability to endure harsh environment and secret digestive enzymes, which indicated that BSG-2 has the potential to survive and promote digestion in the intestinal tract through the gastrointestinal tract. Importantly, feeding 56 days, BSG-2 increased activities of digestive and immune-related enzymes, and then promoted growth and decreased mortality and tissue damage of largemouth bass after Nocardia seriolae infection. Collectively, our findings demonstrate that Bacillus velezensis BSG-2 is a promising probiotic candidate offering multiple benefits for largemouth bass.

Dietary N-carbamylglutamate (NCG) supplementation improves the survival, digestive and immunological parameters by promoting ammonia excretion in Chinese mitten crab (Eriocheir sinensis), under ammonia nitrogen stress

Ammonia nitrogen is one of the most common environmental stress factors in aquaculture. The aim of this experiment was to evaluate the effects of ammonia nitrogen stress on ammonia metabolism, digestion and immune function as well as the protective effects of dietary N-carbamylglutamate (NCG) in the Chinese mitten crab (Eriocheir sinensis). Two feeds were used, namely a control feed (regular commercial feed) and an NCG feed (NCG (302.96 ± 4.07) mg/kg added). Subsequently, animals fed by these two feeds were exposed to 30 mg/L or 60 mg/L ammonia nitrogen stress (named A30 or A60) for 21 days, respectively. The rate of hemolymph ammonia excretion was significantly increased in NCG group compared to C (control) group (P < 0.05). Hemolymph ammonia levels were significantly lower in NCG A30 (NCG feed and A30) and NCG A60 (NCG feed and A60) groups compared to A30 (control feed and A30) and A60 (control feed and A60) groups (P < 0.05). Glutamate dehydrogenase and glutamine synthetase activities in the gills and hepatopancreas of NCG A60 group were significantly increased compared with the A60 group, which promoted glutamine synthesis (P < 0.05). The cumulative mortality rate of Eriocheir sinensis in NCG A30 and NCG A60 groups were effectively reduced (P < 0.05). The arginine levels of hepatopancreas were significantly increased in NCG A60 group (P < 0.05). Under ammonia nitrogen stress, NCG significantly increased the activities of trypsin, pepsin, lipase and α-Amylase in NCG feed group, and promoted feeding (P < 0.05). In hemolymph, hepatopancreas and intestine, NCG significantly increased nitric oxide synthase activity, lysozyme and phenol oxidase activities compared to the ammonia nitrogen stress group (P < 0.05). The results indicated that, NCG added in feed could decelerate the toxic effects of ammonia on Eriocheir sinensis by promoting ammonia excretion and accelerating glutamine and endogenous arginine synthesis by metabolism. Moreover, the activity of digestive enzymes and immune-related enzymes is improved.

Mechanical abrasion stimulation: Altered epidermal mucus composition and microbial community in grass carp (Ctenopharyngodon idella)

In modern high-density farming, seasonal change, fishing, transportation, and other conditions easily cause mechanical abrasion of fish skin. This leads to alterations in the material balance of the epidermal mucus composition of fish, preventing normal immune function. Subsequently, the risk of disease increases. In this study, grass carp (Ctenopharyngodon idella) was used as an object to investigate immune-related enzyme activities, structural characteristics, and physiological changes of its epidermal mucous cells caused by mechanical abrasion. Furthermore, we explored the changes in body surface mucus composition and microbial community diversity and structure. Our results showed that mechanical abrasion stimulation, significantly changed the activities of immune-related enzymes, such as lysozyme (LZM), alkaline phosphatase (AKP), and acid phosphatase (ACP) were within 24 h (P < 0.05). Their levels gradually recovered after 48 h. In contrast, no significant change was observed in superoxide dismutase (SOD) levels. The number of mucous cells increased, especially those of type I and type II mucous cells in the dorsal skin, which were significantly increased (P < 0.05). Meanwhile, the stimulation changed the metabolites composition of the fish epidermal mucus in the short term, upregulating 12-OPDA, indole, quinic acid and GSH, which are beneficial to antibacterial and anti-inflammatory, and downregulating L-saccharopine, L-2-aminoadipic acid, spermine, GSSG and ribose 5-phosphate, which disrupt protein synthesis, energy production and DNA synthesis. Additionally, these metabolite changes further affect the composition of microorganism communities, rising the abundance of certain disease-associated microorganisms, such as Acidovorax, Rhizobiaceae, Aurantimicrobium, and Leifsonia, which increases the risk of disease in fish. The findings of the present study provide a deeper understanding of the role of mucus as a component of the immune system in fish and provide a scientific basis for effective grass carp culture management and disease control.

Effects of a phytobiotic-based additive on the growth, hepatopancreas health, intestinal microbiota, and Vibrio parahaemolyticus resistance of Pacific white shrimp, Litopenaeus vannamei.

Vibrio genus is a common pathogen in aquaculture and causes acute hepatopancreatic necrosis disease (AHPND) and massive mortality of shrimp. Many studies have suggested that a single functional ingredient such as plant extract or organic acid can reduce the dependence on antibiotics and promote the growth and immunity of aquatic animals. In this study, we evaluated the effects of a phytobiotic-based compound additive (Sanacore® GM, SNGM), which had a successful trajectory of commercial application in fish farming. However, its effects on the hepatopancreas health and intestinal microbiota of shrimp after Vibrio challenge have not been well evaluated. In the present study, Pacific white shrimp were fed diets with or without supplementation of SNGM, and the SNGM grades were 0-g/kg (CON), 3-g/kg (SNGM3), and 5-g/kg (SNGM5) diets. The feed trial lasted 60 days, after which a Vibrio parahaemolyticus challenge was performed. The results showed that compared to the CON group, both the SNGM3 and SNGM5 groups had a significantly higher weight gain and a lower feed conversion ratio as well as higher survival after Vibrio parahaemolyticus challenge. In the growth trial, the SNGM3 group had a significantly increased total protein, albumin concentration, and acid phosphatase activity in hemolymph compared to the CON group. In the challenge experiment, the SNGM3 and SNGM5 groups had increased albumin and glucose contents as well as the activities of phenoloxidase, lysozyme, alkaline phosphatase, and superoxide dismutase in hemolymph. Both the SNGM3 and SNGM5 groups had improved morphology of the hepatopancreas and intestine. The SNGM5 group had alleviated gut microbiota dysbiosis induced by Vibrio infection by increasing the potential probiotic bacterium abundance (Shewanella) and decreasing the potential pathogenic bacteria abundance (Vibrio, Photobacteriuma, Pseudoalteromonas, and Candidatus_Bacilloplasma). In conclusion, the dietary phytobiotic-based additive at 3-g/kg level increased the growth and Vibrio parahaemolyticus resistance of Pacific white shrimp by promoting immune-related enzyme activities and improving the morphological structure of the hepatopancreas and intestine and the intestinal microbiota composition.

Improvement of sea buckthorn (Hippophae rhamnoides L.) flavonoids on the antioxidant and immune performance of Yellow River carp (Cyprinus carpio L.) fed high-carbohydrate diet

High-carbohydrate (HC) diets may lead to the deterioration of the antioxidant and immune properties of Yellow River carp and the healthy development of the industry. Studies in mammals have found that sea buckthorn flavonoids (SF) improve antioxidant and immune performance. Therefore, this study comprehensively evaluated the effects of SF on Yellow River carp using in vitro and feeding trials with an HC diet. Control (C, 27.23 %), high-carbohydrate (HC, 42.99 %), and HC + SF (0.1 %, 0.2 %, and 0.4 %) groups were studied in a 10-week aquaculture experiment. The main findings were as follows: (1) SF scavenged O2·‐, ·OH, and DPPH free radicals in vitro, which gradually increased with the SF concentration. (2) The antioxidant and immune performance of Yellow River carp was enhanced by dietary supplementation with SF, which involved the regulation of activities of antioxidant and immune enzymes, as well as their changes at the transcription and protein levels. In terms of antioxidant properties, compared to the HC group, HC + SF significantly decreased the activities of glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase and the contents of H2O2 and malondialdehyde in the serum and hepatopancreas. The activities of glutathione, glutathione-Px, superoxide dismutase, catalase, and total antioxidant activity in the HC-diet group. In contrast, the addition of SF increased antioxidant enzyme activity. In the hepatopancreas and muscles, SF regulated and activated Nrf2-Keap1, a key signaling pathway for oxidative stress. SF significantly increased the mRNA expression levels of downstream genes (gr, ho-1, cat, and sod) regulated by nrf2. In terms of immune performance, 0.4 % SF markedly increased the activity of immune-related enzymes. SF inhibited the gene expression of pro-inflammatory factors induced by the HC diet and promoted the gene expression of anti-inflammatory factors. In addition, the resistance of Yellow River carp to Aeromonas hydrophila was enhanced by SF. In summary, SF supplementation can reduce oxidative stress and inflammatory harm caused by the HC diet and improve the antioxidant and immune performance of Yellow River carp to varying degrees.

Role of sodium octanoate in regulating survival, growth, intestinal development, digestive and absorptive capacities, antioxidant capacity and innate immunity of large yellow croaker (Larimichthys crocea) larvae

The present study was conducted to investigate the effects of dietary sodium octanoate (So) on the survival, growth, intestinal development, digestive and absorptive capacities, antioxidant capacity and innate immunity of Larimichthys crocea larvae. Larvae (initial body weight: 7.44 ± 0.53 mg) were fed with either a control diet or diets with different levels (0.1%, 0.2%, 0.4%, and 0.8%) of So for 30 days. The results showed that larvae fed diets with 0.1%–0.4% So had significantly increased survival compared to the control. Compared to the control, larvae fed the diet with 0.4% So showed dramatically improved growth performance, although there were no significant differences between other diets. Notably, larvae fed diets with 0.2%–0.4% So displayed significantly higher fold height of intestine compared to the control group. Increased levels of selected intestinal cell proliferation and differentiation gene markers (pcna and odc) and increased activity of intestinal brush border enzymes (alkaline phosphatase and leucine aminopeptidase) further affirmed the promotional effect of So on intestinal development. Moreover, for genes related to the intestinal apical junction complex, larvae fed diets with 0.1%–0.8% So showed significantly higher mRNA expression levels of occludin and cateninα1 than the control group. Meanwhile, compared to the control, the expression of claudin1, afadin and cadherin2 significantly increased in larvae fed diets with 0.1%–0.4% So. Also, larvae fed diets with 0.1%–0.8% So showed significantly higher activity of lipase than the control group, whereas the activity of trypsin was significantly higher only in larvae fed the diet with 0.4% So. Furthermore, absorption capacity, as reflected by the activity of brush border enzymes (Na+-K+-Adenosinetriphosphatase and creatine kinase), significantly increased in larvae fed diets with 0.2%–0.4% So compared to the control. Furthermore, larvae fed the diet with 0.4% So exhibited improved antioxidant enzyme activity (catalase and total antioxidant capacity), upregulated antioxidant related gene expression (sod2, sod3, cat, and nrf2), increased antioxidant substance levels (reduced glutathione), and decreased malondialdehyde content compared to the control group. Moreover, larvae fed the diet with 0.4% So showed the highest activity of innate immune-related enzymes (lysozyme, acid phosphatase, inducible nitric oxide synthase and total nitric oxide synthase) and the highest mRNA expression of anti-inflammatory cytokines (il4/13 and arg1). In summary, the diet supplemented with 0.4% So may optimally improve larval survival and growth probably by enhancing intestinal development, digestion and absorption, antioxidant capacity, and innate immunity.

Ulva prolifera Stress in the Yellow Sea of China: Suppressed Antioxidant Capacity and Induced Inflammatory Response of the Japanese Flounder (Paralichthys olivaceus).

As the largest green macroalgal bloom in the Yellow Sea of China, the overgrowth and degradation of Ulva prolifera (U. prolifera) have a harmful effect on marine organisms and the aquaculture industry. However, the regulation mechanism of U. prolifera stress on the antioxidant capacity and inflammatory response of marine fish is still not completely understood. A 15-day exposure experiment was conducted to evaluate the effects of U. prolifera stress on the antioxidant capacity and inflammatory response of the Japanese flounder (Paralichthys olivaceus) (283.11 ± 6.45 g). The results showed that U. prolifera stress significantly decreased their survival rate. Serum total antioxidant capacity (T-AOC) and non-specific immune-related enzyme activities were significantly impacted under U. prolifera conditions. Moreover, U. prolifera stress significantly decreased T-AOC, superoxide dismutase (SOD) activity, and catalase (CAT) activities in the liver, while malondialdehyde (MDA) contents were significantly increased. Similarly, antioxidant-related gene (cat, nrf2, and keap1) expressions were synchronously downregulated in the liver under U. prolifera stress. Furthermore, U. prolifera stress significantly upregulated pro-inflammatory gene (tnf-α, il-1β, ifn-γ, and p65) expressions and the phosphorylation levels of the p38 and JNK MAPK pathways in the head kidney. In addition, endoplasmic reticulum (ER) stress-related gene and protein expressions were also upregulated in the head kidney. Overall, these results revealed that U. prolifera stress suppressed the antioxidant capacity and induced an inflammatory response in the Japanese flounder. This study could advance the understanding of the adverse effects of U. prolifera stress on marine benthic fish and promote the sustainable development of aquaculture.

Effects of lead contamination on histology, antioxidant and intestinal microbiota responses in freshwater crayfish, Procambarus clarkii

The red swamp crayfish (Procambarus clarkii) is an important farming species in China and there is a high degree of overlap between the main crayfish production areas and areas contaminated with the heavy metal lead (Pb), thus putting crayfish farming at potential risk of Pb contamination. To assess the toxic effects of Pb on crayfish, in this study they were exposed to different concentrations of Pb (0, 0.1, 1, 10, 50 mg/L) for 72 h, and 0.1 mg/L represents the level of Pb in the contaminated water. Histomorphology and activities of antioxidant or immune-related enzymes suggest that the damage of Pb to the hepatopancreas and intestine was dose- and time-dependent, with the intestine being more sensitive to Pb than the hepatopancreas. Notably, after a short period (24 h) of stress at low concentrations (0.1 mg/L) of Pb, the malondialdehyde (MDA) content and antioxidant enzymes such as catalase (CAT) and glutathione peroxidase (GSH-Px) in the intestine of crayfish showed significant changes, indicating that low concentrations of Pb were also highly detrimental to crayfish. High-throughput sequencing of the intestinal microbial community indicated that Pb exposure led to a disturbance in the relative abundance of intestinal bacteria, increasing the abundance of pathogenic bacteria (Bosea, Cloacibacterium, Legionella spp.) and decreasing the abundance of potentially beneficial bacteria (Chitinibacter, Chitinilyticum, Paracoccus, Microbacterium, Demequina, and Acinetobacter spp.). In conclusion, Pb damages the hepatopancreas and intestinal barrier of crayfish, leading to the destruction of their anti-stress ability and immune response, and at the same time disrupts the homeostasis of intestinal microbes, resulting in adverse effects on the gut. This study contributed to the assessment of the ecotoxicity of the heavy metal Pb to the crustacean aquatic animals.

Pathogenicity and inactivated vaccine treatment of Aeromonas veronii JW-4 on crucian carp

Aeromonas veronii is a common bacterium found in a variety of aquatic environments, capable of causing a diverse array of diseases in both aquatic animals and humans. Therefore, evaluating the pathogenicity of A. veronii and implementing measures to control its spread are essential. In this study, a strain JW-4, identified as A. veronii, was isolated from diseased Scaphesthes macrolepis, a grade Ⅱ protected animal in China. To investigate the pathogenicity of the strain, fish were fed with serial levels JW-4 supplemented diet or basal diet (control group 1, CG1) for 28 days (d). Results showed that JW-4 stimulated an immune response, evidenced by an increase in immune-related enzyme activities (GOT and GPT) of serum and liver and an upregulation of genes expression levels (TNF-α and IFN-γ) of liver and spleen, and these effects gradually decreased over time. Histopathological examination revealed that JW-4 could alter the tissue structure of immune organs, such as liver and kidney. These changes were accompanied by vacuolar degeneration, nuclear dissolution, and an increased lymphocyte count. To assess protective effects of a vaccine against this strain, fish were injected with an inactivated vaccine (immunization group, IG) or 0.85% sterile saline (control group 2, CG2) for 28-day observation period, then challenged with JW-4 on the 28th day. The inactivated vaccine enhanced total and specific IgM to A. veronii levels of the fish, resulting in a relative percentage survival of 75% in IG. These findings provide a foundation for identifying pathogenic bacteria and developing more effective prophylactic strategies in aquaculture.

Dietary supplementation with polysaccharides from Rhizoma dioscoreae resulting in the enhanced immunity and the structural modulation of the intestinal microbiota in Luciobarbus capito

Rhizoma Dioscoreas (R. dioscoreae), also known as Chinese yam, is a well-known edible and pharmaceutical plant in China. Yam polysaccharide (YP) is one of the main bioactive components of R. dioscoreae due to its decent medicinal and nutritional value. However, the underlying effect of YP treatment on Luciobarbus capito (L. capito) still remains unknown. Considering this, the current work aims to investigate the potential impact of different levels of YP treatment (i.e. 0.10 g/L, 1.00 g/L and 10.0 g/L) on L. capito in the context of the antioxidant enzyme activity, immune-related enzyme activity, digestive enzyme activity and intestinal microbiota. The activities of most antioxidant enzymes and immune-related enzymes were found to be generally increased after the varied doses of YP treatment, particularly for CAT, ACP and AKP (P < 0.05). This indicated that YP treatment could enhance the antioxidant activity and immune functions of L. capito via the modulation of various metabolic enzymatic activities. 16S rRNA gene amplicon sequencing data revealed that YP treatment can trigger dramatical alterations in the compositional structures of the dominant intestinal microbiota in L.capito, which could significantly increase the relative abundance of Aeromonas and decrease the relative abundance of Lactobacillus and Cetobacterium (P < 0.05). The global diversity of the intestinal microbiota of L. capito after different levels of YP treatment was found to be generally decreased, particularly reduced after 1.00 g/L YP treatment (P < 0.05). Functional predications revealed that there were no significant differences within different functional categories, including Biosynthesis category, Degradation/Utilization/Assimilation category, and Generation of Precursor Metabolites and Energy category, among others (P > 0.05). This work would be helpful to uncover the potential effect of YP treatment on L. capito and provide further insights into future utilization of YP as supplement to ameliorate the immunity and modulate the intestinal microbiota during the aquaculture process of L. capito.

Dietary supplement of Antheraea pernyi cecropin enhances the growth rate and disease resistance of the Yesso scallop, Patinopecten yessoensis

A feeding trial was carried out for 30 days to investigate the impacts of dietary immunity induced A. pernyi pupae powder (IPP) and A. pernyi cecropin (AC) on the growth, immune-related enzyme activities and disease resistance in Yesso scallop, Patinopecten yessoensis. A total of 320 scallops, with an average weight of 54.75 ± 0.07 g were randomly divided into four treatment groups: control group (provided with a diet of spirulina powder and microalgae), groups with basic diet supplemented with A. pernyi pupae powder (NPP, 2 % of the final concentration), immunity induced A. pernyi pupae powder (IPP, 2 % of the final concentration), and A. pernyi cecropin (AC, 2 % of the final concentration), respectively. The results showed that the specific growth rate (SGR), lysozyme (LSZ), acid phosphatase (ACP) and superoxide dismutase (SOD) were significantly higher in the scallops fed with AC than in the other groups (P < 0.05). Unfortunately, NPP and IPP exhibited an inhibitory effect on SGR and all the detected immune index parameters of the scallops, whereas the activities of LSZ and SOD decreased significantly compared to those of the control group (P < 0.05). Disease resistance was significantly increased in the scallops treated with AC, recording the lowest mortality percentage of 43.3 % following a challenge with Vibrio chagasii (P = 0.0001). The results of the present study suggest that supplementing the diet with AC at 2 % can significantly enhance the weight gain rate, immunity and disease resistance of scallops.

Investigating the interplay between Cryptocaryon irritans ectoparasite infection and the immune responses of the head kidney in silver pomfret (Pampus argenteus)

Cryptocaryoniasis is one of the devastating protozoal diseases present in marine fish species, leading to high mortality in the fish aquaculture. Recently, white spot disease caused by Cryptocaryon irritans was found to infect the fins and skin of silver pomfret (Pampus argenteus). To better understand the innate immune effects underlying the host response against C. irritans, transcriptome analysis of head kidney (HK) in silver pomfret between non-infected group (sham control) and C. irritans infected was performed. In total, 5141, 3678, and 3895 differentially expressed genes (DEGs) were identified between the control and either 3, 7 or 14 days post infection (dpi), respectively. KEGG enrichment analysis results showed that C. irritans infection induced a complex immune response regulated by the cooperation of various immune related pathways, including ECM-receptor interactions, p53 signaling pathway, cytokine-cytokine receptor interaction, and Jak-STAT signaling pathway. Additionally, the histopathological structure of the HK underwent dynamic changes characterized by renal structure damage and focal necrosis throughout the course of the infection. Furthermore, the levels of the immune-related enzyme (LZM, SOD, ACP and AKP) activities were significantly increased at various time points after infection. Taken together, the findings of this study will not only provide novel insights into the essential first line defense mechanisms involved in the host-C. irritans interaction but also contribute to advance research efforts aimed at developing disease prevention strategies for silver pomfret aquaculture industry.

Transcriptome profiling and differential expression analysis of altered immune-related genes in goldfish (Carassius auratus) infected with Aeromonas hydrophila

Goldfish (Carassius auratus) have been employed as a model organism to investigate the innate immune system and host-pathogen interactions. A Gram-negative bacterium called Aeromonas hydrophila has been found to cause mass mortality due to infection in a wide variety of fish species in the aquatic system. In this study, damages in Bowman's capsule, inflammatory tubular (proximal and distilled convoluted) structure, and glomerular necrosis were observed in A. hydrophila-infected head kidney of goldfish. To increase the better understanding of immune mechanisms of host defense against A. hydrophila, we performed a transcriptome analysis in head kidney of goldfish at 3 and 7 days of post-infection (dpi). Comparing to the control group, 4638 and 2580 differentially expressed genes (DEGs) were observed at 3 and 7 dpi, respectively. The DEGs were subsequently enriched in multiple immune-related pathways including Protein processing in endoplasmic reticulum, Insulin signaling pathway, and NOD-like receptor signaling pathway. The expression profile of immune-related genes such as TRAIL, CCL19, VDJ recombination-activating protein 1-like, Rag-1, and STING was validated by qRT-PCR. Furthermore, the levels of immune-related enzyme (LZM, AKP, SOD, and CAT) activities were examined at 3 and 7 dpi. The knowledge gained from the current study will be helpful for better understanding of early immune response in goldfish after A. hydrophila challenge, which will aid in future research on prevention strategies in teleost.

Effects of the Exopolysaccharide from Lactiplantibacillus plantarum HMX2 on the Growth Performance, Immune Response, and Intestinal Microbiota of Juvenile Turbot, Scophthalmus maximus.

In this study, the exopolysaccharide (EPS) from Lactiplantibacillus plantarum (HMX2) was isolated from Chinese Northeast Sauerkraut. Its effects on juvenile turbot were investigated by adding different concentrations of HMX2-EPS (C: 0 mg/kg, H1: 100 mg/kg, H2: 500 mg/kg) to the feed. Compared with the control group, HMX2-EPS significantly improved the growth performance of juvenile turbot. The activities of antioxidant enzymes, digestive enzymes, and immune-related enzymes were significantly increased. HMX2-EPS could also increase the secretion of inflammatory factors and enhance the immune response of turbot by regulating the IFN signal transduction pathway and exhibit stronger survival rates after the A. hydrophila challenge. Moreover, HMX2-EPS could improve the diversity of intestinal microbiota in juvenile fish, increase the abundance of potential probiotics, and reduce the abundance of pathogenic bacteria. The function of gut microbes in metabolism and the immune system could also be improved. All results showed better effects with high concentrations of HMX2-EPS. These results indicated that HMX2-EPS supplementation in the diet could promote growth, improve antioxidant activity, digestive capacity, and immunity capacity, and actively regulate the intestinal microbiota of juvenile turbot. In conclusion, this study might provide basic technical and scientific support for the application of L. plantarum in aquatic feed.