Aeromonas Hydrophila Challenge Research Articles

Different response of Acipenser gueldenstaedtii CRP/SAP and SAA to bacterial challenge and chronic thermal stress sheds light on the innate immune system of sturgeons

Sturgeons are chondrostean fish critically endangered due to anthropogenic loss and degradation of natural habitat and overfishing for meat and caviar production. Consequently, sturgeon aquaculture has extensively developed lately, being Russian sturgeon (Acipenser gueldenstaedtii) the second most important species reared for caviar production. However, Russian sturgeon aquaculture in subtropical countries, such as Uruguay, confronts difficulties because fish have to endure excessive summertime warm temperatures, which weaken their innate defences facilitating opportunistic infections. To address this problem, we look for identifying putative acute phase proteins (APPs), which might be robust serum biomarkers of both infection and chronic thermal stress, applied to monitoring Russian sturgeon health status in farms. We focused on the C-Reactive Protein/Serum Amyloid P (CRP/SAP) pentraxin since the pentraxin family includes well-known APPs, better characterised in mammals than fish. We identified A.gueldenstaedtii CRP/SAP (AgCRP/SAP), as a member of the universal CRP/SAP pentraxin sub-family, and studied AgCRP/SAP involvement in sturgeon response to bacterial challenge and chronic thermal stress, in comparison with A. gueldenstaedtii Serum Amyloid A (AgSAA), a previously described positive APP. Results showed that AgCRP/SAP is a constitutive serum component that remained constant upon Aeromonas hydrophila challenge and chronic thermal stress. Contrastingly, serum AgSAA was subjected to regulation by bacterial and thermal stress challenges, showing a 50-fold increase and 3-fold decline in serum levels, respectively. Overall, results highlight the potential value of AgSAA, but not of AgCRP/SAP, as a biomarker of bacterial infection and the need to continue searching for robust chronic thermal stress biomarkers in sturgeons.

Evaluation of dietary genistein on the antioxidant capacity, non-specific immune status, and fatty acid composition of common carp (Cyprinus carpio .L)

This experiment was performed to determine the effect of dietary genistein on the growth, antioxidation, immunity, as well as lipid metabolism of common carp (Cyprinus carpio.L). Six experimental feeds containing 0 (control group), 25, 50, 100, 500 or 1000 mg/kg of genistein were respectively formulated. The feeds were randomly assigned to triplicate tanks with 30 fish (initial weight (20.59 ± 0.69) g) for 8 weeks. All the growth parameters were significantly improved by supplementation with 100 and 500 mg/kg genistein. The alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were reduced, but the acid phosphatase (ACP) activity was increased in serum of the 100 mg/kg genistein group. The total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) levels were significantly increased in serum when the feed was supplemented with 500 mg/kg of genistein. The total cholesterol (TC), triglyceride (TG), and low–-density lipoprotein cholesterol (LDL-C) levels in serum were reduced in the genistein (100 and 500 mg/kg) supplement groups. The mRNA expression levels of the pro-inflammatory cytokines, such as interleukin 1 (il-1), the nuclear factor kb (nf-kb), and il-8 were reduced, but the expressions of anti-inflammatory cytokines, such as transforming growth factor-b (tgf-b) and il-10 were enhanced in the head kidney and spleen tissues after genistein supplementation. Furthermore, the immune enhancement of genistein was confirmed by increasing the survival rate of common carp to Aeromonas hydrophila challenge. In addition, the fatty acids profile in the liver and muscle of common carp indicated that an increase of muscle total PUFA, especially n-3 PUFA and HUFA levels in 100 or 500 mg/kg genistein supplement groups. Meanwhile, after the feeding trial, the amount of total PUFA in the liver was significantly elevated in the 500 mg/kg genistein group. As the acsl6 and elovl5 mRNA expressions in the liver were enhanced after genistein treatment, the biosynthesis ability of endogenous HUFA may be enhanced. Moreover, lipogenesis-related genes in the liver were down-regulated after genistein treatment. Therefore, 100 and 500 mg/kg of genistein can significantly improve growth, body composition and lipid metabolism, enhance the antioxidant and immunity of common carp.

Effect of Pandanus tectorius extract as food additive on oxidative stress, immune status, and disease resistance in Cyprinus carpio

The present study investigated the effect of Pandanus tectorius (PT) extract on Cyprinus carpio growth, antioxidant capacity, immunological and oxidative stress, immune-related gene expression, and resistance against pathogen challenge. Fish (average weight: 12.18 ± 0.32 g) were fed with diets containing various concentration (g kg−1) of PT extract: 0 g (basal diet), 5 g [PT5], 10 g [PT10], 20 g [PT20], and 30 g [PT30] for 8 weeks. Our results revealed an increase (p < 0.05) in the final weight gain only in the PT20 (63.12 ± 1.4 g) group. Activity of liver antioxidant parameters such as catalase (CAT) (27.67 ± 1.12 U mg protein−1), superoxide dismutase (SOD) (13.17 ± 0.428 U mg protein−1), and glutathione peroxidase (GPx) (47.14 ± 1.47 U mg protein−1) was highest in the PT20 group. Among the serum immunological parameters examined, lysozyme (37.45 ± 0.67 U mL−1), alternative complement pathway (133.22 ± 1.92 U mL−1), and phagocytic activities (25.68 ± 0.93%) were high (p < 0.05) in PT20, whereas there was no significant effect on serum immunoglobulin or total protein levels, compared to the control. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and malondialdehyde (MDA) levels were found to be lower (p < 0.05) in the PT20 and PT30 groups than those in the control. However, myeloperoxidase (MPO) levels were significantly higher (p < 0.05) in the PT20 and PT30 groups. Gene expression analysis revealed that mRNA expressions of antioxidant genes (SOD, CAT, nuclear factor erythroid 2-related factor 2) and anti-inflammatory cytokine (IL-10) genes were significantly upregulated in the PT10 – PT30 groups, except for the SOD gene in PT10. Conversely, the signalling molecule NF-κBp65 was downregulated in PT20 and PT30. Expression of Toll-like receptor 22 (TLR22) and hepcidin was significantly upregulated in PT20 and PT30, respectively. Fish in the PT20 group exhibited highest relative post-challenge survival (70.37%) against Aeromonas hydrophila challenge. The results of the present study suggest that dietary supplementation of P. tectorius extract at 20 g kg−1 can significantly improve weight gain, serum antioxidant parameters, strengthen immunity, and increase the disease resistance of C. carpio. Therefore, P. tectorius extract could be exploited for its use as a food additive in aquaculture.

Mannan Oligosaccharides Application: Multipath Restriction From Aeromonas hydrophila Infection in the Skin Barrier of Grass Carp (Ctenopharyngodon idella).

The objective of this study was to evaluate the efficacy of dietary Mannan oligosaccharides (MOS) supplementation on skin barrier function and the mechanism of on-growing grass carp (Ctenopharyngodon idella). Five hundred forty grass carp were fed for 60 days from the growing stage with six different levels of MOS diets (0, 200, 400, 600, 800, and 1,000 mg kg-1). At the end of the growth trial, the 14-day Aeromonas hydrophila challenge experiment has proceeded. The obtained data indicate that MOS could (1) decline skin lesion morbidity after being challenged by the pathogenic bacteria; (2) maintain physical barrier function via improving antioxidant ability, inhibiting excessive apoptosis, and strengthening the tight junction between the epithelial cell and the related signaling pathway (Nrf2/Keap1, p38MAPK, and MLCK); and (3) regulate immune barrier function by modulating the production of antimicrobial compound and expression of involved cytokines and the related signaling pathway (TOR and NFκB). Finally, we concluded that MOS supplementation reinforced the disease resistance and protected the fish skin barrier function from Aeromonas hydrophila infection.

Comparative analysis of erythrocyte hemolysis, plasma parameters and metabolic features in red crucian carp (Carassius auratus red var) and triploid hybrid fish following Aeromonas hydrophila challenge

Aeromonas hydrophila can pose a great threat to survival of freshwater fish. In this study, A. hydrophila challenge could promote the erythrocyte hemolysis, increase free hemoglobin (FHB) level and generate malondialdehyde (MDA) production in plasma but decrease the levels of total antioxidant capacity (T-AOC), total superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (ALP) and lysozyme (LZM) of red crucian carp (RCC, 2 N = 100) and triploid hybrid fish (3 N fish, 3 N = 150) following A. hydrophila challenge. Elevated expression levels of heat shock protein 90 alpha (HSP90α), matrix metalloproteinase 9 (MMP-9), free fatty acid receptor 3 (FFAR3), paraoxonase 2 (PON2) and cytosolic phospholipase A2 (cPLA2) were observed in A. hydrophila-infected fish. In addition, A. hydrophila challenge could significantly increase expressions of cortisol, leucine, isoleucine, glutamate and polyunsaturated fatty acids (PUFAs) in RCC and 3 N, while glycolysis and tricarboxylic acid cycle appeared to be inactive. We identified differential fatty acid derivatives and their metabolic networks as crucial biomarkers from metabolic profiles of different ploidy cyprinid fish subjected to A. hydrophila infection. These results highlighted the comparative metabolic strategy of different ploidy cyprinid fish against bacterial infection.

An IL-1β homologue induced inflammation and antibacterial immune defense in Siberian sturgeon (Acipenser baeri)

Interleukin-1β is a key pro-inflammatory cytokine functioning in initiation of inflammatory responses against bacterial- and viral-infections. In the present study, a putative IL-1β counterpart was identified from Siberian sturgeon (Acipenser baeri) and designated as AbIL-1β. The Abil-1β cDNA sequence consists of 1130 bp with an open reading frame (ORF) of 585 bp, which encodes a 194 amino acid (aa) protein. Multiple amino acid sequence alignment revealed that a possible mature peptide could start at Leu18, although no cut site for ICE (IL-1β converting enzyme) enzyme was present in Siberian sturgeon IL-1β. Even if AbIL-1β shares a relative low identity (33.6%) with another sturgeon type II IL-1β gene from Acipenser dabryanus, they still clustered together in phylogenetic tree. Endogenous Abil-1β was highly expressed in brain, blood, head kidney and spleen of healthy Siberian sturgeon, and remarkably up regulated in head kidney, spleen, and liver upon Aeromonas hydrophila (A.h) challenge. Consistently, in vitro stimulation test using heat-killed A.h and LPS significantly increased Abil-1β transcripts of primary spleen cells. To investigate the bactericidal capability of AbIL-1β, recombinant AbIL-1β (rAbIL-1β) was generated by prokaryotes. Pre-injection of rAbIL-1β reduced the bacterial load in sturgeon spleen after A.h infection. Further, rAbIL-1β was served as feed additive and demonstrated to enhance hybrid sturgeon's defense against A.h infection by increased expressional levels of immune-related genes (IL-1β, IL-6, IL-8, IgM and MHCIIβ), elevated activities of serum lysosome, ACH50, and MPO, as well as higher percent survival. In summary, the current results suggested that AbIL-1β functions in immune regulation and could improve sturgeon's resistance to bacterial infection.

40S ribosomal protein S18 is a novel maternal peptidoglycan-binding protein that protects embryos of zebrafish from bacterial infections

Previous studies have shown that ribosomal proteins play important roles in ribosome assembly and protein translation, but other biological functions remain ill-defined. Here it is clearly demonstrated that RPS18 is a newly identified PGN-binding protein which is present abundantly in the eggs/embryos of zebrafish. Recombinant RPS18 not only identifies the bacterial signature molecule PGN, LPS, and LTA, and binds the bacteria as a pattern recognition receptor, but also kills the Gram-positive and Gram-negative bacteria as an antibacterial effector molecule. What is important is that, we reveal that microinjection of rRPS18 into early embryos significantly improved the resistance of the embryos against pathogenic Aeromonas hydrophila challenge, and co-injection of anti-RPS18 antibody could markedly reduced this improved bacterial resistance. In summary, these results indicate that RPS18 is a maternal immune factor that can protect the early embryos of zebrafish against pathogenic attacks. This work also provides another angle for understanding the biological functions of ribosomal proteins.

Functional and Stress Response Analysis of Heat Shock Proteins 40 and 90 of Giant River Prawn (Macrobrachium rosenbergii) under Temperature and Pathogenic Bacterial Exposure Stimuli.

The aims of this research were to perform molecular characterization and biofunctional analyses of giant river prawn Hsp40 and Hsp90 genes (Mr-hsp40 and Mr-hsp90) under various stress conditions. Comparisons of the nucleotide and amino acid sequences of Mr-hsp40 and Mr-hsp90 with those of other species showed the highest similarity scores with crustaceans. Under normal conditions, expression analysis using quantitative real-time RT-PCR (qRT-PCR) indicated that Mr-hsp40 was highly expressed in the gills and testis, and Mr-hsp90 expression was observed in all tissues, with the highest expression in the ovary. The expression patterns of Mr-hsp40 and Mr-hsp90 transcripts under Aeromonas hydrophila challenge and heat–cold shock conditions were examined in gills, the hepatopancreas and hemocytes, at 0, 3, 6, 12, 24, 48 and 96 h by qRT-PCR. Under bacterial challenge, Mr-hsp40 displayed variable expression patterns in all tissues examined during the tested periods. In contrast, upregulated expression of Mr-hsp90 was quickly observed from 3 to 12 h in the gills and hepatopancreas, whereas obviously significant upregulation of Mr-hsp90 was observed in hemocytes at 12–96 h. Under temperature shock conditions, upregulation of Mr-hsp40 expression was detected in all tested tissues, while Mr-hsp90 expression was quickly upregulated at 3–48 h in all tissues in response to 35 °C conditions, and conditions of 35 and 25 °C stimulated its expression in gills and the hepatopancreas at 12 and 48 h, respectively. Silencing analyses of these two genes were successfully conducted under normal, high-temperature (35 °C) and A. hydrophila infection conditions. Overall, knockdown of Mr-hsp40 and Mr-hsp90 effectively induced more rapid and higher mortality than in the PBS control and GFP induction groups in temperature and infectious treatments. Evidence from this study clearly demonstrated the significant functional roles of Mr-hsp40 and Mr-hsp90, which are crucially involved in cellular stress responses to both temperature and pathogenic bacterial stimuli.

A liquid seaweed extract (TAM®) improves aqueous rearing environment, diversity of zooplankton community, whilst enhancing growth and immune response of Nile tilapia, Oreochromis niloticus, challenged by Aeromonas hydrophila

A commercial seaweed liquid extract (TrueAlgaeMax, TAM®), previously showed a high content of phytochemical compounds and resulted in promoting growth and immune response of Nile tilapia, when applied as dietary supplementation. In the current study, the effects of applying TAM® as a natural agent to rearing water on growth performance, feed utilization, and immune response of Nile tilapia, Oreochromis niloticus, challenged by Aeromonas hydrophila were conducted. Also, zooplankton community, diversity, and abundance were evaluated in the cultured water. Five experimental groups (G0, G1, G2, G3, and G4) were exposed to different TAM® concentrations (0, 50, 100, 150, and 200 ml m‐3 of culture water, respectively). Healthy 450 mono-sex O. niloticus fingerlings (26.048 ± 0.050 g) were randomly stocked in glass aquariums (150 L aquaria−1, thee replicates treatment−1). The water in aquariums was renewed with a rate of 10% every 4 days and supplied with new freshwater with maintaining the respect TAM® concentrations. The feces and uneaten food were daily removed. The fish were fed at a level of 3% of body weight during the 70-days experimental period. The results revealed that TAM® exposed groups yielded higher significant growth performance, feed intake, and feed utilization compared to the control group. The non-specific immune response (total protein, albumin, globulin levels, and lysozyme activity) and antioxidant enzyme activities were significantly improved with increasing TAM® exposure levels. The resistance of O. niloticus against Aeromonas hydrophila challenge improved significantly in different TAM® treatments. Comparing to the control, TAM® treatments improved the zooplankton community, diversity, and abundance. Due to TAM® photobiotic, applying TAM® levels (especially G4) are significantly flourishing the abundance of Rotifera and Polychaeta, while, inhibiting the abundance of Nematoda, Trematoda, and Insecta. Finally, it can be concluded that the aqueous exposure to seaweed extract TAM® could improve fish growth performance, health status, and resistance against pathogenic bacteria challenge. In addition, it has a desirable modulation effect on natural microbiota in the fish rearing water.

Tributyrin Plays an Important Role in Regulating the Growth and Health Status of Juvenile Blunt Snout Bream (Megalobrama amblycephala), as Evidenced by Pathological Examination

The present study aimed to assess the role of tributyrin (TB) in regulating the growth and health status of juvenile blunt snout bream (Megalobrama amblycephala) through an 8-week feeding experiment. Six groups were fed experimental diets with added TB percentages of 0% (control group), 0.03%, 0.06%, 0.09%, 0.12% and 0.15%. The present results showed that TB supplementation in feed had some positive impacts on FW, WG, FCR and SGR, and the best results were found in the 0.06% TB group (P<0.05). However, TB supplementation in feed had no significant effects on SR, CF, VSI or whole-body composition (P>0.05). TB supplementation in feed increased antioxidant capacity and immunological capacity and attenuated the inflammatory response by increasing the activity of T-SOD, GPx, CAT and the levels of anti-inflammatory cytokines (IL-10 and TGF-β) and decreasing the levels of MDA and anti-inflammatory cytokines (TNF-α) (P<0.05). Furthermore, TB supplementation improved immunity by increasing the levels of immunoglobulins (IgM and IgG), C3 and IFN-γ (P<0.05). Surprisingly, 0.06%-0.12% TB supplementation significantly increased the content of IL-1β (P<0.05). However, TB supplementation in feed had no significant effects on the plasma content of GSH, HSP70, IL-8 and the activity of T-AOC (P>0.05). The possible mechanism was that TB activated PI3K/Akt/Nrf2 and inhibits the NF-κB signaling pathway, further regulating the mRNA levels of key genes with antioxidant capacity and the inflammatory response; for example, it increased the mRNA levels of Nrf2, Cu/Zn-SOD, HO-1, CAT, Akt, PI3K, GPx, IL-10, and TGF-β and decreased the mRNA levels of NF-κB and TNF-α (P<0.05). In addition, 0.06%-0.15% TB supplementation significantly increased the mRNA levels of IL-1β (P<0.05). TB supplementation in feed had no significant effects on the mRNA levels of HSP70, Mn-SOD and IL-8 (P>0.05). Evidence was presented that TB supplementation decreased the mortality rate caused by Aeromonas hydrophila challenge. In pathological examination, TB supplementation prevented hepatic and intestinal damage. Generally, TB supplementation improved the growth performance of juvenile blunt snout bream. Furthermore, TB supplementation activated PI3K/Akt/Nrf2 and inhibited the NF-κB signaling pathway, regulating health status and preventing hepatic and intestinal damage.

Immune response and susceptibility of Nile tilapia fish to Aeromonas hydrophila infection following the exposure to Bifenthrin and/or supplementation with Petroselinum crispum essential oil

Bifenthrin (BF) is a widely used 3rd generation type I pyrethroid with a potential toxic effect in fish. Nevertheless, its effect on the immune system remains unclear. In the present study, Oreochromis niloticus was exposed to BF at 0.68 μg/L for 60 days, followed by evaluating the hematological, biochemical, and immunological responses. Additionally, the potential of parsley (Petroselinum crispum) essential oil (PEO) to ameliorate the BF-induced toxic insults was explored. Our data have shown reductions in the growth performance with alterations observed in the hematological variables, protein profile and serum biomarkers of stress. DNA oxidative damage was evidenced by elevation of serum 8-hydroxy-2-deoxyguanosine (8-OHdG) content. BF-exposed fish presented also decline in serum lysozyme activity and levels of immunoglobulins (IgG and IgM) and nitric oxide (NO), with diminished resistance to Aeromonas hydrophila challenge. Furthermore, the RT-PCR analysis showed an upregulated expression pattern of immune –related genes including interleukin 1β (IL-1β), interferon - γ (IFN-γ) and tumor necrosis factor - α (TNF-α) genes in the liver tissue. Dietary co-supplementation of PEO at 1 or 2 mL/kg diet with concomitant BF exposure, alleviated the adverse effects of the insecticide in a dose-dependent manner. The observations from this study demonstrate the immunomodulation by BF and provide further insight into the protective properties of PEO and strengthen its applicability as a promising feed supplement to fish.

Utilization of pelleted and extruded feed by blunt snout bream Megalobrama amblycephala: Insights from growth performance, health status and feed cost.

The present study was conducted to evaluate the utilization of both pelleted feed (PF) and extruded feed (EF) by blunt snout bream Megalobrama amblycephala based on growth performance, stress responses, innate immunity and disease resistance. Both the PF and EF were prepared with the same formula. Fish were divided randomly into 2 groups, including one fed the PF continuously and one offered the EF continuously. The whole feeding trial lasted 8weeks, after which fish were subjected to Aeromonas hydrophila infection. The results showed that the feed intake, feed conversion ratio, hepatic total superoxide dismutase activity and glutathione content, plasma complement 3 and complement 4 levels as well as myeloperoxidase activity of the EF group were all significantly lower than those of the PF group, while the opposite was true for the condition factor, the viscera index, the abdominal fat percentage, nitrogen and energy retention, hepatic malondialdehyde content, plasma levels of cortisol, glucose, lactate, total protein and globulin as well as the activities of plasma alanine aminotransferase and aspartate aminotransferase. In addition, the EF group also obtained relatively low activities of hepatic glutathione peroxidase and plasma acid phosphatase as well as high cumulative mortality rates at 24-96h after Aeromonas hydrophila challenge. Furthermore, the feed cost of culturing this species with EF is lower than that with PF. These findings indicated that compared with PF, EF could increase the feed utilization and economic benefits of blunt snout bream, but reduce its anti-stress ability, non-specific immunity, A. hydrophila resistance and feed cost.

ELAVL1a is an immunocompetent protein that protects zebrafish embryos from bacterial infection

Previous studies have shown that ELAVL1 plays multiple roles, but its overall biological function remains ill-defined. Here we clearly demonstrated that zebrafish ELAVL1a was a lipoteichoic acid (LTA)- and LPS-binding protein abundantly stored in the eggs/embryos of zebrafish. ELAVL1a acted not only as a pattern recognition receptor, capable of identifying LTA and LPS, as well as bacteria, but also as an effector molecule, capable of inhibiting the growth of Gram-positive and -negative bacteria. Furthermore, we reveal that the C-terminal 62 residues of ELAVL1a positioned at 181–242 were indispensable for ELAVL1a antibacterial activity. Additionally, site-directed mutagenesis revealed that the hydrophobic residues Val192/Ile193, as well as the positively charged residues Arg203/Arg204, were the functional determinants contributing to the antimicrobial activity of rELAVL1a. Importantly, microinjection of rELAVL1a into embryos markedly promoted their resistance against pathogenic Aeromonas hydrophila challenge, and this pathogen-resistant activity was considerably reduced by co-injection of anti-ELAVL1a antibody or by knockdown with morpholino for elavl1a. Collectively, our results indicate that ELAVL1a is a maternal immune factor that can protect zebrafish embryos from bacterial infection. This work also provides another angle for understanding the biological roles of ELAVL1a.

Oregano (Origanum vulgare) Extract Enhances Zebrafish (Danio rerio) Growth Performance, Serum and Mucus Innate Immune Responses and Resistance against Aeromonas hydrophila Challenge.

Simple SummaryThere has been extensive research addressing the positive effects of medicinal plant extracts using food fish as animal models. The present research was an attempt to assess zebrafish viability, considering the 3Rs approach, as an animal model for dietary experiments for fish nutrition studies, particularly evaluating novel additives for further implications in food fish. We have found oregano (Origanum vulgare) extract to be remarkably effective on fish growth and the fish immune system, enabling fish to fight a bacterial invasion. This study evaluated the dietary effects of an ultrasound-assisted extract of Origanum vulgare on the growth, antioxidant and immune responses (serum and mucosal) and resistance of zebrafish (Danio rerio) against Aeromonas hydrophila. Four hundred and forty adult zebrafish were distributed into 12 tanks and fed 4 experimental diets including 0% (control), 0.5% (M1), 1% (M2) and 2% (M3) of the extract per kg−1 diet for eight weeks. Fish were then challenged with A. hydrophila and mortality was recorded for 10 days. Results revealed that the extract exerted potent effects on growth parameters of weight gain and specific growth rate. The feed conversion ratio was significantly lower in fish fed extract-incorporated diets. O. vulgare extract improved antioxidant and immune responses, resulting in less sensitivity to oxidative stress and a higher survival rate when challenged with A. hydrophila. Overall, the greatest effects were observed in individuals with 1% dietary inclusion of the extract. These results suggest that the extract from the plant Origanum vulgare possesses a great potential to be used in the aquaculture industry and that zebrafish is an appropriate model for nutrition studies.

Effects of dietary xylooligosaccharide on growth performance, enzyme activity and immunity of juvenile grass carp, Ctenopharyngodon idellus

An 8-week feeding trial was conducted to evaluate the effects of xylooligosaccharde (XOS) on growth, immunity and disease resistance of juvenile grass carp (Ctenopharyngodon idella). Fish (3.05 ± 0.01 g) were fed with diets containing XOS at levels of 0, 0.05 %, 0.1 %, 0.2 %, 0.4 % and 0.6 %. Results showed that the plasma triglyceride content was significantly lower in fish fed dietary 0.05 % and 0.1 % XOS compared to the control group (P < 0.05). Fish fed dietary 0.05 %, 0.1 % and 0.2 % XOS displayed significantly higher final body weight, weight gain and specific growth rate compared to the control group (P < 0.05). Fish fed 0.1 % XOS had significantly lower plasma malondialdehyde content and higher lysozyme activity than the control group (P < 0.05). XOS did not affect liver superoxide dismutase activity and glutathione content, but significantly reduced MDA content (0.4 % and 0.6 %) (P < 0.05). After Aeromonas hydrophila challenge, 0.1 % XOS significantly improved the survival rate of C. idella compared to that of the control diet (P < 0.05). Thus, the most suitable dietary supplementation level of XOS is 0.1 % for C. idella.

The potential benefits of dietary β‐glucan against growth retardation, immunosuppression, oxidative stress and expression of related genes and susceptibility to Aeromonas hydrophila challenge in Oreochromis niloticus induced by herbicide pendimethalin

The present analysis aimed to assess the immunomodulation effects of β-glucan (βG) against the sub-lethal concentrations of herbicide pendimethalin (PMN). 360 Oreochromis niloticus fingerlings were randomly classed into four groups. The control one (CON) was fed on basal diet. βG group was fed on the basal diet accompanied with 0.5 βG g/kg−1. The PMN group was endangered to PMN at a dosage of 0.52 mg/L. βG/PMN group was supplemented with combination of βG and exposed to PMN as beforehand stated for eight weeks. Stunting of the growth parameters followed PMN was improved by βG. PMN revealed a significant decline in total number of leucocytes. Furthermore, reduced in immunoglobulin M (IgM), lysozymes, superoxide dismutase (SOD) and catalase (CAT), likewise, increased in malondialdehyde (MDA), cortisol, hepatic and renal markers by exposure to PMN. Also, PMN revealed up-regulation of mRNA levels of IgM in the spleen. Conversely, the expression of CAT, SOD and il8 was down-regulated. PMN increased the sensibility to Aeromonas hydrophila challenge, manifested by a significantly increased of cumulative mortality post challenge. The mortalities have been stopped at the 7, 8, 11 and 12th days in, βG, CON, βG/PMN and PMN respectively. Our results accomplish that PMN influences immune responses and antioxidant balance by the adverse transcriptional impact on genes concerned in immunity and also inflammatory indicators on immune organs. In addition, supplementation with βG could be beneficial for alleviates of the immunity in response to PMN exposure.

Ameliorating deleterious effects of high stocking density on Oreochromis niloticus using natural and biological feed additives

The current study was conducted to investigate the stress effect of high stocking density and to evaluate the efficiency of Glycyrrhiza glabra extract (LE) and protexin concentrate (PC) in Oreochromis niloticus. A total of 360 Nile tilapia fingerlings were divided into 5 groups. The 1st and the 2nd groups were stocked at a rate of 10 fish/aquarium (control) and 20 fish/aquarium (HSD), respectively. The 3rd group (20 fish/aquarium fed on basal diet supplemented with 200 mg/kg protexin) (HSD + PC). The 4th group (20 fish/aquarium fed on basal diet supplemented with 500 mg/kg LE) (HSD + LE). The 5th group (20 fish/aquarium fed on basal diet supplemented with 200 mg/kg PC+ 500 mg/kg LE) (HSD + PC + LE). HSD group had the lowest body weight, specific growth rate and feed intake. After the Aeromonas hydrophila challenge, fishes from HSD recorded the highest mortality, while the opposite occurred in supplemented groups. It could be concluded that supplementation of LE, PC separately or in combination can positively attenuate the undesirable effects of HSD on growth, antioxidant, immunity and bacterial disease resistance of fish.

Molecular cloning, characterization of JunB in Schizothorax prenanti and its roles in responding to Aeromonas hydrophila infection

The transcription factor JunB can induce physiological or pathological responses to various stimuli, including immune stimulants and bacteria, and plays an important role in the immune response process. In this study, we identified a JunB family member in Schizothorax prenanti (S. prenanti), which was designated SpJunB. The complete coding sequence (CDS) of SpJunB was 930 bp in length, which was submitted to GenBank (ID: MN215886). SpJunB encodes a putative protein of 309 amino acids, which is highly homologous to JunB of common carp. The SpJunB protein contained a conserved JunB domain, and its 3D structure was also highly similar to (77.61%) the human SpJunB protein. SpJunB was found to be extensively expressed in various tissues, with the highest expression in the spleen. The expression of SpJunB was significantly upregulated after Aeromonas hydrophila (A. hydrophila) challenge. Prokaryotic expression indicated that a 51 kDa recombinant protein was obtained after induction with 1.5 mmol/L isopropyl-beta-D-thiogalactopyranoside (IPTG) for 6 h at 37 °C. The expression levels of IL-1β, IL-6 and IL-8 were significantly upregulated (p < 0.01) after treatment of S. prenanti with the SpJunB protein. The activities of SOD, AKP and LZM were also significantly increased (p < 0.01) after the treatment of S. prenanti with the SpJunB protein. Simultaneously, the SpJunB protein reduced the infection rate of A. hydrophila in S. prenanti. In conclusion, SpJunB may improve the immune functions of S. prenanti. It will be beneficial to further study the immune mechanism of JunB in fish.

A novel biomarker for marine environmental pollution: A metallothionein from Mytilus coruscus

As one of the key enzymes that maintain the dynamic balance of metal content in animals and take part in the process of heavy metals detoxification, metallothionein (MT) is also associated with the process of immune response. In this study, the full-length metallothionein cDNA sequence of 324 bp from Mytilus coruscus was obtained (named as McMT) with a 222bp ORF encoding 73 amino acid residues in length and its theoretical pI/MW was 7.75/7.21 kDa. Blastp showed that the deduced amino acid sequence of McMT had significant homology with metallothionein from many animals, plants and bacteria, especially with other known MT of mollusca, for example Mytilus edulis and Mytilus galloprovincialis and they fell into the same evolutionary branch. Real-time PCR was used to examine the transcript pattern of McMT in hemocyte, gill, hepatopancreas, gonad, adductor and mantle. The highest transcript level appeared in hepatopancreas, which showed its multiple physiological roles with relation to the tissue type and the maximum expression in hepatopancreas could contribute to detoxification. Under the stress of heavy metal exposure for 15 days, the time-dependent expression pattern of McMT was observed in each treated group, but the highest expression appeared at different times for various concentrations of Cu2+ and Pb2+. The temporal expression of McMT after bacteria (Vibrio parahemolyticus and Aeromonas hydrophila) challenge firstly rose and then went down, and the expression peak appeared at 4h after V.parahemolyticus infection with 40-fold and 100-fold under A.hydrophila stress at 24h. The results suggested that McMT played a significant role in antioxidation and the expression of McMT can be used as a biomarker for monitoring the situation of marine pollution.

Functional characterization of an immunity-related GTPase gene in immune defense from obscure puffer (Takifugu obscurus)

Immunity-related GTPases (IRGs) are a family of large interferon-inducible GTPases that function in effective host defense against invading pathogens. IRGs have been extensively studied in mammals for their roles in the elimination of intracellular pathogens; however, their homologs in lower vertebrates are not well known. In this study, an IRG from obscure puffer (Takifugu obscurus), ToIRG, was identified and further characterized for its functional activity. The ToIRG gene encodes a protein of 396 amino acids containing a typical N-terminal GTPase domain with three conserved motifs. Phylogenetic analysis revealed that it has a closer evolutionary relationship with mammalian GKS IRGs. Gene expression profile analysis revealed that ToIRG was ubiquitously expressed in all tested healthy tissues of obscure puffer and upregulated in response to Aeromonas hydrophila or Edwardsiella tarda challenge. The subcellular localization of ToIRG is characterized as condensed forms around the nucleus. Importantly, an antimicrobial assay in vitro suggested that ToIRG enhanced the ability of host cells to resist both intracellular (E. tarda) and extracellular pathogens (A. hydrophila). Taken together, these results provide the functional characterization of obscure puffer IRGs in immune defense, which is the first study to reveal the function of IRGs in bony fish and will provide important insights into the evolutionary divergence of IRGs.