Disease Control In Aquaculture Research Articles

Area management strategies for disease control in aquaculture: Perspectives on infectious salmon anemia (ISA) spread from two continents

Area management strategies for disease control in aquaculture: Perspectives on infectious salmon anemia (ISA) spread from two continents

A potential application of shrimp antilipopolysaccharide factor in disease control in aquaculture

Antilipopolysaccharide factor isoform 3 from Penaeus monodon (ALFPm3) exhibits broad antimicrobial activities against various microbes, including bacteria, fungi and viruses, suggesting its potential use in disease control in shrimp aquaculture. Herein, the recombinant ALFPm3 protein (rALFPm3) exhibited effective antibacterial action against Vibrio parahaemolyticus, the causative agent of the new severe emerging disease, early mortality syndrome (EMS) or acute hepatopancreatic necrosis disease (AHPND) at the minimum inhibitory concentration value of 1.25–5.00 μM. The morphological changes such as bleb formation and cell distortion of V. parahaemoluticus were introduced after rALFPm3 treatment. Furthermore, to control V. parahaemoluticus infection, shrimp were treated with rALFPm3 by immersion and reduction in the cumulative mortality of V. parahaemoluticus-infected Penaeus vannamei was observed. As a potential immunostimulant, the administration of dietary rALFPm3 enhanced the transcript level of five immune-related genes; ALFPm3, haemocyte homoeostasis-associated protein, phagocytosis-activating protein, prophenoloxidase-activating enzyme 1 and cytosolic manganese superoxide dismutase. In addition, dietary rALFPm3 increased the shrimp survival after white spot syndrome virus (WSSV) injection by >35% compared to the 0% survival for the control group. Taken together, these results indicate the potential use of dietary rALFPm3 as immunostimulant in controlling AHPND and WSSV infections in shrimp aquaculture.

Review of the RNA Interference Pathway in Molluscs Including Some Possibilities for Use in Bivalves in Aquaculture

Generalised reviews of RNA interference (RNAi) in invertebrates, and for use in aquaculture, have taken for granted that RNAi pathways operate in molluscs, but inspection of such reviews show little specific evidence of such activity in molluscs. This review was to understand what specific research had been conducted on RNAi in molluscs, particularly with regard to aquaculture. There were questions of whether RNAi in molluscs functions similarly to the paradigm established for most eukaryotes or, alternatively, was it more similar to the ecdozoa and how RNAi may relate to disease control in aquaculture? RNAi in molluscs appears to have been only investigated in about 14 species, mostly as a gene silencing phenomenon. We can infer that microRNAs including let-7 are functional in molluscs. The genes/proteins involved in the actual RNAi pathways have only been rudimentarily investigated, so how homologous the genes and proteins are to other metazoa is unknown. Furthermore, how many different genes for each activity in the RNAi pathway are also unknown? The cephalopods have been greatly overlooked with only a single RNAi gene-silencing study found. The long dsRNA-linked interferon pathways seem to be present in molluscs, unlike some other invertebrates and could be used to reduce disease states in aquaculture. In particular, interferon regulatory factor genes have been found in molluscs of aquacultural importance such as Crassostrea, Mytilus, Pinctada and Haliotis. Two possible aquaculture scenarios are discussed, zoonotic norovirus and ostreid herpesvirus 1 to illustrate the possibilities. The entire field of RNAi in molluscs looks ripe for scientific exploitation and practical application.

Evaluation of Enterococcus spp. from rainbow trout (Oncorhynchus mykiss, Walbaum), feed, and rearing environment against fish pathogens.

The use of lactic acid bacteria of aquatic origin as probiotics constitutes an alternative strategy to the antibiotic treatment for disease control in aquaculture. Enterococci are currently used as probiotics in human and animal health. In this study, we evaluated the safety of 64 enterococci isolated from rainbow trout (Oncorhynchus mykiss, Walbaum), feed and rearing environment, and their antimicrobial activity against 9 fish pathogens. The 64 enterococcal isolates were identified to the species level by polymerase chain reaction (PCR), using specific primers for the different enterococcal species, and confirmed by superoxide dismutase gene sequencing. Enterococcus faecium and E. hirae were the most common species (42.2 and 35.9%, respectively). A total of 48 isolates (75%) showed phenotypic resistance to at least 1 antibiotic determined by a disk-diffusion method, and 25 isolates (39.1%) harbored at least 1 antibiotic resistance gene [erm(B), tet(M), tet(S), tet(K), tet(L), tet(T), vanC2, and aad(E)], detected by PCR. One (1.6%) isolate produced gelatinase and none produced hemolysin, using a plate assay. The virulence genes gelE (46.9%), efaAfs (17.2%), agg (1.6%), and hyl (1.6%) were detected by PCR. A total of 48 isolates (75%) exerted antimicrobial activity against 1 or more of the tested fish pathogens, using a stab-on-agar test. From these isolates, 21 (43.8%) harbored at least 1 bacteriocin-encoding gene (entP, entL50A and entL50B, hirJM79, entSE-K4, entQ and entA), detected by PCR. None of the enterococci showed bile deconjugation and mucin degradation abilities. A total of 17 enterococcal isolates (26.6%) that did not harbor any antibiotic resistance or virulence factor were considered safe for application as probiotics, including 6 isolates (35.3%) that showed antimicrobial activity against at least 1 fish pathogen and harbored at least 1 bacteriocin-encoding gene. Rainbow trout, feed, and rearing environment constitute an appropriate source for the isolation of enterococci as potential probiotic for aquaculture.

Bacteriocins and their applications for the treatment of bacterial diseases in aquaculture: a review

Aquaculture is one of the fastest growing food producing sectors in the world. The increase in the world population requires faster growth in aquaculture for better food availability and to overcome malnutrition. But this worldwide growth of aquaculture is overwhelmed by catastrophic fish diseases and spoilage during cultivation and preservation problems caused by pathogenic bacteria. Various remedies are available for food preservation and also from the bacterial diseases in the fish production. Due to the emergence of antibiotic resistance and adverse effects, an alternative to antibiotic is the need of the hour. The proteins such as bacteriocins, i.e. ribosomally synthesized antimicrobial peptides (AMPs) and possess antagonistic against closely related and other bacteria. These proteins are produced by most lineages of bacteria which are playing key roles in recognition and possess a cognate immunity system for self-protection as well as host protection from infections. These proteins are potent immunomodulators with broad spectrum inhibition properties which are further used as novel therapeutic agents. In this review, we have tried to summarize the bacteriocins on the basis of their classifications, structural and functional attributes, mode of actions, bacteriocins isolated from fish and gut microbiota and presence of beneficiary bacteria in the fish gut. Further, this study highlighted where further research is a prerequisite to increase our basic understanding and search for novel bacteriocins to elucidate the proteins/peptides having antimicrobial properties for disease control in aquaculture as an alternative to antibiotics.

Use of plant extracts in fish aquaculture as an alternative to chemotherapy: Current status and future perspectives

Aquaculture is the main source to increase fish supply. Fast development of aquaculture and increasing fish demand lead to intensification of fish culture, magnifying stressors for fish and thus heightening the risk of disease. Until now, chemotherapy has been widely used to prevent and treat disease outbreaks, although use of chemical drugs has multiple negative impacts on environment and human health e.g. resistant bacterial strains and residual accumulation in tissue. Hence, disease management in aquaculture should concentrate on environmentally friendly and lasting methods. Recently, increasing attention is being paid to the use of plant products for disease control in aquaculture as an alternative to chemical treatments. Plant products have been reported to stimulate appetite and promote weight gain, to act as immunostimulant and to have antibacterial and anti-parasitic (virus, protozoans, monogeneans) properties in fish and shellfish aquaculture due to active molecules such as alkaloids, terpenoids, saponins and flavonoids. However, as it is a relatively emerging practice there is still little knowledge on the long-term effects of plant extracts on fish physiology as well as a lack of homogenization in the extract preparation and fish administration of the plant extracts. This article aims to review the studies carried out on the use of plant products on fish aquaculture and their biological effects on fish such as growth promoter, immunostimulant, antibacterial and anti-parasitic. It also intends to evaluate the current state of the art, the methods used and the problems encountered in their application to the aquaculture industry.

Probiotics in fish and shellfish culture: immunomodulatory and ecophysiological responses

Aquaculture is emerging as one of the most viable and promising enterprises for keeping pace with the surging need for animal protein, providing nutritional and food security to humans, particularly those residing in regions where livestock is relatively scarce. With every step toward intensification of aquaculture practices, there is an increase in the stress level in the animal as well as the environment. Hence, disease outbreak is being increasingly recognized as one of the most important constraints to aquaculture production in many countries, including India. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. The development of non-antibiotic and environmentally friendly agents is one of the key factors for health management in aquaculture. Consequently, with the emerging need for environmentally friendly aquaculture, the use of alternatives to antibiotic growth promoters in fish nutrition is now widely accepted. In recent years, probiotics have taken center stage and are being used as an unconventional approach that has numerous beneficial effects in fish and shellfish culture: improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. As natural products, probiotics have much potential to increase the efficiency and sustainability of aquaculture production. Therefore, comprehensive research to fully characterize the intestinal microbiota of prominent fish species, mechanisms of action of probiotics and their effects on the intestinal ecosystem, immunity, fish health and performance is reasonable. This review highlights the classifications and applications of probiotics in aquaculture. The review also summarizes the advancement and research highlights of the probiotic status and mode of action, which are of great significance from an ecofriendly, sustainable, intensive aquaculture point of view.

Medicinal plant derivatives as immunostimulants: an alternative to chemotherapeutics and antibiotics in aquaculture

Aquaculture makes a significant contribution in the production of protein-rich food for human consumption. Aquaculture practices encounter many challenges, and one of the most devastating problems is disease outbreaks caused by microbial pathogens. To control disease outbreaks, several chemotherapeutics and antibiotics were used indiscriminately, which in turn leads to residual problems in the surrounding environment affecting higher animals and also humans. Immunostimulants are considered as an alternative for antibiotics, which will boost the immune system of the cultured organism, thus effectively countering the assault of pathogens. The use of plant materials as immunostimulant will be an ecofriendly approach for the control of pathogens. The botanicals present in the plants have a key role in enhancing the fish immunity. This review focuses on the importance of plant material as immunostimulant in the control of diseases in aquaculture.

Design and evaluation of a unique RT-qPCR assay for diagnostic quality control assessment that is applicable to pathogen detection in three species of salmonid fish

BackgroundThe detection of pathogens at early stages of infection is a key point for disease control in aquaculture. Therefore, accurate diagnostic procedures are a must. Real-time PCR has been a mainstay in diagnostics over the years due to its speed, specificity, sensitivity, reproducibility and throughput; as such, real-time PCR is a target for improvement. Nevertheless, to validate a novel diagnostic tool, correct setup of the assay, including proper endogenous controls to evaluate the quantity and quality of the samples and to detect possible sample degradation, is compulsory. This work aims to design a unique RT-qPCR assay for pathogen detection in the three salmonid species reared in Chile. The assay uses elongation factor 1 alpha as the single endogenous control, thus avoiding the need for multiple endogenous controls, as well as multiple validations and non-comparable quality control parameters.ResultsThe in vivo and in vitro analyses of samples from Salmo salar, Oncorhynchus mykiss and Oncorhynchus kisutch showed that when primers were accurately selected to target conserved regions of the elongation factor 1 alpha (ELF1α) gene, a single novel RT-qPCR assay yielding similar and reproducible Ct values between the three species could be designed. The opposite occurred when an assay originally designed for Salmo salar was tested in samples from the two species of the genus Oncorhynchus.ConclusionsHere, we report the design and evaluation of an accurate trans-species RT-qPCR assay that uses the elongation factor 1 alpha (ELF1α) gene as an endogenous control and is applicable for diagnostic purposes in samples obtained from the three salmonid species reared in Chile.

Review: Developments in the use of probiotics for disease control in aquaculture

Abstract Probiotics, which are regarded as micro-organisms administered orally leading to health benefits, are used extensively in aquaculture for disease control, notably against bacterial diseases. In contrast to use with terrestrial animals where lactic-acid producing bacteria dominate, a diverse range of micro-organisms including Gram-negative and Gram-positive bacteria have been considered in aquaculture. The source of these organisms is often the digestive tract of the host animal. The mode of action includes competitive exclusion and immunomodulation. Probiotics may also improve appetite and lead to enhanced growth and better feed conversion.

Effects of traditional Chinese medicines (TCM) on the immune response of grass carp (Ctenopharyngodon idellus)

The use of traditional Chinese medicine (TCM) in aquaculture has been widely investigated. It is believed that herbal supplements could enhance the immunity and promote fish growth. The powdered TCM or its decoction can be easily applied in the form of feed supplements by direct incorporation into fish feeds and side effects are seldom found. In this study, Radix scutellaria (Rs) and Rhizoma coptidis (Rc) showed strong bacterial inhibition on Aeromonas hydrophila out of the sixteen selected herbal extracts. Four TCMs, R. scutellaria, R. coptidis, Herba andrographis (Ha), and Radix sophorae flavescentis (Rsf) were selected to form a compound formulation in the ratio of 1:1:2:3. A feeding experiment on grass carp was conducted with addition of the above TCM formulation (0.5, 1 and 2 % w/w) in the fish feed, and bactericidal activity, total protein and immunoglobulin in blood plasma, and nitroblue tetrazolium activity in the whole blood were measured. 2 % supplementation significantly improved (p < 0.05) the bactericidal activity and total immunoglobulin in the plasma after feeding for 21 days. Compared to control, 2 % TCM feeding groups showed a significantly lower mortality after A. hydrophila challenge at the end of experiment and the same result was archived in field trial. In the cost evaluation, the use of the TCM formulation in grass carp culture was insignificant and could be compensated by improved yield. TCM formulation contained different active ingredients including some immuno-stimulant and antimicrobial agents and therefore could be applicable to multiple diseases. Application of this TCM formulation would be a cost-effective and prophylactic approach for disease control in aquaculture, replacing the use of antibiotics for treating enteritis and even other general diseases.

The development of novel prophylaxis from microbes and plant sources for disease control in aquaculture

The development of novel prophylaxis from microbes and plant sources for disease control in aquaculture

Detection of bacterial pathogens in aquaculture samples by DNA microarray analysis

Rapid, sensitive, and specific detection of pathogens is important for effective disease control in aquaculture. However, the use of conventional microbiological methods for pathogen detection is often limited by the time required to complete the assays. The aim of this study was to develop a DNA microarray assay to detect 8 species of pathogenic bacteria, i.e., Vibrio harveyi, V. alginolyticus, V. parahaemolyticus, V. anguillarum, V. cholerae, Nocardia seriolae, Aeromonas hydrophila, and Streptococcus iniae, in cultured aquatic animals. Probes were designed according to a variable region of the bacterial 16S rRNA gene and gryB sequences, and 23 probes were finally selected by hybridization with 25 bacterial type cultures. The microarray sensitivity for V. anguillarum detection in healthy fish blood was ≥100CFU/mL. Pathogenic bacteria in blood samples from 21 diseased aquacultural samples were analyzed in a blinded fashion by using the microarray, conventional culture, and 16S rRNA gene sequencing methods; the results of the microarray assay agreed well with those of the conventional culture and 16S rRNA gene sequencing methods. The results of this study show that the microarray method described is suitable for preliminary diagnoses or for confirmation of the main potential pathogens in aquatic animals.

Simultaneous identification of five marine fish pathogens belonging to the genera Tenacibaculum, Vibrio, Photobacterium and Pseudomonas by reverse line blot hybridization

The aim of this work was to develop a reverse line blot hybridization (RLB) assay for the identification of five fish pathogens ( Tenacibaculum soleae, Tenacibaculum maritimum, Vibrio harveyi, Photobacterium damselae and Pseudomonas baetica) of importance in marine aquaculture. Species-specific probes were designed targeting the 16S–23S intergenic spacer region (ISR) or the 23S rRNA gene. Reference and clinical strains of each target species were all correctly identified by the RLB assay, whereas all non-target strains gave unambiguous negative results with the exception of cross-reactivity between the V. harveyi probe and V. campbellii PCR product. Sensitivity limits of the RLB assay using pure cultures varied among the five target organisms from 1 to 100 pg of genomic DNA. To our knowledge, this is the first RLB protocol developed for identification of bacterial fish pathogens, and also constitutes the first molecular diagnosis tool available for P. baetica. It will be helpful for epidemiological studies and for the control of diseases in aquaculture.

Stress response for disease control in aquaculture

AbstractHeat shock proteins (Hsps) are robustly induced by diverse stressors that denature proteins. In addition to stress resistance, Hsps are involved in the folding of nascent proteins, plant and animal development, aging, environmental adaptation and the immune response, demonstrating the fundamental importance of these proteins to cell survival. Heat shock proteins are induced in aquatic organisms by perturbations of temperature and salinity, environmental contaminants, handling, hormones and biotic stressors. Exposure to sublethal stress may enhance tolerance to a subsequent stress, a process termed induced thermotolerance, and provide protection to stressors other than the initial stress, known as cross‐tolerance. In the present review, we briefly describe the established approaches that are used to control disease during aquaculture. This is followed by documentation of Hsp induction after exposure to stressors commonly encountered by aquatic organisms. Induced thermotolerance, cross‐tolerance and immune enhancement by Hsps are also considered. Although physiological stress is known to decrease disease resistance it is now becoming clear that stress‐induced Hsps enhance the tolerance of aquatic organisms to disease. Potential applications for Hsps in the commercial production of fish, crustaceans and molluscs are indicated, an issue of significance when the importance of aquaculture in feeding the world’s population is realized.

The contribution of molecular epidemiology to the understanding and control of viral diseases of salmonid aquaculture

Molecular epidemiology is a science which utilizes molecular biology to define the distribution of disease in a population (descriptive epidemiology) and relies heavily on integration of traditional (or analytical) epidemiological approaches to identify the etiological determinants of this distribution. The study of viral pathogens of aquaculture has provided many exciting opportunities to apply such tools. This review considers the extent to which molecular epidemiological studies have contributed to better understanding and control of disease in aquaculture, drawing on examples of viral diseases of salmonid fish of commercial significance including viral haemorrhagic septicaemia virus (VHSV), salmonid alphavirus (SAV) and infectious salmon anaemia virus (ISAV). Significant outcomes of molecular epidemiological studies include:Improved taxonomic classification of virusesA better understanding of the natural distribution of virusesAn improved understanding of the origins of viral pathogens in aquacultureAn improved understanding of the risks of translocation of pathogens outwith their natural host rangeAn increased ability to trace the source of new disease outbreaksDevelopment of a basis for ensuring development of appropriate diagnostic toolsAn ability to classify isolates and thus target future research aimed at better understanding biological functionWhile molecular epidemiological studies have no doubt already made a significant contribution in these areas, the advent of new technologies such as pyrosequencing heralds a quantum leap in the ability to generate descriptive molecular sequence data. The ability of molecular epidemiology to fulfil its potential to translate complex disease pathways into relevant fish health policy is thus unlikely to be limited by the generation of descriptive molecular markers. More likely, full realisation of the potential to better explain viral transmission pathways will be dependent on the ability to assimilate and analyse knowledge from a range of more traditional information sources. The development of methods to systematically record and share such epidemiologically important information thus represents a major challenge for fish health professionals in making the best future use of molecular data in supporting fish health policy and disease control.

Molecular cloning and transcriptional analysis of a newly identified anti-lipopolysaccharide factor gene in kuruma shrimp, Marsupenaeus japonicus

In the present study, we have cloned a new family of anti-lipopolysaccharide factor (ALF) from haemocytes of kuruma shrimp Marsupenaeus japonicus (MjALF2) using RACE method. Transcriptional analysis of MjALF2 gene in the organs of healthy shrimp revealed prominent expression in gills and muscle. In vitro LPS stimulation in the lymphoid organ cells resulted in significant increase in expression at 48, 8 and 12 h poststimulation, compared to the nonstimulated cells. In vivo injection of V. penaeicida does not show any high expression in time course assay. Phylogenetic analysis showed MjALF2 is placed in the group closer to P. monodon isoform 1 and 2 than to MjALF1. The full-length MjALF2 gene consists of 558 bp with a 363 -bp open reading frame, encoding 121 amino acids. The deduced peptide contains a putative signal peptide of 22 amino acids with molecular mass of about 13.8 kDa molecular mass. The deduced amino acid sequence of MjALF2 showed 83.3 and 56.7% identity with ALF sequences of P. monodon. The present work revealed the presence of MjALF2 gene, which is highly expressed in gills and muscle of healthy kuruma shrimp. Further studies are required to clarify the involvement of MjALF2 in immune responses for using as a therapeutic agent. Antimicrobial peptides are promising potential therapeutic agents for disease control in aquaculture. Understanding the relation of MjALF2 with innate immunity mechanism will lead to develop better health management strategies for long-term sustainability of the shrimp industry.

A relationship between antimicrobial peptide gene expression and capacity of a selected shrimp line to survive a Vibrio infection

Understanding of antimicrobial defence mechanisms of penaeid shrimp should help in the design of efficient strategies for the management and disease control in aquaculture. In this study, we have specifically analysed the expression in circulating hemocytes of antimicrobial peptides (AMPs) encoding genes, such as PEN2 and PEN3, ALF, crustin, lysozyme and a putative cysteine-rich peptide. We evidenced a relationship between the level of expression of some AMPs and the successful response of the shrimp, Litopenaeus stylirostris, to circumvent a pathogenic Vibrio penaeicida infection. Additionally, significant differences in some AMP transcript amounts are evidenced between control, non-selected shrimp line and the third generation breeding of shrimp selected for their survival to natural V. penaeicida infections. On the basis of these results, it will now be of great interest to determine if these AMPs are directly involved in the resistance of shrimp to infection or if they only reflect other acquired defence mechanisms which can confer a resistance.

Molecular cloning, genomic organization and functional analysis of an anti-lipopolysaccharide factor from Chinese mitten crab Eriocheir sinensis

Anti-lipopolysaccharide factor (ALF) represents one kind of basic proteins, which binds and neutralizes LPS and exhibits strong antibacterial activity against Gram-negative R-type bacteria. The ALF gene of Chinese mitten crab Eriocheir sinensis (Milne Edwards, 1853) (denoted as EsALF) was identified from haemocytes by expressed sequence tag (EST) and PCR approaches. The full-length cDNA of EsALF consisted of 700 nucleotides with a canonical polyadenylation signal-sequence AATAAA, a polyA tail, and an open-reading frame of 363bp encoding 120 amino acids. The high similarity of EsALF-deduced amino acid sequence shared with the ALFs from other species indicated that EsALF should be a member of ALF family. The mRNA expression of EsALF in the tissues of heart, gonad, gill, haemocytes, eyestalk and muscle was examined by Northern blot analysis and mRNA transcripts of EsALF were mainly detected in haemocytes, heart and gonad. The temporal expression of EsALF in haemocytes after Vibrio anguillarum challenge was recorded by quantitative real-time RT-PCR. The relative expression level of EsALF was up-regulated rapidly at 2 h post-injection and reached 3-fold to that in blank group. After a drastic decrease to the original level from 4 to 8 h, the expression level increased again and reached 4-fold to that in the blank group at 12 h post-injection. The genomic DNA sequence of EsALF gene consists of 1174 bp containing three exons and two introns. The coding sequence of the EsALF mature peptide was cloned and expressed in Escherichia coli BL21(DE3)-pLysS to further elucidate its biological functions. The purified recombinant product showed bactericidal activity against both Gram-positive (G+) and Gram-negative (G-) bacteria, which demonstrated that the rEsALF was a broad-spectrum antibacterial peptide. All these results indicated that EsALF was an acute-phase protein involved in the immune responses of Chinese mitten crab, and provided a potential therapeutic agent for disease control in aquaculture.

Molecular cloning, expression of a big defensin gene from bay scallop Argopecten irradians and the antimicrobial activity of its recombinant protein

Antimicrobial peptides are important components of the host innate immune responses by exerting broad-spectrum microbicidal activity against pathogenic microbes. The first mollusk big defensin (designated AiBD) cDNA was cloned from bay scallop Argopecten irradians by expressed sequence tag (EST) and rapid amplification of cDNA ends (RACE) techniques. The scallop AiBD consisted of 531 nucleotides with a canonical polyadenylation signal sequence AATAAA and a poly(A) tail, encoding a polypeptide of 122 amino acids. The high similarity of AiBD deduced amino acid sequence with big defensin from Tachypleus tridentatus and Branchiostoma belcheri tsingtaunese indicated that AiBD should be a member of big defensin family. The expression of AiBD in various tissues was measured by using Northern blotting analysis. mRNA transcripts of AiBD could be detected in haemocytes of unchallenged scallops. The temporal expression of AiBD in haemolymph after Vibrio anguilarum challenge was recorded by quantitative real time PCR. The relative expression level of AiBD in haemolymph was up-regulated evenly in the first 8 h, followed by a drastic increase, and increased 131.1-fold at 32 h post-injection. These results indicated that AiBD could be induced by bacterial challenge, and it should participate in the immune responses of A. irradians. Biological activity assay revealed that recombinant AiBD could inhibit the growth of both Gram-positive and Gram-negative bacteria, and also showed strong fungicidal activity towards the expression host. Recombinant expression of AiBD made it possible to further characterize its functions involved in immune responses, and also provided a potential therapeutic agent for disease control in aquaculture.