Disease Control In Aquaculture Research Articles

Evaluation of a Low-Temperature Immersion Immunization Strategy for the Infectious Spleen and Kidney Necrosis Virus orf037l Gene-Deleted Attenuated Vaccine

Background: Infectious spleen and kidney necrosis virus (ISKNV) poses a significant threat to aquaculture sustainability, particularly affecting mandarin fish (Siniperca chuatsi) and causing significant economic losses. Methods: To address this challenge, this study developed an ISKNV Δorf037l vaccine strain, where the orf037l gene was knocked out. Infection assays conducted at 28 °C showed that the knocking out the orf037l gene decreased the virulence of ISKNV and reduced lethality against mandarin fish by 26.7% compared to wild-type ISKNV. To further diminish residual virulence, the effect of low-temperature (22 °C) immersion immunization was evaluated. Results: The results indicate that low temperature significantly diminished the virulence of the Δorf037l vaccine strain, elevating the survival rate of mandarin fish to 90%. Furthermore, the vaccine strain effectively triggered the expression of crucial immune-related genes, such as IFN-h, IL-1, IκB, Mx, TNF-α, and Viperin, while inducing the production of specific neutralizing antibodies. Low-temperature immersion with Δorf037l achieved a high relative percentage of survival of 92.6% (n = 30) in mandarin fish, suggesting the potential of Δorf037l as a promising immersion vaccine candidate. Conclusions: These findings contribute to advancing fish immersion vaccine development and demonstrate the importance and broad applicability of temperature optimization strategies in vaccine development. Our work carries profound implications for both the theoretical understanding and practical application in aquaculture disease control.

Designing of a Novel Aerolysin-based Multiepitope Vaccine against Aeromonas hydrophila Isolated from Osphronemus goramy Using Reverse Vaccinology: an in Silico Approaches

Graphical Abstract Highlight Research The study aims to develop a multi-epitope vaccine (MEV) against A. hydrophila by targeting the aerolysin toxin, a key virulence factor responsible for infections in fish and humans. Computational methods identified and optimized B-cell and T-cell epitopes, focusing on their ability to trigger immune responses without causing toxicity or allergenicity. In silico simulations demonstrated that the MEV has a strong binding affinity to immune receptors like TLR-4, MHC-I, and MHC-II, indicating its potential to induce robust cellular and humoral immunity. Structural analysis of the MEV showed a stable 3D conformation, with most residues in favorable regions, ensuring stability during immune activation. The MEV could enhance disease control in aquaculture and reduce human infection risks, offering a promising solution to address antibiotic resistance and the absence of effective vaccines. Abstract Aeromonas hydrophila, gram-negative, is a major pathogen responsible for various diseases in mammals, reptiles, amphibia, and vertebrates, including fish and humans. Targeting the specific toxin aerolysin in A. hydrophila is crucial to address antibiotic resistance and the lack of adequate and protective vaccines against this intracellular pathogen. This study aimed to identify a multi-epitope vaccination (MEV) candidate targeting A. hydrophila aerolysin toxin to combat the disease effectively. Standard biochemical characterization methods and sequencing of the 16S rRNA, rpoB, and aerA genes identified the isolate AHSA1 as A. hydrophila. Subsequently, we identified B and T cell epitopes on the aerolysin protein and separately predicted MHC-I and MHC-II epitopes. The epitopes are then evaluated for toxicity, antigenicity, allergenicity, and solubility. The vaccine design integrated multi-epitope-based constructs, utilizing specialized linkers (GPGPG) and EAAAK linkers to connect epitope peptides with adjuvants in the cholera toxin B component, thereby enhancing immunogenicity. Ramachandran plots showed that 85.25% of the residues were located in the most favorable regions, which was followed by the generously allowed zone (1.30%), the additional allowed regions (10.80%), and the forbidden regions (2.65%), thus confirming the feasibility of the modeled vaccine design. Based on docking simulations, MEV had the highest binding and interaction energies with TLR-4, TLR-9, MHC-I, and MHC-II (-1081.4, -723.2, 866.2, -9043.3 kcal/mol). Based on computational modelling, we expect the Aerolysin MEV candidate design to activate diverse immune mechanisms, stimulate robust responses against A. hydrophila, and maintain safety. The significant solubility, absence of toxicity or allergic response, and minimal side effects in animal testing all contribute to the potential clinical utility of this vaccine candidate.

Response signatures of intestinal microbiota and gene transcription of yellow catfish (Pelteobagrus fulvidraco) to Aeromonas hydrophila infection

Bacterial intestinal inflammation is a common disease of yellow catfish (Pelteobagrus fulvidraco) in high-density aquaculture. Understanding the interactions between host and intestinal bacteria is helpful to intestinal inflammatory disease control. Here, we constructed a model of intestinal inflammation after Aeromonas hydrophila infection in yellow catfish, and characterized variations in gene expression and microbiome in the gut through high-throughput sequencing. Furthermore, host gene-microbiome interactions were identified. Histology observation showed disordered distribution of columnar epithelial cells and decrease of goblet cells in intestine. A total of 4741 genes showed differentially expression, mostly in comparisons between 12 hpi group with each other groups respectively, including control, 24 hpi and 48 hpi groups. These genes were enriched in immune-related pathways including the IL-17 signaling pathway, triggering strong inflammatory response at the invading stage within 12 h. Subsequently, the host strengthened energy consumption by activating carbohydrate and lipid metabolism pathways to repair the intestinal mucosal immune defense line. In addition, fish with A. hydrophila infection show decreased richness of gut microbial, reduced relative abundance of probiotics including Akkermansia, and elevated pathogenic bacteria such as Plesimonas. An integrative analysis identified A. hydrophila-related genes, such as il22 and stat3, for which expression level is close associated with the shift of A. hydrophila-related bacteria relative abundance, such as Akkermansia and Cetobacterium. Aside from picturing the variations of intestine gene expression and mucosal microbiome of yellow catfish coping with A. hydrophila infection, our study probed the underlying host-microbe interactions in A. hydrophila infection induced intestinal inflammatory, providing new insights for disease control in aquaculture.

Immunomodulatory Effects of Mallotus japonicus Extract on Innate Immune Responses in HeteroTilapia buttikoferi Infected with Aeromonas hydrophila

The intensive use of antibiotics in modern aquaculture has been linked to the emergence of multidrug resistance in human health. Despite continuous caution against such use by farmers, antibiotics serve as the primary means of disease control in aquaculture. In this study, we explore the potential of medicinal plant extracts as immunomodulant in enhancing the innate immune defense of a fish host, HeteroTilapia buttikoferi, infected with the prevalent fish pathogenic bacteria Aeromonas hydrophila. Our previous research reveals the bactericidal activity of the medicinal plant, Mallotus japonicus, against the pathogen, but its effectiveness as a prophylactic in enhancing host immune defense has not yet been investigated. Therefore, the objective of this study is to address this knowledge gap.By our findings, it was uncovered that the supplementation of the diethyl ether extract of the plant’s bark as an additive in the fish diet significantly improved the innate immune defense by upregulating the total levels of lysozyme, serum bactericidal activity, globulin and albumin levels, total protein, phagocytosis, respiratory burst activity and overall survival. A dose-dependent increase in immunological parameters was recorded, and this was in sharp contrast to the control group.These findings suggest that M. japonicus has the potential of use to enhance the innate immune defense of H. buttikoferi against the pervasive fish pathogenic bacteria, Aeromonas hydrophila. The improvements in immune parameters indicate the ability of M. japonicus extract to strengthen the hosts to combat bacterial infections.

Phytotherapy use for disease control in aquaculture: a review of the last 5 years

Phytotherapy use for disease control in aquaculture: a review of the last 5 years

High‐throughput genotyping in estimating genetic resources and detecting pathogens in aquaculture

High‐throughput genotyping in estimating genetic resources and detecting pathogens in aquaculture

Transcriptomic analysis of regenerated skins reveals key genes involved in skin immune response and air-breathing of loach (Paramisgurnus dabryanus)

Fish skin acts as the first immune barrier against pathogens from external environments. Recently, fish skin immunity research has gradually become a hot topic in aquaculture disease control. Interestingly, the skin can do air-breathing in some bimodal respiration fish. However, there is no comprehensive understanding of these two functions. In this study, the skin regeneration of loach (Paramisgurnus dabryanus) was investigated through morphological and histological observations. Then, original skins (OS) and the regenerated skins (RS) when their capillaries were the most abundant during healing, were collected for transcriptomic analysis. 285,899,386 clean reads with a total length of 42.34 Gb were obtained. A total of 1282 differentially expressed genes (DEGs) were detected, including 1030 DEGs up-regulated and 252 DEGs down-regulated in the comparison of RS vs. OS. Fc gamma R-mediated phagocytosis (containing gelsolin (Gsn)), chemokine signaling pathway (containing C–C motif chemokine ligand 28 (Ccl28)), and B cell receptor signaling pathway (containing CD80 molecule (Cd81)) were closely related to skin immune response of the loach. PI3K-Akt signaling pathway [containing fibronectin 1 (Fn1) and lysyl oxidase-like 2b (Loxl2b)], TGF-beta signaling pathway [containing thrombospondin 1 (Thbs1)], ECM-receptor interaction [containing integrin alpha 7 (Itga7), Itgb8, Itgb10 and Itgb5], and dilated cardiomyopathy [containing laminin subunit alpha1 (Lama1)] were closely associated with skin air-breathing of the loach. This study is conducive to explore the molecular mechanisms of skin immune response during its regeneration and air-breathing of bimodal respiration fish. This study will benefit for the aquaculture of P. dabryanus and its related species.

Intestinal microbiota signatures of common carp (Cyprinus carpio) after the infection of Aeromonas hydrophila

Common carp is an important freshwater farmed fish species worldwide. Intensive rearing in aquaculture causes increasing susceptibility to various pathogens. One of the most frequently encountered pathogens is Aeromonas hydrophila, which has caused huge economic losses to the common carp industry. Extensive studies have been reported on the genetic mechanism underlying common carp against A. hydrophila at the molecular level, however, the influence of intestinal microbiota on host resistance to pathogen is less studied. In the present study, we analyzed the composition and biodiversity of intestinal microbiota in common carp following A. hydrophila infection by utilizing 16S rDNA sequencing. Collectively, the intestinal microbiota in common carp is diverse, but dominated by four phyla, Proteobacteria, Bacteroidetes, Fusobacteria and Firmicutes. The diversity and richness of microbiota was obviously decreased after infection of A. hydrophila. The composition and relative abundance of gut microbiota was significantly altered upon pathogenic invasion. The relative abundance of genera Cetobacterium and Vibrio were significantly increased in the infected groups. Further investigating the divergence of microbes between the resistant fish and susceptible fish showed that the relative abundance of Lactococcus, Akkermansia and Vibrio in resistant fish were significantly higher than that in both the susceptible fish and the control fish, indicating their potential correlation with the host resistance against pathogens. Our study could not only elucidate the dynamic changes in the common carp intestinal microbiota that occur in response to A. hydrophila, but also help us understand the underlying mechanism of intestinal microbial community in resisting pathogens and might suggest strategies for disease control in aquaculture.

Cecropin P1 antimicrobial peptide modulates differential expression of immune relevant genes in rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1

Accumulated evidence indicates that antimicrobial peptides modulate immune activities in fish. In this study, we profiled the differential expression patterns of representative immune relevant genes in an epithelial-like cell line of rainbow trout gill, RTgill-W1, in response to exposure of cecropin P1 antimicrobial peptide. RTgill-W1 cells were treated with synthetic cecropin P1 over time (0, 2, 4 and 24 h) with or without the present of lipopolysaccharide (LPS) or polyinosinic polycytidylic acid (PolyI:C). The relative abundances of each mRNA were measured by real-time quantitative PCR. The dose-response study revealed significant perturbations of mRNA levels of genes related to pro-inflammation, acute phase, surface proteins and transcription factors at 30 μM of cecropin P1. In addition, cecropin P1 altered the differential expression patterns that were induced by LPS or PolyI:C, at different time points in RTgill-W1. Overall, our results indicate that cecropin P1 exhibits pro-inflammation activity, modulate cell-cell interaction and cytokine signal transduction in rainbow trout gill cell, and may suggest a potential application of this peptide as an immune adjuvant for disease control in aquaculture.

A Multiplexed, Tiled PCR Method for Rapid Whole-Genome Sequencing of Infectious Spleen and Kidney Necrosis Virus (ISKNV) in Tilapia.

Tilapia farming is one of the most important sectors in aquaculture worldwide and of major importance to global food security. Infectious spleen and kidney necrosis virus (ISKNV) has been identified as an agent of high morbidity and mortality, threatening tilapia aquaculture. ISKNV was detected in Lake Volta, Ghana, in September 2018 and spread rapidly, with mortality rates between 60 and 90% and losses of more than 10 tonnes of fish per day. Understanding the spread and evolution of viral pathogens is important for control strategies. Here, we developed a tiled-PCR sequencing approach for the whole-genome sequencing of ISKNV, using long read sequencing to enable field-based, real-time genomic surveillance. This work represents the first use of tiled-PCR for whole genome recovery of viruses in aquaculture, with the longest genome target (>110 kb dsDNA) to date. Our protocol was applied to field samples collected from the ISKNV outbreaks from four intensive tilapia cage culture systems across Lake Volta, between October 2018 and May 2022. Despite the low mutation rate of dsDNA viruses, 20 single nucleotide polymorphisms accumulated during the sampling period. Droplet digital PCR identified a minimum requirement of template in a sample to recover 50% of an ISKNV genome at 275 femtograms (2410 viral templates per 5 µL sequencing reaction). Overall, tiled-PCR sequencing of ISKNV provides an informative tool to assist in disease control in aquaculture.

Genotypic Characterization of Infectious Spleen and Kidney Necrosis Virus (ISKNV) in Southeast Asian Aquaculture

Infectious spleen and kidney necrosis virus (ISKNV) is a species within the genus Megalocytivirus (family Iridoviridae), which causes high mortality disease in many freshwater and marine fish species. ISKNV was first reported in Asia and is an emerging threat to aquaculture with increasing global distribution, in part due to its presence in ornamental fish with clinical and subclinical infections. The species ISKNV includes three genotypes: red seabream iridovirus (RSIV), turbot reddish body iridovirus (TRBIV), and ISKNV. There is an increasing overlap in the recognized range of susceptible fish hosts and the geographic distribution of these distinct genotypes. To better understand the disease caused by ISKNV, a nucleic acid hybridization capture enrichment was used prior to sequencing to characterize whole genomes from archived clinical specimens of aquaculture and ornamental fish from Southeast Asia (n = 16). The method was suitable for tissue samples containing 2.50 × 104–4.58 × 109 ISKNV genome copies mg−1. Genome sequences determined using the hybridization capture method were identical to those obtained directly from tissues when there was sufficient viral DNA to sequence without enrichment (n = 2). ISKNV genomes from diverse locations, environments, and hosts had very high similarity and matched established genotype classifications (14 ISKNV genotype Clade 1 genomes with >98.81% nucleotide similarity). Conversely, two different genotypes were obtained at the same time and location (RSIV and ISKNV from grouper, Indonesia with 92.44% nucleotide similarity). Gene-by-gene analysis with representative ISKNV genomes identified 59 core genes within the species (>95% amino acid identity). The 14 Clade 1 ISKNV genomes in this study had 100% aa identity for 92–105 of 122 predicted genes. Despite high overall sequence similarity, phylogenetic analyses using single nucleotide polymorphisms differentiated isolates from different host species, country of origin, and time of collection. Whole genome studies of ISKNV and other megalocytiviruses enable genomic epidemiology and will provide information to enhance disease control in aquaculture.

The antibacterial activity and antibacterial mechanism analyses of an LRR-IG protein in the Chinese mitten crab, Eriocheir sinensis

Leucine-rich repeat and immunoglobulin domain containing protein (LRR-IG) family is an important class of immune molecules in invertebrates. Herein, a novel LRR-IG, named as EsLRR-IG5, was identified from Eriocheir sinensis. It contained typical structures of LRR-IG including an N-terminal LRR region and three IG domains. EsLRR-IG5 was ubiquitously expressed in all the tested tissues, and its transcriptional levels increased after being challenged with Staphylococcus aureus and Vibrio parahaemolyticus. Recombinant proteins of LRR and IG domains from the EsLRR-IG5 (named as rEsLRR5 and rEsIG5) were successfully obtained. rEsLRR5 and rEsIG5 could bind to both gram-positive bacteria and gram-negative bacteria as well as lipopolysaccharide (LPS) and peptidoglycan (PGN). Moreover, rEsLRR5 and rEsIG5 exhibited antibacterial activities against V. parahaemolyticus and V. alginolyticus and displayed bacterial agglutination activities against S. aureus, Corynebacterium glutamicum, Micrococcus lysodeikticus, V. parahaemolyticus and V. alginolyticus. The scanning electron microscopy (SEM) observation revealed that the membrane integrity of V. parahaemolyticus and V. alginolyticus was destroyed by rEsLRR5 and rEsIG5, which may lead to the leakage of cell contents and death. This study provided clues for further studies on the immune defense mechanism mediated by LRR-IG in crustaceans and provided candidate antibacterial agents for prevention and control of diseases in aquaculture.

Comparative study of the effects of Montanide™ ISA 763A VG and ISA 763B VG adjuvants on the immune response against Streptococcus agalactiae in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae is regarded as a major bacterial pathogen of farmed fish, with outbreaks in Nile tilapia causing significant losses. Vaccination is considered the most suitable method for disease control in aquaculture, with the potential to prevent such outbreaks if highly efficacious vaccines are available for use. Several vaccines have been produced to protect against S. agalactiae infection in tilapia, including inactivated vaccines, live attenuated vaccines, and subunit vaccines, with variable levels of protection seen. Two commercial adjuvants, Montanide™ ISA 763A VG and ISA 763B VG, have been developed recently and designed to improve the safety and efficacy of oil-based emulsions delivered by intraperitoneal injection. In particular, their mode of action may help identify and stimulate particular immunological pathways linked to the intended protective response, which is an important tool for future vaccine development. Therefore, this study aimed to characterize the potential of two adjuvanted-bacterial vaccines against S. agalactiae (SAIV) comparatively, to determine their usefulness for improving protection and to analyse the immune mechanisms involved. Nile tilapia were divided into four groups: 1) fish injected with PBS as a control, 2) fish injected with the SAIV alone, 3) fish injected with the SAIV + Montanide™ ISA 763A VG, and 4) fish injected with the SAIV + Montanide™ ISA 763B VG. Following immunization selected innate immune parameters were analysed, including serum lysozyme, myeloperoxidase, and bactericidal activity, with significantly increased levels seen after immunization. Cytokines associated with innate and adaptive immunity were also studied, with expression levels of several genes showing significant up-regulation, indicating good induction of cell-mediated immune responses. Additionally, the specific IgM antibody response against S. agalactiae was determined and found to be significantly induced post-vaccination, with higher levels seen in the presence of the adjuvants. In comparison to the protection seen with the unadjuvanted vaccine (61.29% RPS), both Montanide™ ISA 763A VG and Montanide™ ISA 763B VG improved the RPS, to 77.42% and 74.19% respectively. In conclusion, Montanide™ ISA 763A VG and Montanide™ ISA 763B VG have shown potential for use as adjuvants for fish vaccines against streptococcosis, as evidenced by the enhanced immunoprotection seen when given in combination with the SAIV vaccine employed in this study.

Single-cell metabolome profiling for phenotyping parasitic diseases in phytoplankton

Bloom-forming phytoplankton are key players in aquatic ecosystems, fixing carbon dioxide and forming the base of the marine food web. Diverse stresses, such as nutrient depletion, temperature increase, and pathogen emergence can influence the health and dynamics of algal populations. While population responses to these stressors are well-documented in the aquatic ecosystems, little is known about the individual cellular adaptations. These are however the key to an in-depth physiological understanding of microbiome dynamics in the plankton. Finding solutions to disease control in aquaculture also depends on knowledge of infection dynamics and physiology in algae. Single-cell metabolomics can give insight into infection processes by providing a snapshot of small molecules within a biological system. We used a single-cell metabolome profiling workflow to track metabolic changes of diatoms and dinoflagellates subjected to parasite infection caused by the oomycete Lagenisma coscinodisci and the alveolate Parvilucifera spp. We accurately classified the healthy phenotype of bloom-forming phytoplankton, including the diatoms Coscinodiscus granii and Coscinodiscus radiatus, and the toxic dinoflagellate Alexandrium minutum. We discriminated the infection of the toxic dinoflagellate A. minutum with the alveolate parasitoids Parvilucifera infectans and P. rostrata down to the single-cell resolution. Strain and species-specific responses of the diatom hosts Coscinodiscus spp. Infected with the oomycete pathogen Lagenisma coscinodisci could be recognized. LC-HRMS and fragmentation pattern analysis enabled the structure elucidation of metabolic predictors of infection (guanine, xanthine, DMSP, and pheophorbide). The purine salvage pathway and DMSP lysis could be assigned as regulated processes during host invasion. The findings establish single-cell metabolome profiling with LDI-HRMS coupled with classification analysis as a reliable diagnostic tool to track metabolic changes in algae.

Cryptochrome 1 is involved in anti-bacterial immunity in Japanese flounder (Paralichthys olivaceus)

Cryptochrome is a pivotal protein of the core regulatory machinery in circadian clock and participates in various biological processes including immunity. In fish, the immunological functionality of Cryptochrome is unclear. In this study, we profiled the expression pattern of Japanese flounder cryptochrome 1 (named PoCry1) and investigated its involvement in the immune response during bacterial infection. PoCry1 is approximately 75% identical in amino acid sequence to mammalian Cryptochrome 1 and possesses the conserved DNA photolyase domain and FAD binding domain. Its transcription was detected in 10 flounder tissues and was reduced upon Vibrio harveyi challenge. The transcription of PoCry1 exhibited apparent rhythmic oscillation upon the light actuation of a day-night cycle in different tissues. The knockdown of PoCry1 resulted in significant augment of inflammatory cytokine expression. During bacterial infection, PoCry1 silencing led to increase in cytokine expression and decrease in bacterial dissemination, which could be neutralized by a specific PKA inhibitor, suggesting PoCry1 is likely able to negatively modulate the immune response to bacterial infection through PKA associated pathways.Taken together, our results revealed that PoCry1 is circadian oscillated in transcription upon rhythmic light stimulation and involved in anti-infection immunity, thus enlightening that light condition as a circadian zeitgeber could be exploited to strength fish immune system and benefit disease control in aquaculture.

Inhibitory effect of probiotic Bacillus spp. isolated from the digestive tract of Rhynchocypris Lagowskii on the adhesion of common pathogenic bacteria in the intestinal model

Diseases of fish caused by pathogenic bacteria are an important constraint on aquaculture production. Antibiotics have been widely used to control infectious diseases, but this has led to the emergence of drug-resistant bacteria and affected human health. In this context, probiotics are used as an alternative to antibiotics for the prevention and control of diseases in aquaculture. The aim of this study was to obtain probiotic candidate strains of Bacillus spp. from the gut of Rhynchocypris Lagowskii. Strains were screened by enzyme-producing ability, antagonism assay and antibiotic susceptibility. The safety of the strains to host fish has also been established. The isolated Bacillus licheniformis (LSG1-1) and Bacillus subtilis (LSG2-1) were characterized and performed well in tolerance experiments. In addition, LSG1-1 and LSG2-1 were detected to have higher self-aggregation ability and surface hydrophobicity. In the in vitro adhesion model, LSG1-1 and LSG2-1 showed good adhesion ability and had obvious adhesion inhibitory effect on three pathogens of Aeromonas. Based on the characteristics observed so far, Bacillus licheniformis LSG1-1 and Bacillus subtilis LSG2-1 could form potential probiotic candidates in the digestive tract of R. lagowskii to help combat diseases in aquaculture.

Single and Multi-Strain Probiotics Supplementation in Commercially Prominent Finfish Aquaculture: Review of the Current Knowledge.

The Nile tilapia Oreochromis niloticus, Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, olive flounder Paralichthys olivaceus, common carp Cyprinus carpio, grass carp Ctenopharyngodon idella and rohu carp Labeo rohita are farmed commercially worldwide. Production of these important finfishes is rapidly expanding, and intensive culture practices can lead to stress in fish, often reducing resistance to infectious diseases. Antibiotics and other drugs are routinely used for the treatment of diseases and sometimes applied preventatively to combat microbial pathogens. This strategy is responsible for the emergence and spread of antimicrobial resistance, mass killing of environmental/beneficial bacteria, and residual effects in humans. As an alternative, the administration of probiotics has gained acceptance for disease control in aquaculture. Probiotics have been found to improve growth, feed utilization, immunological status, disease resistance, and to promote transcriptomic profiles and internal microbial balance of host organisms. The present review discusses the effects of single and multi-strain probiotics on growth, immunity, heamato-biochemical parameters, and disease resistance of the above-mentioned finfishes. The application and outcome of probiotics in the field or open pond system, gaps in existing knowledge, and issues worthy of further research are also highlighted.

Molecular characterization, antibacterial activity and mechanism analyzation of three different piscidins from black rockfish, Sebastes schlegelii

Sebastes schlegelii (black rockfish) is a popular and economically important fish species in aquaculture. However, disease outbreaks have hindered the development of its cultivation. Antimicrobial peptides (AMPs) are a group of important components in fish innate immune system, that are active in the first line of defense against pathogens. The piscidin family, which are a group of fish-specific AMPs, have been isolated in a part of teleost but still poorly understood in S. schlegelii. In this study, three piscidin genes (Ss-piscidin1, 2, 3) are identified in S. schlegelii and their antibacterial activities and related mechanisms are analyzed. Three Ss-piscidins have conserved signal peptides but highly variable mature peptides and prodomains, and their mature regions all have predicted amphipathic and α-helical structures. Phylogenetic analysis shows that three Ss-piscidins cluster with different fish piscidin sequences into three sister clades, which correspond to three groups of fish piscidin family, respectively. Ss-piscidins have constitutive expressions in different tissues of healthy fish and enhanced expressions after Aeromonas salmonicida challenge. All three piscidins exhibit antibacterial activities, and are able to enhance bacterial membrane permeability and change bacterial morphology to different degrees, with a positive correlation observed among these activities. This suggests that three peptides exert their antibacterial activity through a “membrane-attack” mechanism. Moreover, hemolytic activities of three piscidins are also analyzed, and Ss-piscidin1, with low hemolytic ability and high antibacterial activity, is considered to be a possible candidate template for design of AMP drugs. Results in this study can promote a better understanding of immune responses in black rockfish and facilitate the future development of strategies in fish disease control in aquaculture.

Adaptive Immune System in Fish

The immune system of all jawed vertebrates is composed of two major subsystems, the innate (non-specific) and adaptive (specific) immune system. The innate immune system is the first to respond to infectious agents; however, it does not provide longlasting protection. The adaptive immune system is activated later and responds to pathogens with specificity and memory. The main components of the adaptive immune system, including T cell receptors (TCRs), major histocompatibility complex (MHC), immunoglobulins (Igs), and recombination-activating gene (RAG) arose in the first jawed fish (cartilaginous and teleost fish). This review explores and discusses components of the adaptive immune system in teleost fish and recent developments in comparative immunology. Similar to mammals, the adaptive immune system in teleost fish is divided into two components: cellular-mediated responses and humoralmediated responses. T cells, the principal elements of cellular-mediated adaptive immune responses, differentiate into effector helper T (Th) cells or effector cytotoxic T cells (CTLs). The central elements involved in the differentiation of Th subsets in mammals, cytokines and master transcription factors, have also been identified in teleost fish. In addition, each subset of Th cells, defined with a particular cytokine to control the immune responses, has been described in teleost fish. Similarly, to mammals, CTLs contribute to cellular cytotoxicity in teleost fish. B cells act as a central player in humoral-mediated adaptive immunity by producing opsonizing, neutralizing and complement-binding antibodies and inducing antibody-dependent cellular cytotoxicity (ADCC). Three classes of antibodies named IgM, IgD, and IgT/Z have been characterized in teleost fish. The presence of an adaptive immune system and consequent immune memory in teleost fish allows vaccination, the most appropriate method for disease control in aquaculture. Immunological studies in fish provide a comprehensive assessment of the fish immune system, which is crucial for understanding the evolution of the mammalian immune system.

Review on probiotics as a functional feed additive in aquaculture

Aquaculture is emerging as one of the most viable and promising enterprises in providing nutritional and food security to humans. Intensification of the aquaculture practices has led to the increase in the stress level in the animal as well as in the environment. This has led to the outbreak of disease, causing huge loss in the aquaculture sector every year. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. However, the abuse of antimicrobial drugs, pesticides and disinfectants in aquaculture disease prevention and growth promotion has led to the evolution of resistant strains of bacteria. Hence the use of probiotics might be a good option to reduce the risk of disease and enhance the productivity. Probiotics thus are opening a new era in the health management strategy from human to aquatic species including fish and shellfish. Probiotics are beneficial bacteria that help in maintaining the well-being of the host animal. They directly or indirectly protect the host animal against harmful bacterial pathogens. This review summarizes and evaluates brief information regarding the use of probiotics in aquaculture.