Histopathological changes of Korea cultured olive flounder, Paralichthys olivaceus due to scuticociliatosis caused by histophagous scuticociliate, Philasterides dicentrarachi

Identification of Philaster apodigitiformis in aquaculture and functional characterization of its β-PKA gene and expression analysis of infected Poecilia reticulata

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is a distinctive member of the serine–threonine protein AGC kinase family and an effective kinase for cAMP signal transduction. In recent years, scuticociliate has caused a lot of losses in domestic fishery farming, therefore, we have carried out morphological and molecular biological studies. In this study, diseased guppies (Poecilia reticulata) were collected from an ornamental fish market, and scuticociliate Philaster apodigitiformis Miao et al., 2009 was isolated. In our prior transcriptome sequencing research, we discovered significant expression of the β-PKA gene in P. apodigitiformis during its infection process, leading us to speculate its involvement in pathogenesis. A complete sequence of the β-PKA gene was cloned, and quantified by quantitative reverse transcription-polymerase chain reaction to analyse or to evaluate the functional characteristics of the β-PKA gene. Morphological identification and phylogenetic analysis based on small subunit rRNA sequence, infection experiments and haematoxylin–eosin staining method were also carried out, in order to study the pathological characteristics and infection mechanism of scuticociliate. The present results showed that: (1) our results revealed that β-PKA is a crucial gene involved in P. apodigitiformis infection in guppies, and the findings provide valuable insights for future studies on scuticociliatosis; (2) we characterized a complete gene, β-PKA, that is generally expressed in parasitic organisms during infection stage and (3) the present study indicates that PKA plays a critical role in scuticociliate when infection occurs by controlling essential steps such as cell growth, development and regulating the activity of the sensory body structures and the irritability system.

Formulation of chitosan microsphere-based oral vaccine against the scuticociliate parasite Miamiensis avidus: Evaluation of its protective immune potency in olive flounder (Paralichthys olivaceus)

Miamiensis avidus is a parasitic pathogen that causes scuticociliatosis, a severe and often lethal marine infection that affects marine fishes worldwide, including olive flounder (Paralichthys olivaceus) in Korea. This parasite infects all size groups of flounder year-round, causing recurring mortalities and huge economic losses to the Korean flounder industry each year. However, few efforts have been made to implement effective remedial measures to control this parasite. Therefore, our study sought to develop a chitosan microsphere (MS)-encapsulated inactivated vaccine (IMa + chitosan) for oral delivery (adsorbed in feed) to flounder fingerlings and assess its protective efficacy at different modalities via three in vivo experimental trials. Immunisation trial-1 was conducted to determine the effective concentration of chitosan. Our findings indicated that an IMa + chitosan 0.05 % vaccine formulation was safe and effective in providing moderate protection [46.67%-53.3 % relative percent survival (RPS)] against M. avidus intraperitoneal (IP) injection challenge at two weeks post-vaccination (wpv) compared to the IMa + chitosan 0.01 % and IMa + chitosan 0.005 % vaccines (0%-13.3 % RPS) irrespective of the antigen doses. In trial-2, the IMa + chitosan 0.05 % vaccine elicited similar protective immunity (30.8%-57.1 % RPS) in olive flounder against M. avidus at varying antigen doses (high: 2.38 × 106 cells/fish; low: 1.5 × 105 cells/fish), immunisation periods (2 and 5 wpv), and challenge modes (IP injection and immersion). Furthermore, experimental trial-3 validated the use of chitosan MS as an IMa antigen carrier to improve survivability (41.7 % RPS) in the host by significantly (p < 0.05) upregulating specific anti-M. avidus antibody titres in the fish sera and mucus of the group immunised with IMa-containing chitosan MS. In contrast, non-specific immunomodulatory effects (16.7 % RPS and enhanced mucosal antibody titres) were observed in the group treated with chitosan MS without IMa. Therefore, our findings suggested that oral administration of chitosan MS (0.05 %)-encapsulated IMa vaccine is a promising immunisation strategy against M. avidus that can protect the IMa antigen from digestive degradation, facilitates its targeted delivery to the host immune organs, and helps in orchestrating protective immune induction in olive flounder, thus controlling parasite infection.

Characterization of the complete mitochondrial genome of Miamiensis avidus causing flatfish scuticociliatosis

Miamiensis avidus is a parasitic pathogen that causes the disease scuticociliatosis in teleost fish species. It is a ciliate and a free-living marine protozoan belonging to the order Philasterida, subclass Scuticociliatida, class Oligohymenophorea, and phylum Ciliophora. The complete mt-genome of M. avidus was linear and 38,695 bp in length with 47 genes, including 40 protein-coding genes, two ribosomal RNA (rRNA) genes, and five transfer RNA (tRNA) genes. Of these, 20 genes typically belong to the clusters of orthologous groups, playing roles in energy production and conversion, translation, ribosomal structure and biogenesis, and defense mechanisms. This is the first report of sequencing and characterization of the mt-genome of M. avidus, which was observed to be linear and possessing the typical ciliate mitochondrial genome organization and phylogenetic relationships. Remarkable differences were observed between M. avidus and other ciliates in the mitochondrially encoded rRNAs, extensive gene loss in ribosomal genes and tRNAs, terminal repeat sequences, and stop codon usage. A comparative and phylogenetic analysis of M. avidus and Uronema marinum of the order Hymenostomatida, which is most closely related to the order Philasterida, signified the promise of the mitogenome data of M. avidus as a valuable genetic marker in species detection and taxonomic research. The present study has potential applications in epidemiological studies and host-parasite interaction investigations facilitating disease control.

Efficacy of Chitosan-PLGA encapsulated trivalent oral vaccine against viral haemorrhagic septicemia virus, Streptococcus parauberis, and Miamiensis avidus in olive flounder (Paralichthys olivaceus)

The present study was conducted to assess the protective efficacy of a trivalent oral vaccine containing chitosan-PLGA encapsulated inactivated viral haemorrhagic septicemia virus (VHSV), Streptococcus parauberis serotype I and Miamiensis avidus antigens, followed by its oral (incorporated in feed) administration to olive flounder (Paralichthys olivaceus) fingerlings for a period of 15-consecutive days. After 35 days of initial vaccination, three separate challenge studies were conducted at the optimal temperature of the targeted pathogens using an intraperitoneal injection route. RPS analysis revealed moderate protection in the immunized group against all the three pathogens viz., VHSV (53.30% RPS), S. parauberis serotype-I (33.30% RPS), and M. avidus (66.75% RPS), as compared to the respective non-vaccinated challenge (NVC) control group. In addition, the immunized fish demonstrated significantly (p < 0.05) higher specific antibody titres in serum and significant (p < 0.05) upregulation in the transcript levels of immune genes of Igs (IgM, IgT, pIgR), TLRs (TLR 2, TLR 7), cytokines (IL-1β, IL-8) and complement pathway (C3) in the mucosal and systemic tissues than those of NVC control fish, suggesting orchestration of pathogen-specific host immune responses thereby favouring its combativeness against the three pathogens. The expression dynamics of IFN-γ, Mx, caspase 3 genes post VHSV challenge; IFN-γ, TLR 2, caspase 1 genes post S. parauberis serotype I challenge and CD-8α, IL-10, TNF-α genes post M. avidus challenge further substantiates the efficacy of the vaccine in stimulating antiviral, antibacterial and antiparasitic immune responses in the host resulting in their better survival. The findings from the present study reflect that the formulated trivalent oral vaccine incorporating VHSV, S. parauberis serotype I and M. avidus antigens can be a promising prophylactic strategy to prevent the associated disease outbreaks in olive flounder.

Scuticociliatosis caused by Philasterides dicentrarchi

The ciliate Philasterides dicentrarchi has been previously identified as a new agent of scuticociliatosis in marine fish. The parasite can cause high mortalities in fish reared on farms or kept in aquariums. P. dicentrarchi is usually a free-living protozoan but can become an opportunistic histophagous parasite causing rapid lethal systemic infections in cultured fish. This review provides information about the morphology and biology of the scuticociliate P. dicentrarchi, as well as information about the pathological and immunological reactions of the host in response to the infection with the parasite. The epidemiology and the control strategies of the disease are also reviewed.

Potential Efficacy of Chitosan-Poly (Lactide-Co-Glycolide)-Encapsulated Trivalent Immersion Vaccine in Olive Flounder (Paralichthys olivaceus) Against Viral Hemorrhagic Septicemia Virus, Streptococcus parauberis Serotype I, and Miamiensis avidus (Scuticociliate)

Olive flounder (Paralichthys olivaceus) is the most valuable aquaculture species in Korea, corresponding to ~60% of its total production. However, infectious diseases often break out among farmed flounders, causing high mortality and substantial economic losses. Although some deleterious pathogens, such as Vibrio spp. and Streptococcus iniae, have been eradicated or contained over the years through vaccination and proper health management, the current disease status of Korean flounder shows that the viral hemorrhagic septicemia virus (VHSV), Streptococcus parauberis, and Miamiensis avidus are causing serious disease problem in recent years. Furthermore, these three pathogens have differing optimal temperature and can attack young fingerlings and mature fish throughout the year-round culture cycle. In this context, we developed a chitosan-poly(lactide-co-glycolide) (PLGA)-encapsulated trivalent vaccine containing formalin-killed VHSV, S. parauberis serotype-I, and M. avidus and administered it to olive flounder fingerlings by immersion route using a prime-boost strategy. At 35 days post-initial vaccination, three separate challenge experiments were conducted via intraperitoneal injection with the three targeted pathogens at their respective optimal temperature. The relative percentages of survival were 66.63%, 53.3%, and 66.75% in the group immunized against VHSV, S. parauberis serotype-I, and M. avidus, respectively, compared to the non-vaccinated challenge (NVC) control group. The immunized fish also demonstrated significantly (p < 0.05) higher specific antibody titers in serum and higher transcript levels of Ig genes in the mucosal and systemic tissues than those of NVC control fish. Furthermore, the study showed significant (p < 0.05) upregulation of various immune genes in the vaccinated fish, suggesting induction of strong protective immune response, ultimately leading to improved survival against the three pathogens. Thus, the formulated mucosal vaccine can be an effective prophylactic measure against VHS, streptococcosis, and scuticociliatosis diseases in olive flounder.

Functional characterization and gene expression profile of perforin-2 in starry flounder (Platichthys stellatus)

The membrane attack complex/perforin (MACPF) superfamily consists of multifunctional proteins that form pores on the membrane surface of microorganisms to induce their death and have various immune-related functions. PFN2 is a perforin-like protein with an MACPF domain, and humans with deficient PFN2 levels have increased susceptibility to bacterial infection, which can lead to fatal consequences for some patients. Therefore, in this study, we confirmed the antimicrobial function of PFN2 in starry flounder (Platichthys stellatus). The molecular properties were confirmed based on the verified amino acid sequence of PsPFN2. In addition, the expression characteristics of tissue-specific and pathogen-specific PsPFN2 mRNA were also confirmed. The recombinant protein was produced using Escherichia coli, and the antimicrobial activity was then confirmed. The coding sequence of PFN2 (PsPFN2) in P. stellatus consists of 710 residues. The MACPF domain was conserved throughout evolution, as shown by multiple sequence alignment and phylogenetic analysis. PsPFN2 mRNA is abundantly distributed in immune-related organs such as the spleen and gills of healthy starry flounder, and significant expression changes were confirmed after artificial infection by bacteria or viruses. We cloned the MACPF domain region of PFN2 to produce a recombinant protein (rPFN2) and confirmed its antibacterial effect against a wide range of bacterial species and the parasite (Miamiensis avidus).

Interactions between the Parasite Philasterides dicentrarchi and the Immune System of the Turbot Scophthalmus maximus. A Transcriptomic Analysis

The present study analyses the interactions between Philasterides dicentrarchi (a ciliate parasite that causes high mortalities in cultured flatfish) and the peritoneal cells of the turbot Scophthalmus maximus during an experimental infection. The transcriptomic response was evaluated in the parasites and in the fish peritoneal cells, at 1, 2 and 4 h post-infection (hpi) in turbot injected intraperitoneally (ip) with 10⁷ ciliates and at 12 and 48 hpi in turbot injected ip with 10⁵ ciliates. Numerous genes were differentially expressed (DE) in P. dicentrarchi, relative to their expression in control ciliates (0 hpi): 407 (369 were up-regulated) at 1 hpi, 769 (415 were up-regulated) at 2 hpi and 507 (119 were up-regulated) at 4 hpi. Gene ontology (GO) analysis of the DE genes showed that the most representative categories of biological processes affected at 1, 2 and 4 hpi were biosynthetic processes, catabolic processes, biogenesis, proteolysis and transmembrane transport. Twelve genes of the ABC transporter family and eight genes of the leishmanolysin family were DE at 1, 2 and 4 hpi. Most of these genes were strongly up-regulated (UR), suggesting that they are involved in P. dicentrarchi infection. A third group of UR genes included several genes related to ribosome biogenesis, DNA transcription and RNA translation. However, expression of tubulins and tubulin associated proteins, such as kinesins or dyneins, which play key roles in ciliate division and movement, was down-regulated (DR). Similarly, genes that coded for lysosomal proteins or that participate in the cell cycle mitotic control, glycolysis, the Krebs cycle and/or in the electron transport chain were also DR. The transcriptomic analysis also revealed that in contrast to many parasites, which passively evade the host immune system, P. dicentrarchi strongly stimulated turbot peritoneal cells. Many genes related to inflammation were DE in peritoneal cells at 1, 2 and 4 hpi. However, the response was much lower at 12 hpi and almost disappeared completely at 48 hpi in fish that were able to kill P. dicentrarchi during the first few hpi. The genes that were DE at 1, 2 and 4 hpi were mainly related to the apoptotic process, the immune response, the Fc-epsilon receptor signalling pathway, the innate immune response, cell adhesion, cell surface receptors, the NF-kappaB signalling pathway and the MAPK cascade. Expression of toll-like receptors 2, 5 and 13 and of several components of NF-κB, MAPK and JAK/STAT signalling pathways was UR in the turbot peritoneal cells. Genes expressing chemokines and chemokine receptors, genes involved in prostaglandin and leukotriene synthesis, prostaglandins, leukotriene receptors, proinflammatory cytokines and genes involved in apoptosis were strongly UR during the first four hours of infection. However, expression of anti-inflammatory cytokines such as Il-10 and lipoxygenases with anti-inflammatory activity (i.e., arachidonate 15-lipoxygenase) were only UR at 12 and/or 48 hpi, indicating an anti-inflammatory state in these groups of fish. In conclusion, the present study shows the regulation of several genes in P. dicentrarchi during the early stages of infection, some of which probably play important roles in this process. The infection induced a potent acute inflammatory response, and many inflammatory genes were regulated in peritoneal cells, showing that the turbot uses all the protective mechanisms it has available to prevent the entry of the parasite.

Two short antimicrobial peptides derived from prosaposin-like proteins in the starry flounder (Platichthys stellatus)

Prosaposin (PSAP) is a precursor of saposin (SAP), which is present in lysosomal and secreted proteins. PSAP is a member of the SAP-like protein families, which comprise multifunctional proteins. In particular, their antimicrobial activity has been reported. We identified PSAP-like (PsPSAPL) sequences from starry flounder and analysed their expression and antimicrobial activity based on cDNA and amino acid sequences. PsPSAPL showed conservation of three saposin B type domains at high levels, and PsPSAPL mRNA was relatively abundantly distributed in the brain and gills of healthy starry founders. PsPSAPL mRNA showed significant expression changes in response to viral haemorrhagic septicaemia virus and Streptococcus parauberis. Synthetic peptides (PsPSAPL-1 and -2), prepared based on amino acid sequences, were used to confirm as well as analyse the antimicrobial activity against bacteria and parasites. Consequently, PsPSAPL-1 and -2 were found to significantly inhibit the growth of various bacteria and kill the Miamiensis avidus. In addition, bacterial biofilm formation was significantly inhibited. Safety was also confirmed by analysing cell haemolysis. These results indicate the immunological function of PsPSAP and the potential antimicrobial activity of the AMPs PsPSAPL-1 and -2.

Scuticociliatosis caused by Uronema sp. in ten different ornamental aquarium reef fish in Brazil

Scuticociliatosis, caused by an opportunistic ciliate protozoan, is responsible for significant economic losses in marine ornamental fish. This study reports the occurrence of Uronema spp., parasitizing ten species of marine reef fish at an ornamental fish wholesaler: Blue green damselfish (Chromis viridis), Vanderbilt's Chromis (Chromis vanderbilti), Pennant coralfish (Heniochus acuminatus), Threespot angelfish (Apolemichthys trimaculatus), Goldspotted angelfish (Apolemichthys xanthopunctatus), Sea goldie (Pseudanthias squamipinnis), Orchid dottyback (Pseudochromis fridmani), Threadfin butterflyfish (Chaetodon auriga), Vagabond butterflyfish (Chaetodon vagabundus), and Bluecheek butterflyfish (Chaetodon semilarvatus). Diseased fish showed disorders such as hemorrhages and ulcerative lesions on the body surface. Histopathological analysis of the muscle, liver, gut, kidney, spleen, gills, and stomach revealed hemorrhages and degeneration of muscle fiber, vacuolar degeneration of hepatocyte, inflammatory process and granuloma in the liver, atrophy of intestinal villi, inflammatory process and granuloma in the kidney, melanomacrophage centers, as well as inflammatory process in the spleen, epithelial cells hyperplasia and granuloma formation in the gills, and vacuolar degeneration and eosinophils in the stomach. Due to the severity of the disease, it is necessary to implement biosecurity measures with rapid and accurate diagnosis to minimize the risk of economic losses caused by Uronema spp.

Genome based quantification of Miamiensis avidus in multiple organs of infected olive flounder (Paralichthys olivaceus) by real-time PCR

INTRODUCTION

Miamiensis avidus is the major parasitic pathogen affecting the olive flounder, Paralichthys olivaceus. Recent epidemiological studies have shown that M. avidus infections are becoming increasingly severe and frequent in the olive flounder farming industry.

OBJECTIVES

This study aimed to evaluate the infection density of M. avidus in various organs of the olive flounder including spleen, liver, kidney, stomach, esophagus, intestine, gill, muscle, heart, and brain. Olive flounders were collected from a local fish farm.

METHODS

Each fish was injected subcutaneously with 2.75 × 10³ CFU M. avidus/ fish. Organs infected with M. avidus were obtained after 7 and 25 days. Each organ was examined for parasitic infection using real-time PCR. The primers were designed according to the sequences of 28 s in M. avidus, which was used as a target gene.

RESULTS

Each organ was examined for parasitic infection using real-time PCR. The primers were designed according to the sequences of 28 s in M. avidus, which was used as a target gene. The levels of 28 s rRNA were used to calculate quantitative gene copy number. Real-time PCR of brain (60.58 ± 38.41), heart (64.03 ± 62.40), muscle (6.10 ± 3.12), gill (5.06 ± 4.56), intestine (2.38 ± 1.69), esophagus (4.22 ± 3.72), stomach (3.25 ± 2.68), kidney (0.81 ± 0.15), liver (0.63 ± 0.15), and spleen (11.18 ± 4.08) was performed at 3 days post-infection. At 7 days post-infection, heart (754.15 ± 160.85), brain (247.90 ± 62.91), spleen (38.81 ± 17.52), liver (7.47 ± 4.54), kidney (10.90 ± 3.41), stomach (19.50 ± 8.86), esophagus (39.37 ± 14.10), intestine (17.54 ± 12.63), gill (38.27 ± 20.20), and muscle (33.62 ± 15.07) were measured.

CONCLUSION

The present study, together with previous data, demonstrated that the gill, intestine, and brain are the major target organs of M. avidus in olive flounder. However, this does not mean that tiny amounts of DNA extracted from those tissues of fish during the early stages of infection can guarantee successful detection and/or quantification of M. avidus. Our data suggest that the brain might be the best organ for detection in the early stage.

Locally extensive meningoencephalitis caused by Miamiensis avidus (syn. Philasterides dicentrarchi) in a zebra shark

Scuticociliatosis, caused by ciliated protozoa in the subclass Scuticociliatia of the phylum Ciliophora, can cause fatal disease in teleost fish species. However, information on scuticociliatosis in elasmobranchs is still scarce. In this report, we describe a case of locally extensive meningoencephalitis caused by Miamiensis avidus (syn. Philasterides dicentrarchi) in a 2 yr old captive zebra shark Stegostoma fasciatum. Granulocytic meningoencephalitis was observed through histological assessment. Inflammation was confined to the ventral aspect of the brain with a large number of ciliated protozoa, transforming into non-suppurative meningitis in the lateral aspect, and gradually vanished in the dorsal aspect. No histopathological and polymerase chain reaction (PCR) evidence of systemic dissemination of M. avidus was found. PCR targeting the gene coding the small-subunit ribosomal RNA (SSUrRNA) of M. avidus was performed on the brain, liver, and gill tissues, and only brain tissue yielded a positive result. The DNA sequences from amplicons of the protozoal SSUrRNA gene were completely matched to that of M. avidus. The distribution of protozoa in the current case was mainly located in the brain and suggests the possibility of a direct neural invasive pathway of M. avidus through the nasal cavity/ampullary system and/or a unique tissue tropism of M. avidus specific to the brain in zebra sharks. Further investigations on the pathogenesis of M. avidus in elasmobranchs, especially zebra sharks, are needed.

First report of scuticociliatosis caused by Uronema sp. in ornamental reef fish imported into Brazil

Abstract Scuticociliatosis, which is caused by an opportunistic ciliate protozoan, is responsible for significant economic losses in marine ornamental fish. This study reports the occurrence of Uronema sp., which was found to be parasitizing three species of marine reef fish imported into Brazil and maintained in quarantine: Vanderbilt’s Chromis (Chromis vanderbilti), blue-green damselfish (Chromis viridis), and sea goldie (Pseudanthias squamipinnis). During the quarantine period, some fish presented with behavioral disorders and hemorrhages and ulcerative lesions on the body surface. Histopathological analysis showed hemorrhages, inflammation comprising mononuclear and granular cells in the skeletal muscle, and necrosis of the skin and the secondary lamellae of the gills, and parasites were also observed in the renal capsule. The absence of transboundary measures available to prevent the occurrence of ornamental fish diseases is also discussed.

Combination treatment against scuticociliatosis by reducing the inhibitor effect of mucus in olive flounder, Paralichthys olivaceus

The olive flounder, Paralichthys olivaceus, is an economically important food fish in Japan and Korea. Scuticociliatosis is a major parasitic disease, and fatal infection with scuticociliates, or mixed infections with scuticociliates and other pathogenic agents (e.g., Vibrio spp.) cause severe mortalities in farmed olive flounders. To date, however, effective chemotherapeutic treatment of scuticociliatosis has only been reported at the in vitro level. In this study, we employed combination treatment, using benzalkonium chloride (to remove excess mucus from the body surface) and bronopol (to kill the parasites), to overcome the protective effect of mucus by some medicine to the scuticociliates. In the presence of the mucus mixture, the higher dose of bronopol (156 ppm) yielded morphologies and motilities similar to those of ciliates treated with the lower dose of bronopol (80 ppm) in the absence of mucus. We also investigated the in vivo effects of this treatment in field trials involving a total of 15,025 naturally infected flounders. We observed that short-term bath treatments with benzalkonium chloride (50 ppm) followed by bronopol (500 ppm) were effective, assessed by the relative percentage mortality (RPS) value. Thus, this study provides a notable therapeutic strategy by removing the mucus to treat scuticociliatosis in olive flounders at the aquaculture field level.

Delineating cellular interactions between ciliates and fish by co-culturing Tetrahymena thermophila with fish cells

Although several species of Tetrahymena are often described as histophagous and opportunistic pathogens of fish, little is known about ciliate/fish cell interactions, but one approach for studying these is in vitro with cell lines. In this study, T. thermophila, B1975 (wild type) and NP1 (temperature sensitive mutant for phagocytosis) were cultured on monolayers of 3 fish epithelial cell lines, CHSE-214, RTgill-W1, and ZEB2J, and the rabbit kidney epithelial cell line, RK-13. Generally the ciliates flourished, whereas the monolayers died, being completely consumed over several days. The destruction of monolayers required that the ciliates could make contact with the animal cells through swimming, which appeared to dislodge or loosen cells so that they could be phagocytosed. The ciliates internalized into food vacuoles ZEB2J from cell monolayers as well as from cell suspensions. Phagocytosis was essential for monolayer destruction as monolayers remained intact under conditions where phagocytosis was impeded, such as 37°C for NP1 and 4°C for B1975. Monolayers of fish cells supported the proliferation of ciliates. Thus T. thermophila can 'eat' animal cells or be histophagous in vitro, with the potential to be histophagous in vivo.

Reprint of "fish immunity to scuticociliate parasites"

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined.

Expression and characterization of cathepsin L-like cysteine protease from Philasterides dicentrarchi

Philasterides dicentrarchi is a causative agent of scuticociliatosis in olive flounder Paralichthys olivaceus, aquaculture in Korea. In this study, a cDNA encoding a cathepsin L-like cysteine protease (PdCtL) of P. dicentrarchi (synonym Miamiensis avidus) was identified. To express the PdCtL recombinant protein in a heterologous system, 10 codons were redesigned to conform to the standard eukaryotic genetic code using polymerase chain reaction (PCR)-based site-directed mutagenesis. The recombinant P. dicentrarchi procathepsin L (proPdCtL) was expressed at high levels in E. coli Rosetta (DE3) pLysS with a pPET21a vector, and successfully refolded, purified, and activated into a functional and enzymatically active form. The optimal pH for protease activity was 5. Similar to other cysteine proteases, enzyme activity was inhibited by E64 and leupeptin. Immunogenicity of recombinant PdCtL was assessed by enzyme-linked immunosorbent assay, western blot, and specific anti-recombinant PdCtL antibodies were detected. Our results suggest that the biochemical characteristics of the recombinant ciliate proPdCtL protein are similar to those of the cathepsin L-like cysteine protease, that the PCR-based site-direct mutated ciliate gene was successfully expressed in a biochemically active form, and that the recombinant PdCtL acted as a specific epitope in olive flounder.

Fish immunity to scuticociliate parasites

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined.

Effect of orally administered azadirachtin on non-specific immune parameters of goldfish Carassius auratus (Linn. 1758) and resistance against Aeromonas hydrophila

Modulation of the immune responses using active bio-ingredients as a possible prophylaxis measure has been novel prospect for aquaculture. The present study evaluated the effects of azadirachtin EC 25% on non-specific immune responses in goldfish Carassius auratus and resistance against pathogenic bacteria Aeromonas hydrophila. The experimental trial for effects of azadirachtin on immuno-haematoloical parameters in goldfish was conducted by feeding the various levels of azadirachtin as control T(0) (without azadirachtin), T(1) (0.1%), T(2) (0.2%), T(3) (0.4%), T(4) (0.8%) and T(5) (1.6%) for a period of 28 days. Fishes were challenged with A. hydrophila 28 days post feeding and relative percentage survival (%) was recorded over 14 days post infection. Immuno-haematoloical (total erythrocyte count, total leukocyte count, haemoglobin, packed cell volume, NBT activity, phagocytic activity, serum lysozyme activity, myeloperoxidase activity, total immunoglobulin) and serum biochemical parameters (serum glutamate oxaloacetate transaminase (SGOT), serum glutamate pyruvate transaminase (SGPT) and blood glucose) of fishes were examined at 14 and 28 days of feedings. Fish fed with azadirachtin, showed significantly (p < 0.05) enhanced TEC, TLC, Total Ig, total protein, NBT activity, serum lysozyme activity and myeloperoxidase level in different treatment groups in comparison with control group. Similarly, SGOT, SGPT and blood glucose level were found to be significantly (p < 0.05) high but PCV and Hb did not differ significantly (p > 0.05) in the treatment groups compared to control groups. Azadirachtin at the concentration of 4 g kg(-1) showed significantly (p < 0.05) higher relative percentage survival (42.60%) when compared with the control against A. hydrophila infection. This study indicated that azadirachtin EC 25% (4 g kg(-1)) showed higher NBT activity, serum lysozyme, protein profiles, leukocyte counts and resistance against A. hydrophila infection and thus, can be used as a potential immunostimulant in aquaculture.

Injuries and deformities in fish: their potential impacts upon aquacultural production and welfare

Fish can be the recipients of numerous injuries that are potentially deleterious to aquacultural production performance and welfare. This review will employ a systematic approach that classifies injuries in relation to specific anatomical areas of the fish and will evaluate the effects of injury upon production and welfare. The selected areas include the (1) mouth, (2) eye, (3) epidermis and (4) fins. These areas cover a large number of external anatomical features that can be injured during aquacultural procedures and husbandry practices. In particular, these injuries can be diagnosed on live fish, in a farm environment. For each anatomical feature, this review addresses (a) its structure and function and (b) defines key injuries that can affect the fish from a production and a welfare perspective. Particular attention is then given to (c) defining known and potential aquacultural risk factors before (d) identifying and outlining potential short- and long-term farming practices and mitigation strategies to reduce the incidence and prevalence of these injuries. The review then concludes with an analysis of potential synergies between risk factors the type of injury, in addition to identifying potential synergies in mitigation strategies. The paper covers both aquaculture and capture-based aquaculture.

Turbot resistance to Philasterides dicentrarchi is more dependent on humoral than on cellular immune responses

Philasterides dicentrarchi is a ciliate that causes high mortalities in cultured turbot, Psetta maxima (L.). This pathogen displays high phagocytic activity and after entering the body it multiplies and feeds on host cells and tissue components. In previous studies, we found that complement, activated through the classical pathway, is a potent killer of P. dicentrarchi. Here, we compared the killing activity of turbot leucocytes and humoral factors against two virulent isolates of P. dicentrarchi, in order to determine the importance of leucocytes in the defence against this pathogen. Components of P. dicentrarchi (ciliary and membrane) stimulated turbot leucocytes, and increased the respiratory burst, degranulation and the expression of pro-inflammatory cytokines. We tested the susceptibility of ciliates to reactive oxygen and nitrogen species, by incubating them with different oxidative systems (H(2)O(2), Fe/ascorbate, which induces lipid peroxidation, an O(2)(-) donor (XOD/HX), an NO donor (SNAP) and an ONOO(-) donor (SIN-1)), for 24h. Both isolates were susceptible to high concentrations of H(2)O(2,) Fe/ascorbate, XOD/HX, and SIN-1 but were resistant to incubation with SNAP. Leucocytes became strongly activated when they were in contact with or were phagocytosed by the ciliate. Incubation of P. dicentrarchi with a combination of fresh serum and specific antibodies killed most of the ciliates, but the addition of leucocytes to ciliate cultures did not increase the toxicity to the ciliates. On the contrary, the number of ciliates increased when leucocytes were added to the culture because the ciliates fed on them. Despite being activated, leucocytes did not produce sufficiently high concentrations of toxic substances to kill the parasite. The most virulent isolate was that which induced greatest activation of leucocytes but was least susceptible to complement. We concluded that humoral factors such as complement (activated through the classical pathway) are critical for fish defence against P. dicentrarchi and that cellular responses appear to play a minor role, if any, in defence against this ciliate.

Protective effect of herbal and probiotics enriched diet on haematological and immunity status of Oplegnathus fasciatus (Temminck & Schlegel) against Edwardsiella tarda

This study determines the effect of diet enriched with the herb Baical skullcap Scutellaria baicalensis, and/or probiotics Lactobacillus sakei BK19 in rock bream, Oplegnathus fasciatus (32 ± 3 g) against Edwardsiella tarda. The changes in haematological parameters, innate immune response, and disease resistance were investigated after 1, 3, and 6 weeks. The white blood cell count (WBC: 10(4) mm(-3)), red blood cell count (RBC: 10(6) mm(-3)), and haemoglobin (Hb: g dl(-1)) levels significant increased (P < 0.05) with mixed diet on 3rd and 6th week and probiotics enriched diet on 6th week. The haematocrit (Ht: %) level significantly increased (P < 0.05) when fed with mixed diet on weeks 1-6. Interestingly, in mixed diet group the lymphocytes (LYM), monocytes (MON), and neutrophils (NEU) significantly increased from week 1-6. The eosinophils (EOS) significantly increased in all the treated groups. In the probiotics or mixed diet groups the total protein (TP: g dl(-1)) increased significantly on weeks 3 and 6. The serum lysozyme activity significantly was enhanced in all the treated groups indicating an increase in the innate immunity level. Serum complement, antiprotease activities, reactive oxygen species (ROS) and reactive nitrogen species (RNS) production significantly increased from week 1-6 with mixed diet. The maximum protection against E. tarda was recorded in mixed diet group with a minimum cumulative mortality of 20% and a high relative percent survival (RPS) of 72.84. In the probiotics and herbal diet groups the cumulative mortality was 25% and 35% and RPS was 68.63 and 59.42, respectively. This study indicates that administration of probiotics or mixed diets can effectively minimize the mortality and restore the altered hematological parameters and enhancing the innate immunity in O. fasciatus against E. tarda.

Immunomodulatory effect of probiotics enriched diets on Uronema marinum infected olive flounder

The effect of five probiotics, Lactobacillus plantarum, Lactobacillus acidophilus, Lactobacillus sakei, Bacillus subtilis, and Saccharomyces cerevisiae as individual and mixed enriched diet on the seasonal prevalence, activity and intensity of Uronema marinum infection in olive flounder Paralichthys olivaceus is reported. The growth performance, feed efficiency, blood biochemistry, survival rate, and non-specific immune response of U. marinum infected olive flounder on week 0, 1, 2, 4, 6, and 8 were quantified. The prevalence and infection intensity reached a peak from June to December and then it declined from December to March. The scuticocidal activity in the serum was significantly higher when fed with L. plantarum, L. acidophilus, and S. cerevisiae diets on weeks 2-8. All enriched diets significantly enhanced the weight gain significantly between week 6 and 8; the feed efficiency registered a significantly increase from week 4 to 8 when compared to infected fish fed with control diet. Infected fish fed with L. plantarum-supplemented diet had higher survival rate than with other enriched diets. The serum aspartate aminotransferase (GOT) and alanine aminotransferase (GPT) levels significantly increased when fed with L. plantarum, L. acidophilus or S. cerevisiae-supplemented diet. Total protein (TP) and glucose (GLU) level significantly increased with any enriched diet from week 4 to 8. The superoxide anion production and serum lysozyme activity registered a significant increase when fed with L. plantarum, L. acidophilus, and S. cerevisiae-supplemented diet from week 4-8. The present study concludes that L. plantarum, L. acidophilus, and S. cerevisiae-supplemented diets act as immunostimulants enhancing the growth, feed efficiency, blood biochemistry, survival rate, and non-specific immune response in U. marinum infected olive flounder.

Dietary administration of Zooshikella sp. enhance the innate immune response and disease resistance of Paralichthys olivaceus against Sreptococcus iniae

We report the growth, innate immune response, and disease resistance in olive flounder (Paralichthys olivaceus) challenged with Streptococcus iniae after feeding with diet enriched with Zooshikella sp. strain JE-34 three different concentration i.e. Low (3.4 x 10(4), n = 50), medium (3.5 x 10(6), n = 50), and high (3.4 x 10(8), n = 50) cfu ml(-1) supplemented diets, the changes were monitored on weeks 1, 2, 4, 8, 12, and 16. With all diets the innate immune parameters, such as superoxide anion production, phagocytic and lysozyme activity were not enhanced on week 1 and 4. On the other hand, all tested immune parameters in the treated groups significantly enhanced after 8th week; the weight gain significantly increased after 4th week in fish fed with enriched diets. The mortality in olive flounder after administration with high concentration diet showed 25%. With low and medium enriched diets the mortality was 40% and 35%, respectively. In the infected untreated group mortality was 85% while there was no mortality in the control group. The results suggested that Zooshikella sp. strain JE-34 enriched diets could be used to enhance the innate immune response and disease resistance of P. olivaceus against S. iniae.

Scuticociliatosis and its recent prophylactic measures in aquaculture with special reference to South Korea Taxonomy, diversity and diagnosis of scuticociliatosis: Part I Control strategies of scuticociliatosis: Part II

Scuticociliatosis caused by about 20 species belonging to the Phylum Ciliophora has been recognized as an emerging problem inflicting significant economic loss in aquaculture industry in the world. Among these Philasterides dicentrarchi, Miamiensis avidus, and Uronema marinum are the three species responsible for scuticociliatosis in olive flounder farms of South Korea. Some of the parasites living or scavenger ciliates also have become parasites of aquaculture fish. The major clinico-pathological manifestations of scuticociliatosis infected fishes are anemia, weight loss, dark coloration, enteritis, excessive body mucus, yellowish intestinal mucus, loss of scales, hemorrhagic and/or bleached spots on the skin, and dermal necrotic lesions that finally destroy tissues lead to high mortalities. Affected fish exhibit organ-specific pathological changes in the brain, eyes, muscle, gills, liver, kidney, intestine, and stomach that lead to severe mortality. At present, farmers in South Korea manage scuticociliatosis by using therapeutic measures, such as application of antibiotics like oxytetracycline, gentamycine, tetracycline, amoxycililin, and cefazolin and chemicals, such as formalin, hydrogen peroxide, malachite green, and jenoclean at a concentration of 350 +/- 150 ppm. However till date, no systematic scientific study has been conducted under field condition on the efficacy of these management measures. Under laboratory condition the ciliate can be effectively controlled with the antibiotics and chemicals while on the host, but on entering the host no systemic chemotherapeutic treatment has been yet proven effective. Furthermore the indiscriminate uses of harmful chemicals in aquaculture are increasingly becoming a cause of concern. Recently formalin and malachite green, the most widely used chemicals have been banned in food fish production by FDA as not consumer friendly and being carcinogenic respectively. Vaccines and immunostimulants can induce good immune response and protect against scuticociliatosis as it has been proved in the case of freshwater Ich. Now a days a number of probiotics and herbal formulations are in use against freshwater bacterial and fungal diseases, while, little information is available regarding the different prophylactic measures against marine scuticociliatosis. This review attempts to provide information on the various prophylaxic measures practiced against scuticociliatosis with special reference to olive flounder farms in South Korea.