Australia’s current biosecurity controls for importation of ornamental fish focus on post arrival quarantine. Various reviews, including a recent import risk analysis of freshwater ornamental fish on gourami iridovirus have identified a range of shortcomings. These shortcomings include that the current post-arrival inspection and quarantine isolation do not fully manage risks associated with fish that are sub-clinically infected, and that the current system does not adequately address risks posed by emerging diseases. To better meet its biosecurity obligations, the Department of Agriculture is reforming the current system by placing greater emphasis on managing biosecurity risks off-shore at source. At the heart of the new approach will be an on-arrival fish health surveillance system that aims to verify on-going compliance by overseas authorities in meeting Australia’s import requirements. Data collected by the surveillance system will provide for evidence-based decisions to address problems through government-to-government and industry channels. This could include the restriction or suspension of imports from high risk sources when non-compliance is not remedied. Importantly, the new approach will reward compliant exporters and importers, and allow the department to channel its resources to areas of greatest biosecurity risk. This biosecurity reform initiative represents significant change for both the government and industry. While some elements of the new system will be introduced in the near term, full implementation of the reforms, including the Fish Health Surveillance System, is likely to take some time.
IκBα (NF-κB inhibitor), Rab21 (Rab GTPase), and Rac2 (small GTP binding protein) play important roles in innate immunity. Previously, they were identified as differentially expressed immune-related genes in crucian carp Carassius auratus gibelio infected with Cyprinid herpesvirus 2 (CyHV-2) through suppression subtractive hybridization. Here, full-length IκBα, Rab21 and Rac2 cDNAs cloned from crucian carp showed high homologies with transcripts in other bony fish. These genes, usually expressed at low levels in all the examined crucian carp tissues, were significantly upregulated in kidneys from 6-24 h post-infection with CyHV-2 (P < 0.01) and from 6-72 h post-infection with A. hydrophila (P < 0.01). Thus, IκBα, Rab21 and Rac2 were involved in innate immunity to infection with CyHV-2 and A. hydrophila. The expression levels of IκBα and Rab21 in survived fish with viral infection were significantly higher than those in susceptible fish that had died from infection, but similar levels of Rac2 were observed in samples of surviving fish and moribund fish. These data suggested that crucian carp IκBα, Rab21, and Rac2 should share the same innate immune response to pathogen challenge with their mammalian homologues, and the differential expression level of IκBα and Rab21 between acute and chronic infection marked these two immune genes as markers for different infection outcomes.
MHC class I (MHC I) and Lysozyme C (LYZ C) play important roles in disease resistance in fish species, and are thought to participate in anti-viral innate immunity. Previously, after Cyprinid herpesvirus 2 (CyHV-2) infection, MHC I and LYZ C were found to be expressed in both moribund (acute infection) and survivor (chronic infection) fish based on suppression subtractive hybridization (SSH) analysis. Herein, the complete open reading frames (ORFs) of MHC I and LYZ C were cloned from crucian carp (Carassius auratusgibelio). The full-length cDNAs of these two genes contained ORFs of 1,038 and 438 bp, and encoded polypeptides of 345 and 145 amino acids, respectively. Phylogenetic analysis indicated that MHC I and LYZ C were most closely related to the common carp. We found that the two genes were expressed at low levels in all tissues examined in healthy crucian carp. The mRNA expression levels of MHC I and LYZ C in crucian carp kidney tissues was monitored at different time points for 72 h after CyHV-2 infection using real-time RT PCR analysis. During CyHV-2 infection experiments, peak levels of MHC I were observed at 72 hpi (5.55-fold, P < 0.01), whereas 48 hpi (3.87-fold, P < 0.01) was the peak expression time point for LYZ C. By analysis of samples from both acute and chronic infection, the expression levels of MHC I and LYZ C were up-regulated in comparison to uninfected fish. These data suggested that MHC I and LYZ C are involved in cellular response to CyHV-2 infection. The discovery of LYZ C induced by CyHV-2 in crucian carp suggests its potential role in fish innate immunity against viral pathogen as MHC I.
The present paper is a brief account of the diseases of carps and ornamental fish observed in Punjab. Six species of cultured cyprinids namely, Labeo rohita (rohu), Catla catla (catla), Cirrhinus mrigala (mrigal), Hypophthalmichthys molitrix (silver carp), Ctenopharyngodon idella (grass carp), Hypophthalmichthys noblis (bighead carp) and six ornamental fish species namely, Carassius auratus (goldfish, comet, shubunkin, oranda, black moor, fantail), Cyprinus carpio (koi carp), Poecilia reticulata (guppy), Poecilia sphenops (molly), Xiphophorus maculatus (platy) and Xiphophorus helleri (sword tail) were examined and were found to bear a range of mild to serious parasitic, fungal and bacterial infections. Parasitic infections were caused by: protozoans (i.e., Ichthyophthirius multifiliis, Trichodina sp., Chilodonella sp., Ichthyobodo sp., Piscinoodinium pillulare, Tetrahymena sp., Epistylis sp.); monogeneans (i.e., Dactylogyrus sp., D. vastator, D. extensus; Gyrodactylussp., G. turnbulli); digeneans (i.e., Posthodiplostomum cuticula; Cryptocotyle sp.), nematodes (i.e., Camallanus sp., Capillaria sp.); crustaceans (Lernaea cyprinacea, L. polymorpha, L. oryzophila, L. ctenopharyngodonis, Argulus foliaceus), and water mold/fungal infections (i.e., Saprolegnia sp., Achyla sp., Aspergillus spp., Penicillium sp., Alternaria sp., Mucor sp., Rhizopus sp., Blastomyces sp.). Bacterial diseases such as those responsible for motile aeromonad septicaemia, fin rot and hemorrhagic ulcers on skin are also reported from some carp and ornamental species. Lernaeasis was most prevalent disease in cultured carp; whereas the protozoan and monogenean infections were prevalent on ornamental fish.
Polycystic lesions have been reported in many different fish species. This paper reports for the first time a case of polycystic lesions in the liver of tilapia. A group of 700 tilapia juveniles of approximately 50 g was obtained from a hatchery in Negeri Sembilan, Malaysia. When they were between 130 and 250 g, they started to show distended abdomen but appetite remained normal. Post-mortem examination on 30 randomly selected tilapia revealed numerous large masses containing jelly-like material in the peritoneal cavity of 33% of the fish. Histopathology revealed typical cystic lesion of liver tissue. This is the first report in hybrid tilapia and is presumed to be the result of a genetic anomaly.
The first isolation of Vibrio vulnificus biotype I from disease outbreaks in cultured tiger grouper Epinephelus fuscoguttatus Forsskal, 1775 in southern Thailand has been described. Gross signs of diseased fish included dark coloration of body, anorexia, petechial hemorrhages in the skin of the tail and fins and ulceration of the skin. Hemorrhagic septicemia was observed in intestine, body cavity and spleen. The 205-bp amplified DNA fragment of the hemolysin gene (vvhA) was detected from all of bacterial isolates, indicating V. vulnificus. Bacteria showed characteristics of biotype 1, the human clinical isolate, as indicated by their motility, positive results for indole production, ornithine decarboxylation activity, acid production from D-mannitol and growth at 42°C. The human virulence potential of V. vulnificus isolates using three biomarkers, 16S ribosomal ribonucleic acid (rRNA), vvhA gene and virulence-correlated gene (vcg), showed that genotypes of V. vulnificus was the clinical-type with two profiles. The susceptibility of tiger grouper to V. vulnificus isolate was performed by intraperitoneal injection (i.p.) with 106 CFU/mL bacterial suspensions. The experimentally injected tiger grouper had mortalities within 5 days post-injection and developed clinical signs similar to those found in disease outbreak. In a vaccination trial, the tiger grouper vaccinated with formalin inactivated whole-cell vaccine exhibited relative percent survival (RPS) of 68% following homologous isolate challenge. In conclusion, V. vulnificus biotype 1 strain that caused disease in tiger groupers is similar to V. vulnificus pathogenic to humans.
Water samples from randomly selected shrimp hatcheries were enumerated for mean total Vibrio count (MTVC) while obtaining mean percentage of cumulative mortality (MPCM) for different larval stages. Pathogenecity of Vibrio isolates was studied on mysis larvae and post larvae by challenging with four concentrations (102 to 105 CFU mL-1). Significantly higher MTVC was recorded for broodstock maturation and spawning tanks. Artemia hatching tanks had the highest MTVC (1.67 × 104 CFU mL-1). Feeding mysis with Artemia nauplii, increased MTVC significantly in mysis tanks. Artemia nauplii and broodstocks are the major sources of contamination. MTVC in rearing water were positively related to MPCM of larvae. The most common species of Vibrio were V. parahaemolyticus, V. alginolyticus, V. harveyi, V. vulnificus and V. fluvialis; pathogenecity of former three species were greater on mysis II, the most pathogenic being V. parahaemolyticus (97.5% MPCM at 48 hours post challenge with 105 CFU mL-1). V. alginolyticus was the most pathogenic species to Pl12 (77.75% MPCM) followed by V. harveyi and V. parahaemolyticus. All five species showed varying degree of resistance to the tested antibiotics. In order to control pathogenic Vibrio and to reduce larval mortality, strict bio-security measures and best management practices are recommended.
Iridovirus is a serious aquatic virus infecting variable species of fish and frog. Development of a rapid, reliable detection method is an important issue for commercial and scientific purposes. With specific anti-body-functionalized magnetic nanoparticles, viruses can be bound immunologically and quantitatively detected by measuring the related magnetic signals. Immunomagnetic reduction (IMR) is a technique to measure the magnetic signals change in this work. Using this assay, the low-detection limit of iridovirus was found 101 TCID50/mL. There was no significant interference from the other grouper viruses including nervous necrosis virus (NNV). The iridovirus concentration in grouper detected with IMR was 91% related to real-time polymerase chain reaction (real-time PCR). These results demonstrated the feasibility of IMR on iridovirus screening in grouper.
Shrimp (Penaeus monodon) culture accounts a large proportion of Bangladesh’s aquaculture industry by value, and is the country’s second largest source of export earnings. But it has encountered enormous problems due to the spread of diseases, particularly white spot disease (WSD), and has incurred significant economic losses as a result. The major factors encouraging WSD outbreaks are the production of post larvae (PL) using wild broodstock and traditional farming systems with poor farm level bio-security. Between 2005 and 2014 WorldFish tested broodstock, nauplii and PL from hatcheries in Bangladesh using polymerase chain reaction (PCR) technique, as part of a program to supply white spot syndrome virus (WSSV) free PLs to project farmers. A strong positive correlation (R = 0.743) was found among WSSV infected broodstock and WSSV infected nauplii, providing evidence of transmission of WSSV from mother to PL in hatcheries. On an average, every year almost 36.19% of hatchery produced PL was found to be WSSV positive considering positive nauplii batches from 2005 to 2014. This would be sufficient to contaminate almost the entire farming system, as 88% of farming area is under traditional farming practice. Developing commercial PCR testing facilities for ensuring supply of WSSV free seed and implementing farm level bio-security programs could reduce disease risks, improve farm productivity and contribute to country’s economy.
In order to determine the aetiology of cultivable freshwater carp mortalities of Northeast Indian states, we analysed infected fish samples by virus isolation using cell cultures and virus detection by PCR. The fishes collected from Manipur had typical ulcerative dermal lesions resembling epizootic ulcerative syndrome (EUS). Samples from Northeast India were analysed by PCR and ranaviral major capsid protein specific DNA was detected in one of the 66 tissue samples collected from 12 infected fish (kidney of Puntius sarana) of Assam and nine out of 15 infected Osteobrama belangeri samples of Manipur. Sequence analysis of a 289 bp fragment of one of the amplified DNA from infected fishes of Northeast India showed 98.9% homology with the major capsid protein gene of koi ranavirus (KJ939444), which we earlier isolated from infected koi that were undergoing mortalities and characterised to belong to Ranavirus genus of the family Iridoviridae. Our results have revealed the presence of ranavirus in freshwater fishes suffering from mortalities in Northeast India. As ranaviruses are known for their genomic adaptive changes facilitating host shift between fish, amphibian and reptilian hosts, there is a need to pay attention to the spread of emerging ranavirus infection in fishes.
Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli were isolated from wild and cultured fish (18 striped catfish, Pangasianodon hypophthalmus, and 18 red tilapia, Oreochromis sp.) in the Mekong Delta, Vietnam, from June 2014 to October 2014. In total, 39% of the fish harbored ESBL-producing E. coli, including 44.4% of wild fish and 36.1% of cultured fish. The E. coli isolates were highly resistant to ampicillin, cefotaxime, trimethoprim-sulfamethoxazole, and nalidixic acid among the antibiotics tested. Cephalexin (4/16, 25%), cefazolin (1/16, 6%), enrofloxacin (1/16, 6%), sulfadimidine (3/16, 19%), and sulfamethoxazole (15/16, 94%) were detected in water samples obtained at the fish collection sites. These results showed that the sampled fish harbored ESBL-producing E. coli, suggesting that fish are a potential source of human pathogens and mediate interspecific transfer of antimicrobial-resistant genes.
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