Studies on the inflammatory response of the striped snakehead Channa striatus (Fowler)

Experiments were carried out to define the cellular response of snakehead fish, Channa striatus (Fowler), to integumental ulceration: chronic granulomatosis associated with the standard irritant Freund's adjuvant; bacterial septic abscessation due to Aeromonas hydrophila , and focal exposure to the aquatic phycomycete Achlya debaryana. Following exposure, the pathogenesis of the resultant lesion was followed by means of histopathologlcal examination of sequentially sampled specimens. In the case of integumental ulceration, small artificially induced wounds had re-epithelialized within the remarkably short space of 2-3 hours after incision. Large numbers of macrophages were found throughout the degenerated muscle area at 4-5 hours but had completely disappeared from the area of defect by day 6-12. Small numbers of polymorphonuclear leucocytes were observed only at the very earliest stage after wounding. The wounded site was restored to normal condition by around 21-28 days. Chronic granulomata were invoked by injection with Freund’s complete adjuvant. Macrophage infiltration was particularly active in the early stages after the inoculation and started to decrease by day 21. It started to take on an epithelioid configuration within 24 hours of its development. Fibrosis and vascularization were seen at about the same time around day 4.The regeneration of myofibres had strongly developed by day 6 and the new muscle bundles had replaced the area of fibrosis almost completely by the 28th day. The granulomata lesions were still extant, albeit in a very modified, and highly fibrosed form, by the end of the experiment (11 weeks).The acute inflammatory response was demonstrated in the snakehead by injection with the bacterium, Aeromonas hydrophila. An ulcerative wound developed by day 2 after the inoculation. PMN showed a marked response to the bacterial infection and had infiltrated into the inflammatory area by the second hour after the injection. Bacterial colonies, found in the inflammatory area, were very closely related to these PMN clusters. Fibrosis started to encapsulate the necrotic area around 30-36 hours post injection. The lesion began to heal by day 7 to 10 and the healing process was completed around day 28. A very mild inflammatory response occurred in the snakehead injected with the fungus, Achlya debaryana. Some infiltrated PMN and lymphocytes migrated into the inoculated site at the early stages of the experiment, but macrophage activity dominated in the necrotic muscle area. Fibrosis, new capillaries, and regenerated muscle fibres were found by day 3-4 and the lesion was completely healed around day 6

Biodiversity of chloramphenicol-resistant mesophilic heterotrophs from Southeast Asian aquaculture environments

In the present study, samples of pond water, sediment and farmed species were collected at 12 fish and shrimp farms in Malaysia, Thailand and Vietnam to determine the biodiversity and environmental distribution of chloramphenicol-resistant (CmR) mesophilic heterotrophs in Southeast Asian aquaculture sites. Following isolation on Iso-Sensitest agar supplemented with 35 μg ml−1 Cm and dereplication using (GTG)5-PCR fingerprinting, 557 genotypically unique CmR strains were subjected to polyphasic identification. The 557 mesophilic heterotrophic CmR isolates represented 18 different genera largely dominated by the genera Escherichia (40.2%), Pseudomonas (11.7%), Acinetobacter (11.1%), Klebsiella (7.5%) and Bacillus (5.9%). A total of 439 CmR isolates were further assigned to 31 described species or species groups, mainly including organisms that have been associated with various human opportunistic infections such as Escherichia coli (n = 219), Pseudomonas putida (n = 47), Klebsiella pneumoniae (n = 38) and Acinetobacter baumannii (n = 23). Strains of Escherichia, and most notably, of E. coli, were the only common group of CmR heterotrophs irrespective of country, sample type or farm type. Together with other predominant but less widespread groups such as acinetobacters and pseudomonads, the results of this biodiversity study suggest that E. coli can be regarded as a potential indicator of Cm resistance in Southeast Asian aquaculture environments

Health management for sustainable aquaculture

Aquaculture is a dynamic activity. To be successful and sustainable in this business, new techniques have to be continually developed, and adopted by farmers. Over the last decade, sustainability has become a key word for many different activities, including aquaculture. Many factors are involved in aquaculture sustainability, and health management has an important role among these. In order for aquatic animal health management at the farm level to aid the achievement of optimum yields, the following issues should be considered: suitable site selection, quality of broodstock and seed, reasonable stocking density, feed and feeding programme, water management, prophylactic and therapeutic treatment, and information dissemination. The sustainability of aquaculture at the national and regional levels requires different considerations among which are national policy, assistance priorities for farmers, legislation needs, technology development, and information needs

Thailand

Meeting: Fish Quarantine and Fish Diseases in Southeast Asia, 7-10 Dec. 1982, Jakarta, IDIn IDL-773

Parasites of grouper (Epinephelus coioides) cultured in Thailand

Orange-spotted grouper (Epinephelus coioides) cultured in Thailand were examined for their parasites. There were five parasitic groups found in this investigation, viz., protozoans (four genera), monogeneans (five genera), digeneans (three genera), nematodes (two genera), and crustaceans (two genera). Two ciliated protozoans, Trichodina sp., Cryptocaryon irritans, and a single species of Amyloodinium sp. (flagellated protozoan) were observed externally on the gills and skin, while Sphaerospora sp. (myxozoan) was found to parasitize the kidney tubules of fish samples. Eight species of monogeneans were found, viz., Diplectanum grouperi, Pseudorhabdosynochus coioidesis, P. lantauensis, P. epinepheli, Haliotrema sp., two undescribed species of Pseudorhabdosynochus, Megalocotyloides sp. from the gills, and one species of monogenean, Benedenia epinepheli, from the skin. Digeneans, Aphanurus stossichi and Prosorhynchus pacifica, were found in the alimentary tract and a species of didymozoid, Gonapodasmius epinepheri, was present as yellow cysts attached to the gill filament. Two species of rare Philometra sp. and anisakid larva were observed on the body wall near the rectum and in the intestine, respectively. Two groups of crustaceans were found as external parasites, Caligus (copepod) and Rhaxanella (isopod). Monogeneans seemed to be major parasites of orange-spotted grouper in this study, which was indicated by great numbers and occurrence of Diplectanum epinepheli. There was no significant difference in parasite abundance among their own groups during the sampling period. Overall water quality parameters studied were stable, except transparency that fluctuated depending on the rainfall and tide. The occurrence of monogeneans showed correlation to water transparency. All fish samples showed no abnormal sign or symptom caused by parasitic infection

Epizootic ulcerative syndrome of fishes: rhabdovirus infection and EUS induction experiments in snakehead fish

Rhabdoviral agents have long been found to be associated with Epizootic Ulcerative Syndrome (EUS) although the presence of granulomas caused by the fungus Aphanomyces invadans is currently used as the diagnostic criterium of EUS. In the past few years, rhabdoviruses have been readily isolated from EUS-infected fish during the early period of some outbreaks in Thailand, but the role of viruses in EUS remained unclear. Rhabdovirus infection and EUS induction experiments were therefore conducted in this study. The rhabdovirus strain T9412 from EUS-diseased snakehead fish was used to infect healthy snakehead. The frequency of virus re-isolation from juvenile fish infected by a number of routes decreased to 50-75% on day 7, 0-50% on day 14 and 0-25% on day 30. The virus was more virulent at 20°C than 29°C, and caused death in snakehead fry with a LD50 equal to 2.16 Log10 TCID50/ml. EUS induction in juvenile snakehead fish was experimentally achieved using both rhabdovirus and Aphanomyces invadans type species RF-6. All (20/20) juvenile snakehead developed multiple EUS lesions by day 30 at 20°C when fish were first injected intramuscularly (i/m) with virus followed by bath challenge with fungal spores. Fish which received L-15 medium by injection and were then bathed with fungal spores also developed EUS lesions although, fewer (7/20) were affected. The rhabdovirus injection alone induced only small haemorrhagic wounds at the i/m injection site in some fish held at 20(C, and most wounds healed by the end of the experiment. A similar induction experiment conducted at 29(C failed to induce the EUS disease. Results of this study indicate that the rhabdovirus is lethal to snakehead fish fry at low temperature. The virus persists for only a short period of time in the juvenile fish and induces minor skin damage. Low temperature was found to be an important factor in facilitating the host fish to succumb to rhabdovirus and A. invadans infection in the laboratory. Therefore, one possible combination of events leading to EUS in snakehead fish is low temperature and the presence of rhabdovirus and Aphanomyces pathogens

Isolation of FV3-like iridovirus from a cutaneous ulceration disease of cultured frog, Rana tigrina Cantor, in Thailand

A new frog disease occurred in frog culture farms located in Central Thailand since early 1998. The disease affects 20-100% of the frog population in affected farms. Diseased adult frogs usually exhibit ulcerative lesions on the dorsal part of the body and legs with moderate mortality (20-50%). Some frogs had red lips, ulcerated mouths and rostrums. Diseased tadpoles and small frogs appeared weak with systemic inflammation. Mortality ranged from 50-100%. Histopathological changes observed include cutaneous ulceration and systemic inflammation with exuberant hematopoiesis. No bacteria could be isolated from the kidney, spleen and liver of frogs at the early stage of the disease. Viral investigation was, therefore, conducted. Seventy virus isolates were obtained from 107 diseased frogs collected from 8 provinces using the Epithelioma papulosum cyprini (EPC) cell line at 25°C. One virus isolate (AV9803) was partially characterized. The virions were enveloped, possessed genomic DNA and hexagonal nucleocapsid morphology, and were ~128 nm in diameter. The virus completely lost infectivity when incubated at 56°C for 30 min, in organic solvent or buffer pH 3. These findings indicate that this frog virus belongs to the family Iridoviridae. DNAs of 8 virus isolates from different provinces were extracted and compared using polymerase chain reaction or PCR. Similar sized PCR products were obtained using primers that were specific to different parts of a major capsid protein gene of Ranavirus type genus FV3. Over 99% nucleotide homology was observed between one sequenced PCR product of AV9803 and the sequence of FV3. These findings suggest that a single virus species was isolated which is most likely a strain of Ranavirus. This virus strain is temporally designated as Rana tigrina ranavirus (RTRV) . The RTRV seems to be associated with cutaneous ulceration. Further infection experiments and electron micrograph examinations in the diseased frog need to be done to confirm the causative agent

Important parasites of freshwater fish in Thailand and neighboring countries

Snakehead fish (Chana striata) from Thailand and Cambodia were sampled for parasitological study. The project was carried out from August 2003 to January 2004 twice a month. The results showed that there were 22 genera from 8 parasitic groups found externally and internally. The gill monogenean Trianchoratus pahangensis was found to be a dominant species, with in high degree of prevalence and intensity. Internal parasites from Cambodian fish samples, particularly Pallisentis nagpurensis (Acanthocephala), were observed in considerably greater abundance than those of Thai samples. Some parasite species, however, were common between the two sampling sites

Production and characterization of a monoclonal antibody against Aeromonas hydrophila

A monoclonal antibody (MAb), 8D10, was produced against Aeromonas hydrophila strain 94030 isolated from giant gourami (Osphronemus gourami). This was classified as an IgG2a immunoglobulin by ELISA, and recognised a 41 kDa band on whole cell preparations of the A. hydrophila by Western blotting. The reactivity of the MAb against twenty-five different A. hydrophila isolates was examined by an indirect ELISA and Western blotting. Twelve other bacterial species were also tested by the indirect ELISA to examine the specificity of the MAb. One of the A. hydrophila isolate (strain 95014) gave a strong reaction (89.9%) with the MAb in the ELISA and also recognised the 41 kDa band. Sixteen other strains were weak positive in the ELISA, and eleven of these strains were weakly positive by Western blotting. No cross-reaction with the non-A. hydrophila isolates occurred