The in-vitro antibacterial effects of organic salts, chemical disinfectants and antibiotics against pathogens of black disease in fairy shrimp of Thailand.

The antibacterial effects of organic salts, chemical disinfectants and antibiotics were evaluated on cultures of Aeromonas hydrophila C03, Aeromonas sobria C26, A. sobria C29, Aeromonas caviae C24 and Acinetobacter sp. SH-94B, the pathogens that cause black disease found in fairy shrimps (Streptocephalus sirindhornae Sanoamuang et al. (2000) and Branchinella thailandensis Sanoamuang, Saengphan & Murugan) of Thailand. The minimal inhibitory concentrations (MICs) of organic salts (sodium chloride and potassium chloride) and antibiotics (oxytetracycline dihydrate, streptomycin sulphate, kanamycin monosulphate, chloramphenicol and ampicillin) were determined using the agar-dilution method. The effect of chemical disinfectants (sodium hypochlorite and chlorine dioxide) was evaluated by exposing bacteria to different concentrations of these chemicals for different periods of time. Interestingly, all strains were intrinsically resistant to 0.25-3% sodium chloride and potassium chloride. The effect of sodium hypochlorite was greater than that of chlorine dioxide, and 5-20 µg mL(-1) of sodium hypochlorite was sufficient to inhibit the growth of these bacteria, but the exposure time varied, depending on the bacterial species. Of the antibiotics tested, chloramphenicol and oxytetracycline dihydrate completely inhibited the selected strains. Chloramphenicol showed the highest antibacterial effect against all pathogenic species--the MIC and minimal bactericidal concentration (MBC) ranged from 0.8 to 3.1 µg mL(-1) from 3.1 to 6.25 µg mL(-1), respectively. To achieve control of black disease during cultivation of fairy shrimp, data derived from this study can be used as a basis for further toxicity tests in vivo.

Clinical observations of black disease in fairy shrimps, Streptocephalus sirindhornae and Branchinella thailandensis, from Thailand and pathogen verification.

In this study, black disease infecting fairy shrimps, Streptocephalus sirindhornae Sanoamuang, Murugan, Weekers & Dumont, and Branchinella thailandensis Sanoamuang, Saengphan & Murugan, in Thailand, was investigated. The typical signs of the disease are the appearance of black spots on the cuticle, located mainly on the dorsal side and thoracopods. A number of rod-shaped bacteria aggregated in the black spots and were visualized by scanning electron microscopy. The histopathological results showed that a haemocytic response to the infection resulted in a dense melanized core of bacteria. In addition, generalized septicaemia by rod-shaped bacteria was also observed in the infected tissue. Of the 31 isolates, Aeromonas spp. were predominantly isolated and six strains were selected for the experimental infections. The most pathogenic strain was identified molecularly as A. hydrophila. When fairy shrimp were infected at bacterial concentrations of 10(4) and 10(6) cfu mL(-1) , the overall infection levels were 73.33 ± 6.67% and 93.33 ± 6.67%, respectively. The experimentally infected fairy shrimp showed abnormal swimming and died within 24-48 h after the appearance of the dark pigment.

Exophiala xenobiotica infection in cultured striped jack, Pseudocaranx dentex (Bloch & Schneider), in Japan.

This report describes Exophiala infection in cultured striped jack, Pseudocaranx dentex, in Japan in 2005. One hundred out of 35,000 fish died per day and mortalities continued for 1 month. Diseased fish showed swelling of the abdomen and kidney distension. Numerous septate hyphae, pale brown in colour, were seen in kidney in squash preparations. Histology revealed abundant fungal hyphae and conidia in gill, heart and kidney. Fungal hyphae were accompanied by cell necrosis and influx of inflammatory, mainly mononuclear cells. The fungus isolated from the diseased fish had septate hyphae, pale brown in colour and 1.8-3.0 microm in diameter. Conidiogenous cells were conspicuous annellides, short or cylindrical or fusiform in shape. Conidia were one-celled, ellipsoidal with smooth walls, accumulated in balls at the apices of annellides that tended to slide down, 1.5-2.0 microm in width and 3.0-5.0 microm in length. The fungus was classified into the genus Exophiala based on its morphology and as Exophiala xenobiotica based on the sequences of the ITS 1-5.8S-ITS 2 regions of rDNA. This is the first record of this fungus in a marine fish.

Morphological and physiological characteristics of Saprolegnia spp. strains pathogenic to Atlantic salmon, Salmo salar L.

Seventeen strains of Saprolegnia spp. were examined for morphological and physiological characteristics, and seven were examined for their pathogenicity to Atlantic salmon, Salmo salar L. Two of the Saprolegnia strains tested caused 89 and 31% cumulative mortality in challenged salmonids and were significantly more pathogenic than the other strains tested. The positive control (Saprolegnia parasitica ATCC 90213) caused 18% mortality, but this was not significantly higher than non-pathogenic strains (0-3% cumulative mortality). All the pathogenic Saprolegnia strains and two non-pathogenic strains had secondary cysts with long, hooked hairs, a characteristic which is claimed to be typical of S. parasitica. This characteristic is apparently necessary, but does not in itself determine the ability to cause mortality in Atlantic salmon. However, all the pathogenic Saprolegnia strains in the present study showed a significantly higher initial growth rate of cysts in sterilized tap water than did non-pathogenic strains. The results of the present study suggest that initial growth rate of germinating cysts in pure water, together with the presence of long hooked hairs on the secondary cysts, may be indicators of pathogenicity of Saprolegnia strains to Atlantic salmon.

Fusarium incarnatum isolated from black tiger shrimp, Penaeus monodon Fabricius, with black gill disease cultured in Vietnam.

Fusarium incarnatum was isolated from gill lesions of cultured black tiger shrimp, Penaeus monodon, in every crop during 2000-2002 in Nghe An province, Vietnam. Infected shrimps showed typical signs of black gill disease and mortalities about a month prior to harvest. Detailed morphological examinations, as well as molecular phylogenic analyses based on partial nucleotide sequences of ribosomal DNA, were made on the isolates. An artificial infection of kuruma prawn, Penaeus japonicus, using two selected isolates was also conducted and their pathogenicity determined.

Saprolegniosis in salmonids and their eggs in Japan.

An epizootic of the fungal infection saprolegniosis that occurred in freshwater-cultured salmons and their eggs at some hatcheries in Hokkaido (Japan) was investigated. In almost all cases, the initial clinical sign was characterized by the growth of cotton-like mycelia on the fishs' body surface, especially the head, adipose fin, and caudal fin, but the mycelia were not visible to the naked eye in the internal organs. Thirty-three strains isolated from lesions were classified in the genus Saprolegnia according to their morphological and biological characteristics on hemp seed cultures at various temperatures. Fifteen of the strains were identified as Saprolegnia parasitica, 16 were identified as S. salmonis, and two were identified as S. australis.

Cladosporiosis in a tomato clownfish (Amphiprion frenatus).

Infection with Cladosporium sp., a deuteromycete, caused a deep dermal ulcer that extended to bone in a cultured tomato clownfish (Amphiprion frenatus). The infection may have been secondary to immunosuppression resulting from transport or confinement-induced stress or may have resulted from chronic exposure to copper. Reports of fungal infections in tropical marine fish are rare.

Dermatophytosis in a Steller sea lion (Eumetopias jubatus).

Serious dermatophytosis caused by Trichophyton mentagrophytes was found in a Steller sea lion (Eumetopias jubatus) at Yomiuri Land Marine Aquarium in Tokyo. The external clinical signs were extensive depilation and hyperkeratosis, as well as redness and depigmentation of the skin. Histopathological findings of the skin revealed PAS positive fungal hyphae with septa in the corneum layer of the epidermis. Further microscopic examination suggested that this lesion of the skin was typical chronic dermatophytosis. Based on morphological and growth characteristics, the isolate was identified as Trichophyton mentagrophytes. It was thought that the infection was due to some factors including species and individual specific and environmental factors and so on.

Mycotic gastritis of juvenile ayu (Plecoglossus altivelis) caused by Saprolegnia diclina type 1.

Histopathological and mycological studies were made on mycotic gastritis in juvenile ayu, Plecoglossus altivelis. The disease occurred 5 days after the transportation of fish from a hatchery pond to two rearing ponds of Tochigi Prefectural Fisheries Experiment Station, Tochigi, Japan. The pyloric region of the stomach was red. Numerous fungal hyphae penetrated into the stomach wall. Seven fungal isolates were obtained from the lesions. Three isolates were identified as Saprolegnia diclina Type 1. Based on histology, hyphae were most numerous in the pyloric stomach, but also penetrated abdominal adipose tissue, the pancreas, spleen, kidney, swim bladder, gonad, and liver. In some cases, the hyphae penetrated trunk muscles.

Mixed infection of an acid-fast bacterium and an imperfect fungus in a Napoleon fish (Cheilinus undulatus).

A Napoleon fish (Cheilinus undulatus) was infected with both an acid-fast bacterium and an imperfect fungus. This is the first report of an acid-fast bacterial infection in Cheilinus undulatus, and the first observation of an imperfect fungus in the swim bladder of a tropical marine fish.

Mass mortality in cultured coho salmon (Oncorhynchus kisutch) due to Saprolegnia parasitica coker.

Epizootics of saprolegniasis occurred in 20 to 60 g freshwater-cultured coho salmon (Oncorhynchus kisutch) in Miyagi Prefecture, Japan. Cotton-like mycelia occurred on the body surface of infected fish, especially around the head, the adipose fin and the caudal fin, and aseptate hyphae occurred in the lesions. The hyphae also penetrated into the muscle and blood vessels. The isolated fungus was identified by asexual morphological characteristics as Saprolegnia parasitica (syn. S. diclina Type 1), a known salmonid fish pathogen.

A visceral mycosis in cultured masu salmon (Oncorhynchus masou) caused by a species of Ochroconis.

Ochronconis sp. infection was found in masu salmon (Oncorhynchus masou) with visceral mycosis in Japan. The external and internal clinical signs were reddening of the anal area, swelling of the abdomen due to accumulation of ascitic fluid in the abdominal cavity and extensive swelling of the posterior kidney. Many pale brown, septate hyphae were found in the kidney by direct microscopical examination; these were usually not found in the other organs of infected fish. Histopathological examination of the kidney revealed large granulomas with the fungal hyphae and giant cells. The isolated fungus was identified as a species of the genus Ochroconis and was compared with O. tshawytschae, a known fish pathogen. Based on morphological and growth characteristics, we believe that these cases resulted from infection with a different species.