Nilubol Kitancharoen

Streptococcus iniae, the Causative Agent of Mass Mortality in Rabbitfish Siganus canaliculatus in Bahrain

Abstract Streptococcus iniae was found to be responsible for mass mortality in whitespotted rabbitfish Siganus canaliculatus in Bahrain. External signs were listless swimming and dark coloration. Internally, ascites, hepatomegaly, and splenomegaly were observed. Identification of the bacterium was based upon biochemical, physiological, serological tests and DNA–DNA hybridization. Host susceptibility was examined in five fish species. Rabbitfish was the species most susceptible to streptococcal infection. Borneo mullet Liza macrolepis and brown-spot grouper Epinephelus coioides were also susceptible to the bacterium, whereas the seabream Acanthopagrus latus (known in Bahrain as black seabream) and one-spot bream Diplodus sargus were not.

Aquatic Fungi Developing on Eggs of Salmonids

Abstract Aquatic fungi isolated from salmonid eggs incubated at six fishery stations in Japan belonged to the genera Saprolegnia, Achlya, Aphanomyces, Leptolegnia, and Pythium. The species diversity of the fungi varied according to the site studied.

Fungicidal effect of hydrogen peroxide on fungal infection of rainbow trout eggs

Exposure to 1,500 μg/ml of hydrogen peroxide (H2O2) for 60 min at 13°C was found to be injurious to rainbow trout eggs. On the other hand, the concentration which effectively inhibited pathogenic fungi in vitro was substantially less than this toxic dosage; specifically, 500 μg/ml for 60 min at 20°C to inhibit the zoosporic stage and 1,000 μg/ml for 60 min at 20°C to inhibit the vegetative stage. From in vivo tests, treatment with 1,000 μg/ml of H2O2 for 60 min at 13°C was found to be the most effective procedure to control fungal infection and increase the hatching rate of rainbow trout eggs.

Some biochemical characteristics of fungi isolated from salmonid eggs

Fungal isolates from salmonid eggs displayed apparently unique patterns of biochemical characteristics at both the generic and specific levels. of the five genera examinedAchlya andPythium were able to assimilate 13–16 out of 19 carbohydrates.Aphanomyces was able to assimilate only glucose and starch, which was assimilated by all isolates. Members ofSaprolegnia displayed identical patterns of carbohydrate assimilation, except forS. hypogyna, which was also able to assimilate melibiose, in common withAchlya, Pythium, andLeptolegnia. Pythium was the only genus capable of assimilating salicin. OnlyAchlya andP. monospermum were able to assimilate rhamnose. In terms of amino acid assimilation isolates ofSaprolegnia ferax andS. diclina displayed an identical patterns, as did isolates ofS. parasitica andS. hypogyna. OnlyAphanomyces frigidophilus isolate was capable of assimilating cysteine. All genera exceptPythium assimilated glutamine, a fundamental amino acid. All isolates exhibited lipase and fatty acid esterase activities but no cellulase acitivity. The biochemical characteristics discovered in this study offer possibilities for identification and classification of these fungi, which are discussed herein.

Aphanomyces frigidophilus sp. nov. from eggs of Japanese char, Salvelinus leucomaenis

Aphanomyces frigidophilus sp. nov. was obtained from eggs of Japanese char,Salvelinus leucomaenis, from Tochigi Prefectural Fisheries Experimental Station, Utsunomiya, Japan. Vegetative hyphae were delicate, slightly wavy, moderately branched. Zoosporangia were isodiametric with the vegetative hyphae. Oogonia were abundant, originating on short stalks from lateral sides of hyphae. Oogonia were spherical, subspherical or pyriform, with a single subcentric oospore inside. Outer surfaces of oogonia were roughened with short papillate, crenulate or irregular ornaments. Antheridia and oospore germination were not observed. Zoospore germination and vegetative growth were found from pH 5.0 to 11.0. Zoospore production was highest at 10°C, whereas rapid growth occurred at 20–25°C. Vegetative growth of the fungus declined from the maximal level at 25°C to less than half maximal at 30°C and completely disappeared at 35°C.

Effects of pH and temperature on growth of Saprolegnia diclina and S. parasitica isolated from various sources

Saprolegnia diclina andS. parasitica isolated from three sources could germinate in strong acidic conditions. Growth ability correlated with the species of fungi rather than with the sources from which they were isolated.S.diclina isolates appeared to germinate at a pH condition as low as 3.5, whereasS. parasitica isolates could not germinate at below pH 3.8.S. parasitica isolates from visceral mycoses still showed good growth at 30°C, whereas other isolates did not. Also,S. parasitica isolates from visceral mycoses produced more abundant motile zoospores, and continued to do so for a longer period of time (28 d), thanS. parasitica isolates from external saprolegniasis andS. diclina isolates.

Atkinsiella awabi sp. nov. isolated from stocked abalone,Haliotis sieboldii

A fungal disease in the abalone,Haliotis sieboldii, stocked in Yamaguchi Prefecture, Japan, showed external signs of infection of tubercle-like swelling on the mantle and melanized lesions on the peduncle. The fungus responsible was isolated by inoculating materials taken from the lesions onto PYGS agar with streptomycin sulphate and ampicillin, and incubation at 20°C. For morphological observation and spore formation study, the fungus was transferred respectively into PYGS broth and sterilized artificial seawater and incubated at 20°C. Resulting, hyphae were stout, irregular, branched, 16–140µm diam, sporadically consisting of dense cytoplasmic swollen hyphae. Sporangia were formed through the formation of septa and lateral or terminal discharge tubes which were wavy or coiled. Zoospores were pyriform, biflagellate and diplanetic. The encysted spore generally developed a hairlike filament with globular enlarged tip in PYGS broth. Direct germination without filament formation also occurred occasionally. This fungus was identified as belonging to the genusAtkinsiella, and was designatedAtkinsiella awabi sp. nov. The fungus was exclusively a marine fungus and grew best in shrimp extract medium at 20°C. Five chemicals were tested for their effects against fungal zoospores.

A new record of Achlya klebsiana from snakehead, Channa striatus, with fungal infection in Myanmar.

This is the first record of the discovery in Myanmar ofAchlya klebsiana, belonging to the family Saprolegniaceae.

Morphological aspects of Saprolegnia diclina Type 1 isolated from pejerrey, Odonthetes bonariensis

Saprolegnia diclina Type 1 (syn.S. parasitica) discovered in pejerrey,Odonthetes bonariensis, is described and illustrated herein.

A marine oomycete Atkinsiella panulirata sp. nov. from philozoma of spiny lobster, Panulirus japonicus

A marine oomycete fungus was isolated from philozoma of the spiny lobster,Panulirus japonicus. The fungus exhibited slow growth, occasionally submerged, with a creamy white, raised moist colony. Hyphae were stout, arranged in radiating pattern, irregularly branched, 10–22 µm diam, occasionally separated by cross walls into subthalli. Thalli occasionally consisted of swollen features. Sporangia formed from the subthalli had 1–3 wavy or partly coiled discharge tubes at the terminal or subterminal area. Zoospores were pyriform or reniform, biflagellate, isokont and diplanetic. Encysted spores germinated as a hairlike filament with a globular enlarged tip in sterilized synthetic seawater, and directly as stout initial hypha in PYGS broth. This fungus was identified as belonging to the genusAtkinsiella and was designatedAtkinsiella panulirata sp. nov. The optimal temperature for the fungus was 25°C. Hyphal growth occurred in both sterilized synthetic seawater and NaCl in the range of 1.5–6.0% and 2.0–4.0%, respectively. The fungus could utilize all carbohydrates and derivatives tested as the carbon sources. From in vitro tests of five fungicides against the fungus malachite green was found to be the most effective.