In fish farming, high losses occur during egg incubation and larviculture due to diseases caused by oomycetes. This study aimed to identify the oomycete species that occurs in zebrafish Danio rerio eggs and to evaluate the oomyceticidal effect of copper sulfate, bronopol and methylene blue on the mycelial growth of this organism, as well as to determine the lethal and sublethal toxicity of these compounds in embryos of D. rerio. The isolates were cultivated in yeast-starch medium to determine the concentration necessary to inhibit mycelial growth by 50% (IC50) and 100% (minimum oomyceticidal concentration) after a 96 h exposure to these compounds. In addition, tests with D. rerio eggs were conducted to determine the lethal concentrations for 50% of the organisms (96h-LC50), and the concentrations that inhibited 17% of the eggs hatching (96h-IC17) after 96 h. The organism responsible for the mortality of D. rerio eggs was classified by classical and molecular methods as Aphanomyces brasiliensis, representing the first report of this pathogen in zebrafish eggs. IC50 values could be determined for both bronopol and copper sulfate, whereas methylene blue had low effectiveness against the oomycete. Copper showed high toxicity to D. rerio eggs at low concentrations, while methylene blue and bronopol toxicity was low and similar to each other. The use of bronopol at a concentration of 4.8 mg l-1 for the treatment of zebrafish eggs allows controlling the pathology without causing deleterious effects to the treated organisms.
We present herein the occurrence and distribution of the heterotrophic straminipiles collected from soil and water, submerged leaves and surface sediment from freshwater bodies at “Mosaico de Unidades de Conservação Juréia-Itatins”, a preserved conservation unit of the Brazilian Atlantic Rainforest. From 180 collected samples, we isolated 41 taxa belonging to Hyphochytriomycota and Oomycota using the multiple baiting technique, with several new taxa to the science, new occurrences to São Paulo State or Brazil, and all new citation to the studied area. These taxa were identified based on morphological and/or molecular data, with several genic regions made available in GenBank. The calculated community structure of these zoosporic organisms showed a diverse community, with few dominant taxa, without significant differences (P≤0.05) among the different types of samples.
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