Toxic effects in Aphanomyces brasiliensis and zebrafish embryos caused by oomyceticides

Abstract

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.

Occurrence and distribution of the heterotrophic straminipiles from Brazilian Atlantic Rainforest areas

“…All the identified taxa were isolated from freshwater and soil samples using baits as substrate. The majority of the species was found as saprotrophs, however some of them with pathogenic potential in plants and animals (Plaats-Niterink 1981, Sati 1991, Sandoval-Sierra & Diégues-Uribeondo 2015, Carraschi et al 2018, Ferreira et al 2021, Dima et al 2021, with several of them with genic regions made available for the first time in GenBank. Many of them have already mentioned for Brazil (Gomes & Pires-Zottarelli 2006, Mendes et al 1998, Miranda & Pires-Zottarelli 2008, Jesus et al 2013, b, 2018, however we contributed with new taxa for the science and new occurrences for the studied area, São Paulo State or Brazil.…”