The productivity in fish farming has been increasing and consequently the fish are submitted to high stocking densities which usually cause stress and immunosuppression. These conditions determine the occurrence of a series of infections, including saprolegniosis. This disease affects fish and eggs from freshwater determining relevant economic losses to fish farmers. Thus, to avoid outbreaks, are being sought effective chemical agents that are "environmentally friendly". The aim of this study was to evaluate the in vitro susceptibility of 12 isolates of Saprolegnia spp. from the silversides Odontesthes bonariensis and O. humensis. Susceptibility tests evaluating inhibition of mycelial growth of Saprolegnia spp. were performed using six chemicals (sodium chloride, formaldehyde, potassium permanganate, povidone-iodine, sea salt and iodized sea salt) in concentrations from 0 to 10,000ppm. The results displayed that formaldehyde at the concentration of 10ppm, and potassium permanganate at concentrations above 100ppm, were able to inhibit the mycelial growth of isolates of Saprolegnia spp. However, povidone-iodine and saline compounds exhibited no antimicrobial activity on Saprolegnia spp. Although the in vitro results showed that formaldehyde and potassium permanganate could be promising in controlling saprolegniosis, further studies should be performed to evaluate the in vivo efficacy of these compounds as well as to verify the toxicity of the chemicals to the silversides O. bonariensis and O. humensis.
Oomycetes; Odontesthes; saprolegniosis; chemical agents; susceptibility