Antifungal activity of sodium chloride on Saprolegnia diclina and Aphanomyces sp.

Abstract

Sixteen identified and three unidentified species belonging to six genera of zoosporic fungi were isolated from forty water samples which were collected from different fish and fish hatcheries farms at Abbassa city, Sharkiya governorate, Egypt, using sesame seeds baiting technique at 20±2°C. Saprolegnia and Achlya contributed the broadest spectra of species diversity amongst the other genera of zoosporic fungi. Saprolegnia diclina and Aphanomyces sp. were the most prevalent species of zoosporic fungi. The abundance of zoosporic fungal species in these aquacultures was correlated with some physicochemical characteristics of the water samples. The two dominant species of zoosporic fungi were tested for their tolerance of NaCl solution and its impact on some morphological and metabolic activities of these fungi. Saprolegnia diclina tolerated concentrations of NaCl solution till 12000 μg/ml whereas the maximum resistance of Aphanomyces sp. was 8000 μg/ml. The examined morphological aspects of the two studied fungal species, which included the colony diameters, the vegetative hyphae, zoosporogenesis, zoospores discharge, sexual reproductive structures and gemmae formation, were generally affected depending upon the tested fungal species and the applied dose of NaCl solution. The low treatments of NaCl solution were significantly stimulative compared with the control for protease production by S. diclina but higher doses were significantly suppressive. A significant decline in protease activity at all applications was found when Aphanomyces sp. was treated with NaCl solution. The total free amino acids and total protein content of S. diclina and Aphanomyces sp. mycelia were almost significantly increased relative to untreated controls at the low dose of NaCl solution and they were significantly dropped at the higher concentrations by the two zoosporic fungi.