Effects of different antifungal treatments on artificial incubation of the astacid crayfish (Pacifastacus leniusculus Dana) eggs

During the artificial incubation, fungi can grow over nonviable eggs and invade the healthy ones causing a decrease of efficiency rates. Thus, the use of antifungal substances must be considered. Different doses and treatment frequencies of formaldehyde, hydrogen peroxide, sodium chloride and malachite green were tested on eggs of signal crayfish (Pacifastacus leniusculus Dana). Eggs were incubated at two densities: 2.2 and 6.6 eggs/cm2. The highest efficiency to stage 2 juvenile (67.3%) was obtained with formaldehyde (4500 ppm) applied for 15 min three times a week up to the beginning of hatchings, without significant differences with the same treatment applied twice a week neither with malachite green (15 ppm). In both cases, the fungal growth was effectively inhibited. The formaldehyde dose of 1500 ppm administered every 3 days, as well as hydrogen peroxide and sodium chloride treatments, were insufficient to control fungi. It was detected a positive effect when density was reduced, so that with 2.2 eggs/cm2, a final efficiency of 71% was obtained even without antifungal use; while with 6.6 eggs/cm2, it was 22.6%.