Effectiveness of antifungal treatments during artificial incubation of the signal crayfish eggs (Pacifastacus leniusculus Dana. Astacidae)

Abstract

In artificial incubation of astacid crayfish eggs, the use of effective antifungal treatments is advisable for controlling the spread of fungi from dead to healthy eggs and increasing final efficiency rates. The aim of this study was to evaluate the effectiveness of formaldehyde, malachite green, hydrogen peroxide, isopropyl alcohol, copper sulfate, potassium permanganate and iodine (as polyvidone iodine) on signal crayfish (Pacifastacus leniusculus Dana) eggs incubated at 6.6 eggs/cm2 for long periods (up to 71 days). The administration of 3000 ppm formaldehyde for 15 min every other day up to the beginning of hatching allowed a stage 2 juvenile survival rate of 74.5%, without significant differences with 15 ppm malachite green (81.5%). These treatments did not show differences with the 150,000 ppm isopropyl alcohol dosage (65.5%). Formaldehyde at 3000 ppm can be administered up to the beginning of moulting to stage 2, without affecting the survival rates. Formaldehyde and malachite green treatments effectively controlled fungi. However, isopropyl alcohol and copper sulfate weakly inhibited mycelial growth only at the highest concentrations (150,000 and 18 ppm, respectively). Hydrogen peroxide below to 1500 ppm was insufficient to control fungi resulting in low survival rates to juvenile stage 2 (<22%). The potassium permanganate treatments (100 and 150 ppm) controlled fungi, but they were toxic to eggs. Iodine showed a light fungicidal effect being lethal to eggs at 10 and 20 ppm, whereas at 5 ppm survival efficiency to stage 2 juvenile was 54.1%. The losses between hatching and stage 2 in the treatments with the best results were around 30%, when stage 2 removal from incubators was carried out every other day. However, when the removal frequency increased (daily) these losses were reduced to 10%.