Formalin treatments before eyeing and hand-picking of Arctic charr (Salvelinus alpinus) eggs – re-evaluating the timing of antifungal treatments

Arctic charr (<i>Salvelinus alpinus</i>) eggs in hatcheries are treated for fungal infections using formalin before, and hand-picking during the eyed stage. The relative effectiveness of the treatments was evaluated using a factorial design with the application of weekly hand-picking, and formalin treatments at 380 ppm for 13 minutes three times weekly as factors. The effects of the treatments on total mortality and hatching success were compared using a two-way ANOVA. Both treatments exhibited significant, positive effects on egg survival. Hand-picking during the eyed stage (+ 0.5 to 2.5 % survival to hatch) was found to be more effective than formalin treatments before (+ 0.0004 to 0.8 % survival to hatch). This is likely due to differences in the timing of administration of the treatments. The probability of fungal infections is indicated to vary with time, and a peak seemed to occur at hatch.