Use of Formalin during Incubation of Eyed Eggs of Inland Fall Chinook Salmon

Abstract The influence of daily formalin treatments on eyed egg and fry mortality was evaluated during the incubation of eyed eggs of inland fall chinook salmon Oncorhynchus tshawytscha. A 3–5% increase in survival was observed in trays of eggs treated with formalin at 1,667 mg/L for 15 min daily from egg eye-up until just before hatch compared with incubation trays from which dead eggs were manually removed to control Saprolegnia. Egg survival in trays receiving both daily formalin treatments and manual egg removal did not differ significantly from those trays receiving only formalin treatments. Significant reductions in mortality were observed prehatch when formalin was used, and there was no difference in mortality from hatch to fry swim-up. Both formalin treatments and the hand-picking of dead eggs adequately controlled visible fungal development from egg eye-up to hatching.