USE OF FORMALIN DURING INCUBATION OF EYED EGGS OF INLAND FALL CHINOOKSALMON

The influence of daily formalin treatments on eyed egg and fry mortali ty was evaluated during the incubation of eyed eggs of inland fall chi nook 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 m in daily from egg eye-up until just before hatch compared with incubat ion trays from which dead eggs were manually removed to control Saprol egnia. Egg survival in trays receiving both daily formalin treatments and manual egg removal did not differ significantly from those trays r eceiving only formalin treatments. Significant reductions in mortality were observed prehatch when formalin was used, and there was no diffe rence in mortality from hatch to fry swim-up. Both formalin treatments and the hand-picking of dead eggs adequately controlled visible funga l development from egg eye-up to hatching.