THE USE OF SALT-SOLUTIONS TO CONTROL FUNGUS (SAPROLEGNIA) INFESTATIONS ON SALMON EGGS

The use of salt solutions in place of malachite green to control funga l infestations during salmonid egg incubation was studied from 1987 to 1989 in a series of experiments conducted at Robertson Creek Hatchery in Port Alberni, British Columbia. Several combinations of salt conce ntration (sea salt, NaCl, CaCl2), treatment length, and treatment freq uency were used on pre-eyed eggs of chinook salmon (Oncorhynchus tshaw ytscha). The efficacy of salt solutions was assessed against that of m alachite green by comparing the incidences of egg mortality and alevin abnormality. A solution containing a 26:1 mixture of sodium chloride and calcium chloride, applied at a concentration of 20 ppt for 60 min three times a week yielded mean egg mortalities of 6.2% (1988) and 9.7 % (1989). These results compared favorably with a malachite green trea tment of 1 ppm for 60 min applied three times a week that yielded mean egg mortalities of 5.2% (1988) and 8.8% (1989). Mortalities in salt t reatments of 25 ppt or of 120 min duration were attributed to toxic ov erdose. Mortalities in salt treatments of 10 ppt resulted from fungus infestation. Data suggested that malachite green treatments produced a higher incidence of alevin abnormalities than salt treatments. Future investigations into the use of salt solutions for fungus control shou ld consider the efficacy, logistics, and costs associated with treatme nt of large groups of eggs.