When king salmon enter the Yukon River on their spawning migration in mid June, over 25% of the population are infected with Ichthyophonus. The percent of infected fish remains relatively constant until the fish pass river mile 1,319 at Dawson, Y.T., then it drops to 13% when they reach river mile 1,745 at Whitehorse, Y.T. When the sexes are examined separately, slightly more females are infected than males (29% vs 22%). The percent of fish exhibiting clinical signs (diseased) is 2-3% when they enter the river, but increases to over 20% at river mile 715 near Tanana, AK. Disease prevalence within the population remains constant at > 20% until fish pass Dawson, then the percent of diseased fish drops to < 9% at Whitehorse. When the [...]
