Fish Health

Fish managers have become increasingly concerned about fish health during the 1980s and 1990s. This increased focus on fish health was primarily due to the well-publicized chinook salmon die-off (epizootic) that occurred in Lake Michigan during the late 1980s. Holey et al. (1998) reported a 50% or more reduction in chinook salmon abundance due to spring die-offs caused primarily by BKD. Although the exact reasons for the spring epizootics of the late 1980s are still being debated, this mortality led to a reduction in fishing effort of more than 50% by 1995 and substantial economic loss. Another fish-health concern, early mortality syndrome (EMS), created significant egg-hatchability problems for Lake Michigan coho salmon (Honeyfield et al. 1998b). Survival of coho salmon eggs to the first-feeding-fry stage has been poor in state fish-culture facilities since the early 1990s (Trudeau 1995). By 1995, mortality of coho salmon eggs was so high that there was not enough hatchery space to incubate the eggs required to meet production goals.