Using Non Target Species As a Biological Control for Parasitic Copepods

Maramec Spring Hatchery has been plagued with an infestation of the parasitic copepod Salmincola californiensis for many years, causing the hatchery’s production to be quarantined for use only in the Meramec River basin.  This parasite attaches to the mouth and gills of west slope and Pacific anadromous salmon and trout (Oncorhynchus spp.), including rainbow trout O. mykiss.  Although usually not fatal in wild trout populations, S. californiensis can be very prolific and detrimental in a hatchery.  Conditions at Maramec Spring provide the perfect environment for this copepod to proliferate and cause chronic mortalities as fish progress to larger sizes and infection rates reach 90%.   Following a study done in California, Maramec began using brook trout Salvelinus fontinalis as a biological filter for the parasite.  When the brook trout reached a sufficient density, we observed approximately an 80% reduction in infection.  Despite the success with the brook trout they were ultimately a dead end.  A unique follow up study was done using brown trout Salmo trutta in place of brook trout with similar results.  The brown trout are now used as a biological filter to reduce parasitic copepod infection on rainbow trout and to stock the Meramec River.