Why the Health Warnings for Brown Trout?

August 7, 2014

Question: In the fishing regulations there are safe eating guidelines for Donner Lake. I am trying to figure out why there are different recommendations for brown trout compared to rainbow trout. The guidelines suggest people eat only one serving of browns vs. seven servings of rainbows. Why? (Tim Worley)

Answer: The recommendations in our regulation booklet are from the Office of Environmental Health Hazard Assessment (OEHHA). The recommendations are probably from actual studies done by OEHHA of mercury levels in edible flesh from these two species from Donner Lake.

According to Dr. William Cox, California Department of Fish and Wildlife (CDFW) Program Manager of Fish Production and Distribution, we do not plant brown trout in Donner and so those fish are essentially wild and older in the system. Therefore, they have been on natural diets and accumulating mercury from the naturally occurring insects and aquatic life that comprises their food chain.

CDFW does plant rainbow trout in Donner as part of what we call a “put-and- take” fishery. For most of their lives those fish are not eating natural feeds, and are generally not piscivorous like the brown trout, so they accumulate much less mercury. Humans, especially children and women of child bearing ages, need to limit their intake of mercury because it can have serious health effects, including death.