Lake Berryessa copode parasites

The lesions are copode parasites. They seem to increase as water temps increase. You can scrap most of them off the skin when scaling the fish. They are not harmful to humans and generally don't affect the meat underneath the skin. They are just ugly to look at.

I never heard of these any problems with them? I guess they are only on the trout?

It really depends on the particular parasitic copepod.   For example, Argulus japonicus is an asian parasitic copepod that was introduced to the US from China and tends to infect freshwater ornamental fish like koi, goldfish and carp. 

There have been two types of parasitic copepods found in Lake Berryessa which were reported for the first time in 2000.  One in the genus Salmincola which infects only salmon and trout and another in the genus Lernea which can infect other fish as well. Interestingly, brook trout and brown trout are resistent to Salmincola while rainbow trout and pacific salmon suffer the infections.

Here's a link to an old DFG announcement I found http://www.dfg.ca.gov/news/news01/01068.html

Brian

Thaks Brian