OTF, that is not true. I know this first hand after my pup found a trout head the had wife buried in a shallow grave; in the back yard. I know who I "won't" ask to help me bury a dead body! j/k..
He got really sick.
Only because I found his grave robbing adventures did we put the pieces together.
The salmon poisoning is actually a parasite, a worm called a fluke. Salmoniods returning to fresh water get them almost immediately. Trout being residents, consistently have them.
The treatment is two fold, one to mitigate the bacterial toxins from the flukes waste products. We used Rimfampin, which is similar to; if not the same compounds used for TB.
The second aspect of the treatment is for the fluke/ nematode itself.
Because this "illness" is parasitic/ bacterial, it can be contracted more than once.
So thoroughly cooked fish (salmoniods) would be safe. I never give my dogs any fish, more so because of the bones; same reason I don't give them bird scraps.