170F-180F is way to hot to smoke fish.
Fish cooks at those temps.
Salmon comes out with that light orange color and is further insulted with that fugly whitish curd.
I know, I've done it with a Totem smoker (too many times)....that thing wants to run at 140 and it still cooks the fish at that temp.

Finally modded it with two Weber daisy wheel fresh air intakes and two 1-1/4" x 8" MC stacks.
I can now run at around 110F and produce professional-looking product.
My last smoke probably averaged 112F for about 14 hours.
Nice deep orange color with no fawking curd.

Another key is to air dry the fish after the brine and get good pellicle established before smoking.
Next I'm going to try a rub and no brine soak.

With a large smoker that runs too hot for fish you can also build a cold smoke box and pipe your exhaust through that.