It's a dead fish 100%. Same reason stated above. Dead stare, open mouth, flared bottom of the mouth, indents where it was placed on rocks.
My opinion is that it is a steelhead.
It has:
- Visible rows of radiating spots on the tail
- Tail rays fanning out in the middle of the tail only
- Heavy spotting in rows on the dorsal from top to bottom
- Spotting on the adipose
- Short maxilla that doesn't extend past the eye
- A very short and deep anal fin, which is squared off rather than angled
I have never seen a coho with spotting like that on the full tail (small radiating spots from base to end in perfect rows), nor have I seen a coho with colourful tail rays in that particular fashion. Normally coho with tail rays look like this:
and not like this (which is what that picture appears to have):
I have also never seen a coho with that many small perfect spots below the lateral line. Coho tend to have larger spots mixed with the small spots, and they typically stay above the lateral line.
Lastly, it is incredibly rare to have any sort of dorsal spotting on a coho, especially one that chrome. That is also coupled with the adipose spots (dorsal and adipose spots are clearly visible in that picture).
The only dorsal spotting I have seen on coho is like this (irregular and large spots):
Not small spots that are again, in perfect radiating rows like steelhead have:
If I have seen spots on coho adipose/dorsal fins, they are typically not numerous (as they are on that fish), and are generally on only one or the other.
Just my opinion. Take it for what it's worth.
I would also like to add, that I would love to see people's pictures of coho with numerous spots on the tails, dorsals, and adipose fins. I just went through well over 300 photos and only found maybe a dozen coho with spots on the dorsals (and the one I pictured had the most by a long shot). I found none with full tail spotting. I also found none with both distinct adipose AND dorsal spotting. It would be a 1 in a million shot IMO for a coho to display dorsal, adipose and tail spotting in the fashion that the fish pictured does.