Body size and color are often the least accurate in determining species. The main reason to rule out pink is scale size as pinks have very tiny scales compared to the rest of the salmon. While I admit the spotting pattern is more typical of Chinook, I have caught coho with similar spotting pattern as this fish. Three characteristics that sway me away from Chinook are the white gum line, lack of profuse spotting and silver pigmentation in the tail, and the anal fin is much smaller than a Chinook. Based on these reasons I vote for coho.