See my previous discussion of Brook Trout spawning behavior.
I’ve seen aggression near the spawning redd before, but never have I seen a male so aggressive as to clamp his entire jaws around the body of a rival of the same size. This behavior was repeated over and over, and these fish were both looking exhausted. The one larger male was chomping on fins, the entire body from tail to head, and even went for the eyes once. Hyper aggressive. If you’v caught these trout, you know they have small but sharp teeth.
I was shooting the Olympus E-M1 with the Panasonic/Leica 25mm f/1.4—fast focusing, but was really tough to get a photo—I crawled up on my belly (trout spook very easily) and took many shots. But the fish are so fast and change direction so frequently that at 1/125 and the limited depth of field made it tough. Still, you can get the idea here:
See also Brook Trout Spawning.