If I've learned one thing from Brown Trout....

It's always eat the head first.

Apparently, it has something to do with the spiny dorsal fin of the potential meal. If the brown trout eats a fish with a spiny dorsal tail first, it would most likely get stuck in the brown trout's gullet. That may be the logical explanation, I like to think it's because they are mean, ruthless predators. Whatever.