In the last week I have caught two trout in two different streams that had a noticeable bulge directly behind their head or gill slit. When I caught the first fish I thought it had swallowed something big and had yet to digest it completely; although the bulge appeared on both fish to be above the stomach area as I understand it to be.

In both cases the trout in question were brown trout, healthy and wild not bigger than 12" caught from streams. Here is a picture of trout #2.



Does anybody know what may cause this or have you seen it before?