Stomach pumps are the most direct way to determine what trout are actually eating.

The process is simple and easy and if you follow these directions, and it will not harm the fish.

1. Fill the bulb full of water
2. Cradle the trout gently upside down
3. Slide the tube into the trout's mouth and squeeze out the water before sliding it down the fish's throat.
4. Keep the bulb depressed while you gently slide the pump into the fish's throat. Stop when you feel resistance.
5. Let go of the bulb and slide the pump back out. The contents (trout's lunch) will come with it.