A stomach pump is an extremely useful tool when trout fishing which can help you quickly identify hatches and trout feeding preferences. With a little practice anglers can quickly obtain a stomach sample without injuring the trout and change flies accordingly.
Why Use a Stomach Pump for Trout?
You step foot in the Watauga River and feel the chill of the 53F water through your waders. Through the mist you can see fish rising, and confidently tie on a dry fly. You make several casts with your confidence falling with each. You've read Caddisflies (Gary LaFontaine), Trout Lessons (Ed Engle), In the Ring of the Rise (Vincent Marinaro), …and many more. You try to read the rise forms and you scan the surroundings for bugs. The only problem is that there are multiple sizes, colors, and species flying around. It seems like they should be taking those big March Browns… or maybe those larger caddis…
Out of desperation you tie on a Sulphur Squirrel Duracell that you got at the fly shop and manage to catch a small rainbow… Savvy anglers know that if they can just catch one, they can crack the code…
Enter the Stomach Pump
Historically anglers approaching a difficult hatch would do their best to catch a single naïve, generally small, trout. After quickly dispatching of it, they would check its stomach contents to get a sense of what bugs were available, and what was on the menu for the more difficult fish.
Times have changed, and now we have plastic stomach pumps. Resembling mini turkey basters, these tools help us pump trout stomachs in order to see what they have been eating. After stealing a trout's last meal you can send it on its way.
The observations garnered from these tools are invaluable. They can help you crack the code on a hatch, and also build (or lose) confidence in your fly selection. I can't tell you how many times I have pumped a stomach and laid my fly down alongside the naturals, only to find that I am one or two sizes too big.
How to Use a Stomach Pump
There are a few simple steps to performing a stomach sample on a trout:
- Squeeze the air out of your stomach pump and fill it full of water
- Hold the fish upside down (usually with your left hand)
- Squeeze out about 25%-33% of the water and leave the bulb compressed
- Insert the stomach pump carefully
- Release pressure on the bulb to suck out the stomach contents
- Quickly release the fish
You can also check out our short YouTube video here:
Why the Water?
Water compresses less than air. By getting most of the air out and replacing it with water you are able to increase the amount of suction that you are employing.
Upside Down Trout
Holding the trout upside down disorients them and makes them less likely to flop around. Obviously it doesn't completely immobilize them, so be careful and take care of the fish.
Squeezing out the Water
It is important that you squeeze the water out, prior to inserting the tube deep into the fish's throat. You want to avoid pumping a bunch of water directly into its stomach. Err on the side of squeezing early rather than late!
Releasing… aka Sucking Out the Stomach Contents
Hopefully as you release pressure on the bulb, it will expand and stomach contents will be pulled into the tube. If nothing happens, slowly pull the tube out of the fish – sometimes this allows things to flow.
If you don't get anything after your efforts, maybe try a second time but definitely don't try a third. I usually try once and let the fish go. If I don't get a good sample, it doesn't mean that the fish's stomach was empty. It also doesn't mean that I don't know what I'm doing. It's just not worth putting the fish through the additional stress and potentially injuring it.
Does a Stomach Pump Hurt Fish?
It can. That's why it's important to land the fish quickly, be careful when attempting to obtain a sample, err on the side of being overly cautious (even if you don't get a good sample), and release the fish quickly. Do not attempt when water temperatures are elevated (above 65F), and never pump an exhausted fish. Limit yourself to two attempts. With practice you can have minimal impact on the fish!
What Size of Trout Can You Pump?
It's difficult to get a good sample from larger fish. If you catch a larger fish, focus on releasing them safely, not getting a sample. Similarly, the stomach pump just doesn't work with smaller fish given the diameter of their throat. I never pump a fish under 7” or over 16”.
I Have a Handful of Half-Digested Bugs…
Great! Make sure you:
- Take a picture for future reference!
- Try to identify what type of bugs you see and at what point in their lifecycles you are finding them
- Set some of your flies down next to them to do a color and size comparison
- Make special note of your hook if you've got the size right!
- Keep watching! Often times some of the bugs will hatch in the palm of your hand. This can be a hard period of the lifecycle in which to make observations so you can get some really amazing insights.
- Switch flies if appropriate… and don't if you have confidence in what you are already throwing
Where Do I Find One?
If you'd like to pick one up, you can find them here:
FAQ
Is it safe to use a stomach pump on trout?
Yes, when done correctly on a healthy fish of appropriate size (roughly 7″–16″) and released quickly afterward. It causes far less harm than a swallowed hook or rough handling.
Does a stomach pump hurt the fish?
There's no evidence of lasting harm when the technique is used carefully, the fish is handled gently, and it's only pumped once.
How much water should I put in the pump?
Fill it completely, then squeeze out about 25–33% before inserting — water compresses less than air, which increases suction.
What if I don't get a sample?
Try once more at most. An empty pump doesn't always mean an empty stomach — but it's not worth stressing the fish further for a third attempt.
What's the best stomach pump for fly fishing?
The Wapsi and Hareline stomach pumps are both solid, affordable options — see the links above.
Good luck, and we hope this helps you bring a few more fish to net and better enjoy your time on the water!