Ladyfisher
Outdoor Writers Association of America
Northwest Outdoor Writers Association
This Week's View

by Deanna Lee Birkholm

The Ladyfisher

September 7th, 1998

What About Stomach Pumps?"


I am not an entomologist. JC has quite a little experience in that field, but not a degreed entomologist either ('tho I must say his knowledge on bugs sometimes is absolutely amazing).

So I must say I am not 'comfortable' using a sampling tool - as a stomach or esophagus sampling pump to find out what the trout is eating.

One of the problems is you have to catch a fish to sample it. And if I have caught one fish, I'd probably be inclined to keep fishing whatever it was that caught that fish. Personal bias of course. But then, I tend to be more of a "free spirit" rather than a "scientific" type.

I personally don't like the idea of sticking a tube down a trout's throat. It seems to be unsporting. Not at all how I was raised to be a fly fisher.

Fly-Rite Pump

That said, I do realize that fly fishers do want to find out exactly what a trout has just been eating. Providing of course the angler can actually recognize the differences in insects. The catch is improper use of a sampling device can severely injure or kill a fish.

So if you are going to use the stomach pump, here is the correct method. We thank Frank Amato Publications and Brian Chan, for permission to reprint segments and photos from the Fall 1998 issue of Fly Tying, "What are the Trout Really Eating? By Brian Chan.

We called Brian Chan, and asked about the article. Brian is the Senior Fisheries Biologist for British Columbia, and well versed in the use of what he would prefer to call a "throat pump." (He personally only uses one in the spring when the fish are eating tiny stuff that may be otherwise impossible to discern.) His original reason for writing the "What Are the Trout Really Eating?" article was to correct the improper 'instructions' included with the Stomach Pump marketed by Fly Rite. Instructions which he feels can severely injure or kill the fish.

The whole process has to be done right, beginning with the handling of the fish once it is caught. This is really is serious stuff.

Basic Fish Handling

"There are some basic rules about handling and selecting fish for stomach analysis. Consider sampling only fish that are at least 12 inches in length. The esophagus of smaller fish may not be large enough to pass the sampling tube without causing damage. How one handles a fish for sampling will largely determine the survival of the fish. Keep the fish in the water. If you use a net, choose one with a bag made of small-diameter, soft, knotless cotton or soft fine-mesh nylon netting. These materials reduce the amount of scale loss and damage to the protective layer of slime on the fish. When handling a fish, cradle it from the underside behind the pectoral fins by making a "V" between your thumb and the other four fingers of your hand. Don't squeeze the fish in the "V" grip, as too much pressure can damage internal organs. Turning them on their side or upside down can calm larger fish. After sampling, revive the fish by moving it back and forth in the current so that well- oxygenated water passes over the gills. Don't release a fish until it easily swims away under its own power.

The Sampling Process

Sampling the very last food a trout has ingested means extracting items from the esophagus or gullet area of the digestive system. The esophagus begins at the back of the throat. It is a short muscular section that expands to take in larger food items. Once the food item passes through the esophagus it enters the stomach where digestive enzymes quickly break down and discolor food items.

Step 3 Lubricated sampling pump with pump depressed, ready to slide into the esophagus.


Stomach or esophagus sampling pumps look like miniature turkey basters. The end of the sampling tube is tapered so that it will pass easily into the esophagus. A soft rubber bulb is attached to a thin diameter plastic tube, which is inserted into the mouth of the fish, and down to the esophagus or stomach. Fly-Rite Inc. manufactures a stomach pump that has a 3/16-inch inside diameter sampling tube. The tube is smoothly finished so that it slips easily into the esophagus.

Step 4 Sampling pump positioned in the esophageal area. Note the depressed bulb as a result of vacuum seal.


Improper use of a sampling pump can damage or even kill a fish. A common mistake is to fill the bulb with water and then squeeze the bulb once the tube is in the esophagus or stomach. The jet of water that is shot into the stomach can rupture the digestive tract. Pushing the sampling pump deep into the stomach also tends to sample food items that have already been affected by digestive enzymes and thus will not give you the most accurate feeding pattern information.

Step 6 Pump is removed and food items flushed into the pump bulb.


Small glass sample vials are excellent viewing platforms to observe "fresh" invertebrate samples while on the water. For instance, you can readily watch midge pupae and mayfly nymphs, that just seconds ago were eaten by a trout, complete the emergence into the adult stage. You will also see how other immature insect larvae and nymphs move as well as make notes on body colours and size of body parts.

Step 7


Revival of fish prior to release.


Properly used sampling pumps are another tool to better determine feeding patterns of trout and improve angling success. Record this information for planning future fishing trips to that particular water and then spend some time at the tying bench to further refine your patterns."

Below are the step-by-step instructions as shown in the Fly Tying article. To the right are the instructions that accompany the Sampling Pump from Fly-Rite.


Fly-Rite Instructions
"Using a Sampling Pump"

1. Flush and lubricate the pump by squeezing water in and out of the bulb and tube.


2. Squeeze excess water out of the tube before inserting into the mouth of the fish.


3. Depress the bulb about half way before inserting into the fish.


4. With the bulb depressed slowly, slide the sampling tube down into the esophagus. You will feel resistance on the tube as it enters the muscle-lined esophagus.


5. Once into the esophagus area, release the bulb and it will remain depressed as a vacuum seal has been formed.


6. Slowly remove the pump and, as the seal with the esophagus is broken, air will such in the last food items that the fish has eaten.


7. Revive and release the fish.


8. Depress the sampling bulb and fill with some water then flush the contents into a petri dish or sampling vial for closer observation." ~ Brian Chan


If you choose this method to find out what the fish are eating you do have a responsibility to do it in the most careful, considerate manner. Not something to be taken lightly.

~Deanna Birkholm

Archive of Ladyfisher Articles

[ HOME ]

[ Search ] [ Contact FAOL ] [ Media Kit ]

FlyAnglersOnline.com © Notice