How to Tell the Difference Between Stocked and Wild Trout

An incredibly common question asked within the angler community is how to tell the difference between a stocked and wild trout. For those unfamiliar with the terms, a stocked fish is one that was birthed and raised in captivity (often called a hatchery), alongside hundreds of other fish. These fish are bred in the interest of providing anglers with the opportunity to catch trout in waters which, due to a myriad of different reasons, could not support a healthy trout population naturally. On the other hand, wild fish are trout that are born in the stream without any human intervention. Note, the term wild and native are often misused when identifying said fish. Wild fish are as described prior, whereas native fish are a naturally occurring species in the water system. For instance, the great state of Pennsylvania has hundreds of healthy wild brown trout streams, however, brown trout originally hail from Europe. Brook trout, on the other hand, are a native species to Pennsylvania streams.

When looking to identify a wild fish vs. a stocked fish, there are a plethora of different methods one can employ, some more effective than others under certain circumstances. Below are some of the best methods to see how to tell the difference between stocked and wild trout.

NOTE: For many of these identification factors, things change with time. Stocked trout usually don’t survive for more than a year (if that) when introduced into heavily fished streams. However, the ones that do usually begin to closely resemble their wild counterparts in looks and mannerisms.

1. Color

stocked v wild brook trout
Image courtesy of Phys.org

When trying to tell the difference between a “stocky” and a wild fish, the coloring is one of the biggest giveaways. While this has been changing in certain areas over the past few years, stocked trout are primarily fed on a pellet based diet. Whereas wild fish possess the ability to consume a largely diverse amount of food, stocked fish lack the intake of certain minerals and proteins often found in insect larvae and freshwater shrimp that affect the pigmentation of the fish. Another reason for this is due to the fact that stocked fish are raised in protected environments. Their survival does not hinge upon a specific color gradient, therefore natural selection doesn’t play a role in their development.

2. Damaged Fins or Skin

clipped fin trout
Image courtesy of Nebraskaland magazine

Considering these fish are often raised in confined spaces amongst hundreds of other fish, it’s more common than not to see fish with shredded fins and tails, or large scrapes all over their bodies. These features are abundant of freshly stocked trout, and result from a life spent scraping up against cement walls and being nipped by other fish. While over time fins and skin grows back, some injuries are good enough where they will forever be identifiable. There are also circumstances where fins will be intentionally “clipped” for identification purposes. If you see a fish with a dorsal or adipose fin that looks like it was clipped with scissors or some sharp object, there’s a good chance it’s a stocky.

3. Fat Content

fat rainbow
Image courtesy of Wmdfly

Because of their diet, as well as their living conditions, stocked trout usually possess an abnormally disproportionate distribution of fat. Because stocked trout are raised in holding ponds and fed by humans, they do not have to expend energy swimming up current or searching for food such as a wild trout would. Likewise, instead of a balanced diet of bugs and other fish, these fish are fed high-fat pellets (with the end goal obviously being to get them to grow as large as possible in the shortest period of time). When you see what looks to be a juvenile trout with an abnormally large amount of fat around its stomach (commonly referred to as footballs, or pellet pigs), there is a decent chance it’s a stocked fish.

4. Eating Habits

rainbow trout eating
Image courtesy of Georgia Outdoor News

As mentioned above, the diets of stocked trout vs. wild trout differ massively. While stocked fish quickly learn to begin to look for food for themselves a few weeks after introduction into a stream, they have been raised to be accustomed to being fed feed pellets. Because of this, their feeding behavior (within a few weeks of stocking) will be largely different from trout that grew up hunting for food. Often times stocked trout will not eat flies or other tackle besides power bait, eggs, and corn after being introduced into new water. However, after a few weeks, their eating habits begin to make a complete 180. After these fish learn that they must obtain food for themselves, they’re oftentimes much easier to catch than wild trout. Due to their lack of knowledge of what should and shouldn’t exist in the stream, these hungry fish will oftentimes strike at anything that drifts by their heads. So, the next time you see the stocking truck roll by your favorite stream, give the fish a week’s time.

5. Location and Local Regulations

stocked sign
Image courtesy of Simpson Fly Fishing

In most states, stocked trout water will be marked by that state’s fish and game commission. Most of the time these notices will be stapled to trees or pasted to signs that border the water where you’ll be fishing. So, if you catch a fish that has any semblance of what has been described above, but you still can’t figure out whether it’s stocked or wild, just take a look around and see if you can spot any of these signs. If you find one, there’s a good chance you’ve got yourself a stocked trout. Note that just because a river is stocked, doesn’t mean there are no wild fish. If the water seems clean enough to hold wild fish, there’s a strong possibility the river holds a mix of stocked and wild fish. Whether or not stocking these wild streams is helpful or harmful is a whole other debate. By using the identifying features mentioned above, you shouldn’t have much trouble figuring out how to tell the difference between stocked and wild trout.

Conclusion:

stocked trout
image courtesy of Wmdfly

Wild or stocked, trout are trout. In understanding the debate pertaining to whether or not there is a place for stocked fish in wild waters, one must consider the effects the introduction of non-native species can have on native fish populations. While it’s always fun to have a wider variety of fish in our streams, it’s important to remember that we are only sharing the water with the rest of its inhabitants, and that we must remain respectful to the delicate balance of an ecosystem. However, there are also people who have grown up fishing strictly stocked streams, as their normal water conditions couldn’t support a healthy wild population. Without these stocked fish, many people would not be able to fall in love with the art of catching a trout on the fly, and subsequently aiding in the growth of the fly fishing community. In the sport of fly fishing, as well as all other elements of life, balance and respect are two key components that one must value.

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