Fly Fishing for Triploid Brown Trout

What is a Triploid Trout (Why are they so Big!)

Managing trout populations is something many anglers care about, but we often don’t fully understand how it’s done. Trout are sensitive fish, so keeping their populations at healthy levels isn’t an easy task. One of the more common ways game and fish departments manage trout populations is through trout called “triploid trout.”

Triploid trout are fish that are sterile. They’re nearly identical to other trout in all other ways, but they are unable to reproduce. As a result, most of their time is spent feeding. They’re able to grow to impressive sizes and become primary targets for anglers looking to keep trout populations healthy.

How to Fly Fish for Brown Trout
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What Exactly Are Triploid Trout?

As mentioned earlier, triploid trout are sterile. However, they’re not true genetically-modified fish. Genetically modified fish have their genetic material changed by inputting desired traits from other organisms. Triploids haven’t had their DNA modified. However, they had a third set of chromosomes added to their DNA to make them infertile.

“Normal” trout (diploids) only have two sets of chromosomes that allow them to fully reproduce and act traditionally. Male triploid trout, however, often act in traditional ways during the spawning season.

Male triploids will spend time near Redds and even interact with spawning females, but they aren’t able to complete the reproduction process. Female trout will quickly ignore these triploid trout when they determine that they’re unable to fertilize their eggs.

Female triploid trout do not show any sort of spawning behaviors when the right time of year arrives. They spend most of their time focusing on feeding rather than reproducing.

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How Are Triploid Trout Created?

The science behind creating triploid trout isn’t overly complicated. The whole goal is to move away from the traditional XX (female) and XY (male) chromosomes and create XXX (female triploid) and XXY (male triploid) trout. There are two ways that they are most often created: heat shock and pressure treatment.

Scientists will begin by applying the third chromosome to the egg and fertilizing it. They’ll wait and give it time to produce what is called a “polar body” that allows the chromosome to attach and become a part of the egg. Once this occurs, scientists will “heat shock” the eggs to force that third chromosome to stay on the egg.

Pressure treatment is similar to heat shocking, but instead of high heat, scientists will put the eggs under high pressure to keep that third chromosome attached.

Rainbow Trout Scales
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Why Do Triploid Trout Exist?

One of the primary goals with triploid trout is to introduce them to a body of water and have them not harm native fish. If there is a native or wild population of rainbow trout in a lake, game and fish departments will release a decent number of triploid trout in these waters, so anglers will not only catch all native fish. It helps keep the population in a good place.

Another reason triploid trout exist is to keep the DNA of those genetic or wild populations as pure as possible. The triploids allow the native populations to reproduce and exist, but still keep the numbers high. While game and fish departments could stock hatchery-raised fish, it can ruin the purity of the wild or native fish.

Their DNA can almost ruin the current genetic system that’s in the wild or native fish, and that’s the last thing game and fish employees want. Triploid trout won’t mate with the native fish, but still keep populations high and give anglers something else to target.

One of the final reasons why triploid trout exist is to eradicate a body of water of unwanted non-native species. Triploid trout focus all of their energy on feeding, so they’re extremely aggressive and willing to eat regularly.

Triploids will be introduced into the lake, and start eating some of the unwanted fish and scientists don’t have to worry about triploids mating and messing up the genetic pool. It’s a win-win for all involved.

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Are Triploid Trout Bigger than Diploid Trout?

Some anglers would swear that triploid trout are larger than diploid trout because all of their attention is focused on feeding. However, there is no significant data that proves that triploid trout are bigger than diploid trout.

Even though diploid trout have to go through the exhausting process of spawning and reproducing, they’re still able to feed and grow to the same size as the majority of triploid trout. The numbers and sizes of fish may vary depending on where you’re targeting them, but for the most part, the fish grow to almost equal sizes.

Is it Legal to Catch Triploid Trout?

Yes, it is fully legal to catch triploid trout. Game and fish employees as well as anglers almost prefer to catch triploids because they know the catching of these fish won’t impact the wild or native trout populations. Many states will still have limits on the number of triploids anglers can catch, but there’s nowhere in the United States where it’s illegal to target or land them.

These fish were essentially created to give anglers a chance to catch trout and not have to worry about harming any of the more essential fish populations.

Are There All types of Triploid Trout?

Yes, there are all different types of triploid trout. Wherever game and fish employees feel the need to protect a population of trout, they’ll often introduce triploids. Rainbow and brown trout are generally the most common types of triploid trout that are introduced.

Last Cast

Triploid trout are a great example of what it takes to keep fish populations healthy. With the growing number of anglers that are continually entering the sport, efforts need to be made to protect our natural resources. Triploid trout still give anglers the joy of landing fish, but not with all of the concern over what a fish undergoes when they’re caught.

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Danny Mooers is a high school English teacher in Arizona with a love for fly fishing. Growing up in Minnesota gave him the opportunity to experience all types of fishing and grow his skills. After living out in the Western United States for several summers in college, his fly fishing obsession grew. Having the opportunity to share in his passion for fishing through writing is a dream come true. It’s a lifelong hobby and he strives to make it understandable for people of all skill levels


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