How the Trout Spawn Works

By: Rosalind Jackson

School of Rainbow trout (Oncorhynchus mykiss) swimming in pond, Mpumalanga, South Africa
School of Rainbow trout (Oncorhynchus mykiss) swimming in pond, Mpumalanga, South Africa
Max Paddler/Gallo Images/Getty Images

Your seventh grade science class is­ falling asleep at the wheel, so to speak. You try a different method of teaching your kids about animal reproduction from the textbook daily. You are at your wits' end; nothing seems to bring their heads up from their desks. A fellow teacher listens to your complaints and suggests a good, old fashioned field trip. Why not bring your class to the local river to watch the trout spawn?

Trout spawning is a very exciting moment in the lifecycle of the trout, and it's sure to breed some interest among your students. If they've never been to a river to watch fish, or even if they've gone with their family on yearly fishing trips, the tro­ut spawn is a perfect example of reproductive processes found in the natural world.


­Trout develop from egg to fry in the rivers, tributaries or sandbars where they were deposited by their parents. As fry, the developing trout must learn to survive without the protection of shelter and must rely on themselves for food. From the fry stage, which generally lasts about a year, trout develop into parr. As parr, the trout remain in fresh water and accrue parr bars, which are vertical grown marks that appear on both sides of the trout. As the parr develop into smolt, they leave streams and rivers they were born in to mature in more rugged water and to prepare for spawning [source:].

Read on to learn more about when trout spawn.


When Trout Spawn

Once the smolt matures into an adult, it will spend a few years eating and growi­ng in order to get ready for spawning. Some species of trout migrate from streams to very large bodies of water, like lakes and even oceans, while others merely head upstream. Adult trout that have moved to larger bodies of water have access to much more food, and it's during this stage in the life cycle that most of their growth occurs.

As adult trout near spawning maturity, they begin to undergo changes in their color, behavior and anatomy. The trout's exterior shifts from a silvery color to bright red, pink and green. The closer to the spawning event, the easier it is to distinguish between the male and female trout. Male trout develop a hooked jaw called a kype, which elongates in size. The female, as the eggs grow in the abdomen, becomes more rounded and stout.


Different species of trout spawn during different times of the year. Depending on what trout species inhabit the areas near where you live, and what trout species you're interested in observing, you'll want to make sure that you coordinate your visit with the correct spawning season.

Rainbow trout spawn earlier in their lives than most other trout species (at roughly two years) and their spawning season occurs in the late spring and early summer as water temperatures rise. Brown trout spawn in the fall, from late September to early November, and are primarily active during the daytime. Lake trout, on the other hand, spawn at night during the autumn months.

You've got the time nailed down, but where's the best place to invade these spawning trout's privacy? Read on to find out.


Where Trout Spawn

Just as many trout species spawn at different times of the year, many trout species spawn in different locations. Lake trout, for instance, don't leave the lake to spawn, but instead search for an appropriate area within the lake to perform spawning, usually a sand bar or graveled shore. Anadromous trout species, li­ke rainbow trout and the brown trout, return to the streams and tributaries in which they were born to spawn. Some smaller trout species remain in rivers they developed in, only to return upstream for spawning activities.

As spawning begins, the female trout will scout out a shallow, oxygen-rich lake or river bed to deposit its eggs into. The female will then carve out a small trench called a redd by scooping out the gravel and sand with its tail. Once the redd is complete, the female will deposit her eggs and wait for a male to fertilize them with his sperm. Males will often fight with each other using their recently developed kypes to battle for the best territory on the spawning grounds. Upon completion of spawning, the female will cover the red with loose gravel and sand as it swims away, providing the future hatchlings with shelter. Unlike salmon, trout don't die after spawning and can participate in spawning multiple times in the course of their life [source: USDA Forest Service].


During a spawning season, a single female rainbow trout can spawn 200 to 8,000 eggs. Of the eggs that are fertilized, very few will survive to become mature adults, having fallen prey to predators such as large insects, amphibians, water pollution and hungry fish, even including mature trout.

Swim over to next page to read about how an angler can fish for trout during the spawning season.

Trout Fishing During the Spawn

Aside from watching the exciting ac­tivity of the trout in waters during spawning season, some people may want to utilize the large quantity of trout in the water by fishing. Fishing during spawning season is very effective because there are so many fish in the water and the fish need more food to maintain their energy level for the spawn.

There are many different methods of fishing that are useful during spawning season. Perhaps the most productive technique during spawning season is fishing with fish eggs. Trout and salmon eggs are used as bait on the end of a fishing line to mimic a natural grouping of fish eggs. The trout are so enticed by fish eggs during spawning season that they'll often ignore all other types of baits and lures and bite exclusively at egg sacks. Egg sacks are composed of cured trout or salmon eggs and are bundled together with netting in groups of 10 to 15 eggs [source: Lake Michigan Angler].


Fly fishing is another popular method of fishing used during spawning season. This method is practiced in rivers and employs an artificial lure to get the fish to bite. The artificial lure in fly fishing resembles an insect or other prey, often a fly, which is where the method gets its name.

During the spawn, the most efficient fishing practices are performed from the shore or in the river or lake itself. You will probably want to stray from using a large boat, especially one with a motor. Additionally, you will want to be on the lookout for some of the trout's other predators during the spawning season, which include low-flying bird of prey, other large fish and water-dwelling animals like the otter.

Now that you've got the know-how, you can visit some spawning trout for an educational lesson -- or just some good fishing.­

Lots More Information

Rela­ted­ HowStuffWorks Articles

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