Have you ever wondered how fast fish grow? Or, how many years it takes for a certain species of fish to reach “keeper” size? In my previous article, I described the various fish-aging structures and methods that DNR fish biologists use to age different species of fish and how they use that information to make informed fisheries management decisions. This week, I would like to provide some insight into how long it takes for different species of fish to reach a certain length.

Fish grow at different rates depending on which part of the country and what type of lake they are living in. In general, fish in the southern parts of the country grow much faster than fish living in the northern part of the country. The growing season or the length of time that water temperatures are ideal for fish growth are longer the farther south a fish lives. There is even a difference in growth rates between southern and northern Minnesota fish.

In Otter Tail County, fish typically only grow during three months of the year, June, July and August. Once water temperatures begin to decline in September, fish growth stops and excess calories are preserved as fat for the long winter ahead instead of continued growth. In the spring, energy is spent on spawning instead of growth. With such a short window of opportunity for fish to grow, many anglers are surprised to find out how long it takes to produce a “keeper” sized fish.

The type of lake a fish lives in also determines how fast it may grow. Shallow, fertile bodies of water tend to warm quicker in the spring and have more productive food chains. Growth rates tend be faster in these types of lakes. Deep, less fertile lakes take longer to warm in the spring and have less productive food chains, which leads to slower growth rates.

In the remainder of the article, I will outline the average growth rates for some of the more popular gamefish species in the county. Most gamefish species sexually mature at about the same age as anglers consider them “keepers.”

Walleye is the state fish and possibly the most sought after species of fish by anglers in Otter Tail County. Walleyes are typically about 6 inches in length after their first year of growth. On average, a 14- to 15-inch walleye (1 pound) is 4-5 years of age. A 20-inch walleye (3 pounds) is usually 7-8 years of age. Walleyes in excess of 20 years of age have been documented in Otter Tail County.

If there is one species of fish more popular than the walleye, it may be the family of sunfishes or more specifically, the bluegill. In most lakes, bluegills don’t reach a “keeper” size of 7-8 inches until they are 6-8 years of age.

Black crappies are also a popular gamefish species, especially during the ice fishing season. Most anglers consider a 10-inch crappie a “keeper” and on average, a fish that long would be 5-6 years of age.

Although bass are not routinely harvested by anglers, many anglers pursue them for their sport-fighting ability. A 14- to 15-inch bass (2 pounds) is on average 5-6 years of age. A 20-inch bass (5 pounds) is approximately 10 to 12 years of age.

Northern pike are also a sought after sportfish, especially by spearers during the ice fishing season. Northern pike typically reach an average length of 25 inches (4 pounds) at 4-5 years of age. A 34-inch pike (10 pounds) is 8-10 years of age.

Muskies and lake sturgeon are generally not harvestable species, but they can attain old ages and grow to very large sizes. Muskies can reach lengths of 50 inches or more, which typically takes 15-20 years. Lake sturgeon don’t sexually mature until they are 20-25 years of age, and will have attained a length of 50-60 inches or greater at that point.

The next time you catch a “keeper” fish of a certain species, you will now be able to estimate approximately how old it is.

For questions or comments concerning local fisheries resources, contact MNDNR fisheries at 218-671-7930 or e-mail at fergusfalls.fisheries@state.mn.us

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