How to age fish in your pond | Living the Country Life

How to age fish in your pond

Unless you catch a lot of fish out of your pond, you really can't tell how they're doing. Having a biologist age your fish can reveal many factors about pond quality.

Radio interview source: Brian Graeb, Associate Professor of Fisheries, South Dakota State University

It's true - you may have fish in your pond over 25 years old!
Brian Graeb is an associate professor of fisheries at South Dakota State University. He says knowing how old the fish are gives you an idea of the health and quality of the pond's ecosystem. For example, if most of the fish come from just a few age groups, it tells you that reproduction is spotty.  
"So that would indicate maybe you have some sort of spawning habitat or rearing habitat issues," he says. "A lot of times it might be a lack of vegetation, for example. A 15" large mouth bass, it's a big difference if that 15" bass is three-years old and growing really fast, or 12-years old and growing really slow. That tells you a lot about the prey supply in your pond."
Biologists use a variety of techniques to tell how old a fish is. They observe the scales, clip off a fin ray, or look at the otolith (OH'-toe-lith) which is the ear bone inside the fish's head. Graeb says the otolith provides the most precise information. 
"The otolith is a fairly small bone, but it has very distinct growth bands," says Graeb. "We can prepare otoliths in a variety of different ways, put them underneath a dissecting scope, and it's just like counting rings on a tree. We look at the dark and light bands, and that will tell us age structure."
How many fish it takes to make the assessment depends on the body of water.  Hundreds of fish may be analyzed from a large lake. But Graeb says for most farm ponds, a sample of 25-to-30 fish in a range of sizes will do. 
There is no set schedule for often the fish should be aged. Cal a biologist if you haven't done an assessment in awhile, or you just bought an acreage with a pond, or you're worried about the health of the fish. 

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