Lesson Plans - Aquaculture
There are many different kinds of farms in the world. There are vegetable farms that grow beans, potatoes, and corn, orchard farms that grow apples, oranges, and pears, and animal farms that raise cows, pigs, horses, and sheep. But there's one kind of farm that's very unusual, because instead of fields for vegetables, or pens for animals, the farmers raise their crops in acres and acres of water. And instead of cows and pigs, these farmers raise fish. You may have thought that all fish swim freely in the oceans, rivers, and lakes. But since ancient times, people have raised many different kinds of saltwater and freshwater fish and plants as food. This type of farming is called Aquaculture.
Why do people raise fish on farms? For the same reasons they grow vegetables or raise cows and other farm animals: to feed hungry people, and make sure there is enough food all year 'round. If you've ever gone fishing you probably know that there are some times when you don't catch any fish at all, and other times when you can catch a bunch in one afternoon. When fish are raised at a fish farm there are always plenty of adult fish ready to "harvest" all the time. At a fish farm you can also control the temperature and condition of the water and control the food that the fish eat, so that the fish are always healthy and strong. Healthy fish taste best and are very nutritious to eat.
In the United States several types of aquatic animals are raised on farms. Some are saltwater fish and shellfish that live in the ocean like shrimp, clams and oysters. Others are freshwater fish that live in rivers and lakes like Rainbow Trout and catfish. Salmon and some kinds of trout live part of their lives in the ocean and part of their lives in rivers and streams. Their bodies can adapt to both salt and fresh water.
Let's learn how Rainbow Trout are raised on a fish farm in southern Idaho. Here, in a special place called the Magic Valley, a hidden underground reservoir of clean mountain water gushes right out of the walls of the Snake River canyon. Because the water spends most of its time underground, it's constantly filtered through volcanic rock, so when it flows out of the underground lake it's very pure and clean. Whether it's summer, winter, spring, or fall, the water always stays at 58ยบ Fahrenheit, the ideal temperature for raising trout. That's the reason why over 75% of the Rainbow Trout grown in the United States come from this one valley in southern Idaho.
Rainbow Trout begin their lives as eggs. The eggs are placed in upwelling incubators in indoor hatcheries. Here oxygen-rich water bubbles up around them. After 25 days, tiny eyes can be seen in the eggs. About ten days later they hatch into tiny fish called fry with a yoke sack still attached to their tails and are moved to indoor ponds. They get all the nutrition they need from their yoke sack. The expression "small fry" probably came from the name of these newly hatched fish. When the yoke sack is all gone and the fry are strong enough to swim up to the surface of the water on their own, they're called "swim-up fry." The swim-up fry are fed special food until they grow to about three inches long. At this stage they are about as long as a person's finger, and they're known as "fingerlings." Now they are old enough to be moved to outdoor raceways where they are carefully nurtured and fed for about eight months.
What do farm-raised Rainbow Trout need to be healthy? Food: specially made fish food that is high in protein, nutritious fish oil, vitamins, and minerals. The water they swim in is also very important to their health and growth. It has to be very clean and pure, it has to be the right temperature, and it has to be full of oxygen. Just like humans, fish need oxygen to live, but they don't have lungs for breathing air, as we do. They take oxygen out of the water, by filtering it through the gills in the sides of their heads. To make sure there is plenty of oxygen in the Rainbow Trout's water, the water flows quickly through the raceways, adding tiny bubbles of air to it. This makes it easier for the fish to take the oxygen out of the water as it passes through their gills. With just the right amount of nutritious food and lots of clean aerated water, the trout grow bigger and stronger.
As they grow they are graded and sorted by size. Groups of fish of the same size are kept together, sort of like different age groups in this school. (That's because if you let the extra-big fish swim in the same tank as the extra-small fish, the big fish would eat the little fish.) When they weigh 12 to 16 ounces they are fully grown and ready to go to market.
How can you tell a Rainbow Trout from a brown trout or any other type of trout? Rainbow Trout have a rosy pink coloring along the side and gill covering. Sometimes they can also have a blue or gold coloring. With all these shimmering colors their skin can look like a rainbow, and that's why they're called "Rainbow Trout." Actually, Rainbow Trout are like chameleons and can become darker or lighter depending on the color of the rocks and sand in the stream where they are swimming.
Rainbow Trout will take on the color and taste of the water they're in. That's why it's important to have a pure spring water source. You may have eaten farm-raised Rainbow Trout before, right here in the school cafeteria. Kids love trout because it has a mild taste and is very tender and flaky. Rainbow Trout is also very nutritious. It's a great source of protein, which is a very important food group that people should eat every day. It's low in calories and fat, and full of important vitamins and minerals.
The scientists who study Rainbow Trout are always working to find better ways to grow strong, healthy fish so we all can enjoy them for lunch and dinner. They study the water they swim in, the food they eat and the way they are handled. The scientists use computers, microscopes, and other testing instruments to make sure all the Rainbow Trout you see at the school, or eat in restaurants or in the school cafeteria are fresh and good for you. Because they're raised on a farm, you can be sure the Rainbow Trout you eat has been raised in pure fresh water and treated with the best care. That's why it always tastes so good.