My Science Box

Salmon alevins: Just hatched salmon with yolk sacs. Image courtesy of U.S. Fish and Wildlife Service.Teacher Background
Raising trout provide a fabulous way to introduce students to the life cycle and physiological requirements of other species. Moreover, you can use these fish to teach students about threatened and endangered species.

Oncorhynchus mykiss (rainbow trout or steelhead trout) are the most commonly encountered species in classrooms. They are native to the West coast of North America but have been introduced to oceans, lakes and rivers world wide. They are a highly prized game fish in many North American rivers.

They belong to a class of fish known as salmonids that includes salmon and trout. Salmonids are anadromous, that is, they are born in fresh water but may spend much of their adult lives in the ocean, returning to the rivers in which they were born to spawn and lay their eggs. The freshwater form of Oncorhynchus mykiss is called rainbow trout. These fish may spend their entire lives in fresh water. The saltwater form is known as steelhead trout. These are generally larger than rainbow trout and can find their way back to the stream of their birth to spawn and lay eggs. Steelhead are then able to migrate back to the ocean and repeat the cycle several times in their life. Salmon, the other genus of salmonids, die after spawning and do not return to the ocean. For more information on the trout life cycle, see the Nevada Trout in the Classroom website.

Rainbow trout: Image courtesy of US. Fish and Wildlife ServiceIn order for young trout to survive to adulthood, several conditions must be met:

1. They need high quality water. There must be high levels of dissolved oxygen (6-9 ppm), cold water (ideally 45-55°C), high winter flows and continuous summer flows.
2. They need loose, pea-sized gravel for females to form nests and lay their eggs.
3. They need cover for hiding from predators. Undercut banks, rocks, gravel and wood debris are ideal.
4. They need a plentiful food supply. The hatchlings are known as alevins and will feed on their yolk sac until it is gone. Thereafter, they are known as fry and will eat plankton and aquatic invertebrates such as mayflies, caddisflies, damselflies, and other insects. When they reach maturity they smolt (change their physiology in order to survive in salt water), migrate to the ocean, and eat shrimp and small fish.

Each of these factors (besides the food supply since the alevin will have a yolk sac while in the classroom) must be carefully recreated in the classroom aquarium. Steelhead are classified as a threatened species since water diversion (dams), migration barriers (culverts, roads, and walls), habitat destruction, introduced species and creek disturbances (pollution, trash, dogs, erosion, etc.) have dramatically reduced the amount of acceptable habitat.

Different parts of the country have different programs for teachers to raise salmonids in their classrooms, each with its own set of rules and regulations. See the Procedures below to get in contact with a program near you. Information on how to set up a tank and care for your fish can be downloaded from Trout Unlimited. Curriculum resources may be downloaded from the Nevada Department of Wildlife.

Student Prerequisites
None