Fish eggs in gravel
Spawning is the name for trout reproduction. The process of female trout laying eggs and male trout fertilizing the eggs is spawning. Many factors influence the place where a trout may spawn. They include:
- Stream bottom (usually gravel)
- Water depth (between 6-24 inches)
- Water velocity
- Stream cover (trees, bushes, logs, etc.)
The female builds a pit called a redd. She does this by digging with her body. When she is finished building the redd, she then lays her eggs and the male fertilizes them. The female travels upstream and begins to dig another pit. She does this so that the gravel from the new pit will be carried downstream and thus cover the eggs she laid in the redd. Cutthroat trout spawn from mid May to mid July in Montana. If water temperatures are too cold, trout will spawn later when the water warms up.
After the eggs are fertilized they begin developing. The first stage of development is the eye. A yolk sac, that provides nutrients to the small fish, then develops. These small fish are called "sac fry". When the yolk sac is absorbed the small fish make their way out of the riverbed gravel. The incubation time is 2.5 months. The warmer the water the faster the eggs will develop. It is very important that water flows through the gravel to allow oxygen to make its way to the eggs and carry away the wastes. Sediment can interfere with this process. Some of the natural causes of sediment are earthquakes, mudslides, and fires. Man-made causes can be overgrazing, poorly designed roads and digging near stream beds.