- Trout lay their eggs in nests in the river gravels, known as redds.
- The female builds the nest, when the water is cold and carrying lots of oxygen, because that is what the eggs need to hatch.
- She will then release some of her eggs.
- The male fish will release his sperm or milt over the eggs to fertilize them. The hen then moves forward and digs again to throw up gravel to cover the fertilized eggs.
- Redds can vary enormously in size, from 50 cm2 to over 150 cm2 how many eggs are laid also depends on the size of the hen trout, a 500 g trout will typically deposit around 800 eggs.
- As the eggs develop, you can see trout ova develop within them. This is called the eyed ova stage.
- How quickly the eggs will hatch depends on water temperature. Colder water means slower development in the egg.
- The egg takes about 97 days to hatch. Most of the eggs hatch in February.
- They are called alevin.
- Once the yolk has been eaten, the alevin become fry.
- Then they light and start to feed on tiny insects in the water. Mortality rates at this highly vulnerable stage are very high.
- They also become territorial.
- And they are still very tiny, so they need shallow water 1-40 cm that isn’t too fast flowing.
- A trout of less than one year old is called a parr. You can recognize them as trout but they have distinctive fingerprints or parr marks along the side which they lose as they get older.
- Parr have similar habitat needs to fry. Plenty of cover to hide from each other and from predators, especially fish eating birds.
- They can cope with deeper and faster water as they grow.
- In order to find their own territory, they will gradually drop downstream with the flow rather than fight their way up against the flow.
Migration/ Light Conditions
- Brown Trout naturally want to ascend into rivers from the sea to spawn.
- Since most rivers are landlocked here in the US the fish still cannot fight the instinct to move to the upper sections of rivers to spawn.
- Shortening days and decreasing water temperature affect hormone concentration.
- Light conditions have a very important role in the reproductive behavior and activity of trout. Shortening days stimulate development of eggs and activate the instinct to proceed with the spawning.
- Brown trout spawn when the water temperatures range between the mid forties and high forties.
- Of course, this water temperature must exist at the right time of the year which in the southeast is from the middle of October to the middle of December.
- The peak of the spawn is usually around mid November but that is subject to weather and water conditions. The brown trout spawn will usually follow the brook trout’s spawn.
- Prior to spawning, both genders increase their intake of food.
- One is to provide the energy needed for the migration to their upstream spawning areas and
- The other has to do with the hen producing the eggs
Depth of Watter
- It's normally from about 6 inches to 16 inches in depth.
- Extreme high and low water levels can affect the spawn and the survival of the eggs, and as well as the survival of the hatching trout.
- The effect of current can not be over emphasized as it has a great effect on the success of the spawn.
- They prefer cool, clear rivers, streams, and lakes, though some will leave their freshwater homes and follow a river out to the sea. These migratory adults, called steelheads because they acquire more silvery markings.
- They will spend several years in the ocean, but must return to the stream of their birth to spawn.
- Rainbow trout spawn in the spring.
- Brook and brown trout are fall spawners.
- Brook trout generally spawn between September and November and brown trout spawn a little later, usually between October and December.
- Brown Trout are anadromous Which means they naturally want to ascend into rivers from the sea to spawn. Since most rivers are landlocked here in the US the fish still cannot fight the instinct to move to the upper sections of rivers to spawn.
- They are native to the alluvial or freestone streams that are typical tributaries of the Pacific basin, Great Basin and Rocky Mountains.
- Cutthroat trout spawn in the spring and may inadvertently but naturally hybridize with rainbow trout, producing fertile cutbows.
- So they spawn in the same time as rainbow trout, the spring.
- Bull trout usually mature between 4-7 years of age.
- An individual may spawn annually or every other year.
- Bull trout typically spawn from August through November during periods of decreasing water temperatures.
- Spawning habitat consists of low-gradient stream reaches with loose, clean gravel.
- Lake trout spawn in autumn at extreme depths (often more than 100') - otherwise, they will spawn in the deepest, coldest part of a shallower inland lake.
- The female will clear out a patch of gravel with her tail, then scatter her eggs for a male to fertilize.
- So lake trout spawn at night during the autumn months.
- A hybrid is created when a different spices of trout that live in the same habitat and spawn at the same time of year.
- For example a cutthroat trout and rainbow trout spawn in the spring so they create a cutbow.
- Another example is a brown trout and a brook trout. They both spawn in the fall so they create a species called a tiger trout.