When do trout spawn? (and the factors that determine it)

Want to know when trout spawn, and the conditions that trigger it? Will on this page, I have listed the spawning times and conditions for major species of trout. I also need to note, that these dates are for the northern hemisphere only. The months are opposite for the southern hemipshere.

As an added bonus, I also included a section discussing when do trout spawn at the equator?

The months when different species of trout spawn (northern hemisphere)

Temperature range that trout spawn at.

Rainbow troutHigher than 41f
Cutthroat troutHigher than 42f
Brown troutLess than 53f
Brook troutPossible at 60f but ideally less than 53f
Bull troutLess than 48f
Lake troutLess than 50f

When do Rainbow trout spawn?

Rainbow trout potentially spawn across long periods of time, mostly depending on elevation, the spawn can begin as early as the first week of March and it continues throughout the spring into early summer. At high elevations, the latest spawners are usually done by the end of June with a few strugglers still spawning as late as July.

While many factors such as changes in water temperature, and increasing day length help determine the start of the spawn. Many rainbow trout, at least in mountainous areas with snowpack start their spawn to coincide with the melting of the spring snow.

If the water temperature does not raise above 40f, rainbow trout do not begin to spawn even when accompanied by an increase in flow which is another condition that can trigger the start of spawning.

The young rainbow trout fry typically hatches early in the fall and can be found living in the gravel from April onwards.

When do cutthroat trout spawn?

Cutthroat trout spawn around the same time as rainbows, but they tend to start and end spawning about a month later. At lower elevations, cutthroat can begin spawning in early April, and the spawn continues through to late July.

Wikipedia claims cutthroat trout spawn in water temperatures between 43 to 46 °F, but this seems to be an oversimplification. Spawning typically begins with increasing day length and water temperatures rising above 42f (1), other resources state they begin spawning in water as high as 50f (2).

Cutthroat trout are very closely related to rainbow trout, and they share many of the same triggers to determine the start of the spawn, although historically cutthroat trout spawn later than Rainbow trout. Historically speaking cutthroat trout, start to spawn towards the end of the snow melt. This also slowed the chance of hybridization with Rainbows.

Now, that the snowpacks are melting faster, the spawning window is becoming more compact and the overlap between the two species spawning windows is becoming ever greater. This is one of the main reasons why the percentage of hybrids has increased greatly in the last few decades (2).

Young cutthroat trout typically emerge from their eggs in late April.

When do Brown trout spawn?

Brown trout spawn in the fall, with the first trout spawning in late September, with the spawn continuing throughout the fall into December. In very mild years some have been observed spawning into January.

Factors that determine the start of spawning include increasing day length, and water temperature dropping below 48f(1). Increasing flow rate can also encourage reluctant trout to start migrating toward the spawning ground.

I feel a need to mention here that it is difficult to get an exact range for the time of spawning, many websites published temperatures between 43f-53f, but I feel this is and over simplified range. Matthew L. Skoog did research for Bemidji State University and he found that Brown trout were spawning in Straight River at a mean water temperature of only 3.35c (38f), while spawning began when water temperature dropped below 6.36c (43F). (1)

Other research indicated that spawning activity of brown trout had the most success when temperatures were around 3-4°C (38f) (2)

Brown trout eggs incubate in the gravel over winter with the fry typically hatch from April the following spring.

When do Brook trout

Brook trout spawn throughout the months of September, and October (1). Spawning typically takes place when day light starts to lengthen in the spring and temperatures begin to rise.

Water temperature had minimal influence on the time of spawning. With spawning activity occurring as high as 16c (60f). Water temperature has a major influence on spawning intensity and egg viability. For half of eggs to be viable, requires water temperatures below 11.7c (53f), with the optimum temperature being closer to 6c (42f). (2)

After spawning the eggs remain buried in the gravel until hatching in early march.

The compactness of the brook trout spawning season is likely because many populations are restricted to headwater tributaries that remain cool year round. Where populations exist at lower elevations, spawning can be delayed into November.

When do bull trout spawn?

Bull trout spawn from mid-August through to late October once water temperatures have dropped below 9c (48f) with optimal temperatures between 2-4c for egg incubation. Northern populations spawn earlier than more southern ones (1).

Their eggs hatch in early January, and throughout the winter months, the juvenile bull trout fry can be found living in the gravels.

When do lake trout spawn?

Lake trout spawn in the fall, While spawning proper occurs from early October and ends the first week of December, Lake trout become more active from late August onwards, this is believed to be in preparation for the spawn. In some regions, spawning is all by over by the end of October, and most of the lake trout will have begun their migration back towards deeper water (1).

Factors that trigger spawning in lake trout include water temperatures dropping below 55f, and shortening day lengths. Spawning itself does not usually occur until water temperatures are below 50f (2).

Lake trout have a long incubation period with the fry not normally hatching until March the following year.

Do some trout spawn out of season?

I have heard reports of steelheads (rainbow trout) spawning in the fall, I have also heard of brown trout being caught in the spring full of eggs. I have also been told that some strains of rainbow trout spawn at different times of the year. While I am not claiming it is impossible, it does seem extremely unlikely to me.

I have not been able to confirm if any of the above is true, the only example of trout spawning out of season I know about is done in hatcheries and controlled experiments where the staff artificially controlled the water temperature and light exposure. The technique is called artificial photoperiod manipulation.

When do trout spawn at the equator?

Believe it or not, humans have introduced trout into cold water streams in many tropical countries. Some examples that spring to mind include Hawaii, Brazil, and Kenya. There is also natural cherry trout living in Taiwan.

Out of all of these, Kenya is the only country actually on the equator, the others are approximately 1,500 miles away. So, when do the wild trout in Kenya spawn? they do not have differing lengths of daylight to act as a guide.

Trout on the equator can spawn year round, and the main trigger seems to be the onset of rain and raising water levels.

Rainbow trout breeding season in Kenya is not well defined. But it shares more in common with the Spawning season in the southern hemisphere. With a major peak in August and a secondary peak in November. Even though Rainbow trout can spawn year round, there is no evidence that any spawned more than once per year.

While brown trout also seem to have two spawning peaks, spread between a peak in June and another in January. (1) After writing this I can not stop thinking, I wonder if the fabled wild Brownbow, a cross between a brown and rainbow trout could actually occur in Kenya. Food for thought, but this might be a topic for another time.

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