What happens when water temperature doesn’t change. What trigger the spawn?

[MassBass]

The increasing daylight triggers mating and spawning in fish. Reptiles (cold blooded) are also very sensitive to the daylight cycle and start searching for a mate. I think temperature is almost secondary to the increasing light cycle. 

[flyfisher]

On 4/7/2023 at 10:04 AM, MN Fisher said:

Species are adaptable...it's called evolution.

 

If a fish species lives in a body of water that never reaches 'optimum' temperature for what is considered normal spawning temp...whether it's too high or too low...then they'll evolve to breed at the temp that the body of water stabilizes at.

Actually they aren't.  Adaptability is not evolution as evolution is basically becoming a new species entirely.  What you are describing is adaptability much like people who live in colder climates are more tolerant to colder temperatures and vice versa for warmer ones.

 

Animals survive or don't based on the mating and nature has a way of putting all kinds of checks and balances in place to make sure a species lives as long as possible.  Having multiple pieces to the spawning puzzle helps that.

[Jleebesaw]

I'm no expert, but it seems that the water temp thing is a general guideline. I fished bedding smallies on lake champlain 2 days ago. The water temp was ranging from 46degrees to 54 degrees depending on the wind direction relevant to the bay. The main lake is only 43. We got into a feeder river and pounded them in 58 degree water. Anyway, we were seeing snallmouths on beds with a 12 variance of temps. So I'm not too sure about any "rules" that they follow as to when to spawn.

[J Francho]

Since temperature can drastically affect egg development into fry, it stands to argue that reaching optimal temperature conditions plays a large part in the timing.  I know up here during cooler springs, the spawn can be delayed.  I've also noticed that it starts in smaller, shallower waters earlier.  This holds true for prespawn activity as well.