Incubation

[Mitch f]

What gets me is that nature is allowing the eggs to be vulnerable to predators for such a long period of time.

It is what it is, life will find a way

[Chief Grey Bear]

You are right Mitch. It is what it is. And it appears to work. I guess I will just leave it at that.

[Justin Spencer]

My guess for trout is that they adapted a winter spawn to avoid flood events that are more likely to occur other times of the year. Longer incubation due to cold water is the tradeoff for not loosing the entire nest to a flood. The size of the eggs probably lead to a higher survival of young which is the tradeoff for not having as many eggs. Evidently it works as trout haven't gone extinct and are even doing well in some places where they aren't native. Don't pick a fight with nature, we always lose.

[Tim Smith]

It is what it is, life will find a way

I like this comment. Nature finds "a" way but it isn't necessarily the "best" way. The only requirement nature has is that it works.

It's a lot of fun to play adaptationist games as to "why" certain things happen, but the details of history and the constraints of ancestry often play a much more important role in why things are the way they are.

My guess for trout is that they adapted a winter spawn to avoid flood events that are more likely to occur other times of the year. Longer incubation due to cold water is the tradeoff for not loosing the entire nest to a flood. The size of the eggs probably lead to a higher survival of young which is the tradeoff for not having as many eggs. Evidently it works as trout haven't gone extinct and are even doing well in some places where they aren't native. .

The egg-size/egg quantity trade-off that Justin mentions here is a generally accepted evolutionary trade-off (more or less the same quantity/quality trade-off Muddy mentioned earlier).

One problem with the winter flood theory is that in places like the Pacific Northwest, winter floods drive the whole system and most of the spawning happens between October and March. The salmon/steelhead in that region apparently do have the ability to shift spawning timing because a few summer runs occur in that region, but those summer-run systems have the same flood cycle. Something else seems to be driving spawning seasonality.

Pure speculation, but maybe it has to do with a nest versus scattering of the eggs. Perhaps overall the trout eggs aren't as vulnerable to predation.

Both taxa have nests, both undergo egg predation. Centrarchid males guard their eggs and fry over a nest and salmonid females bury most of their eggs in gravel of the "redd" (nest).