Salmon spawning question

If salmon only spawn in the rivers in which they were born, how did they branch out and end up in so many different rivers? The answer is probably obvious, but it’s late and I’m too lazy to think hard.

Most spawn in the rivers in which they were born, many don’t.

Do you mean: how did they *originally *come from so many rivers? Birds dropped them (or their eggs) there.

ah, alright there we go, thank you both. Yeah that is what I meant I guess. So the behavior is not 100% universal? Is the species old enough to have been around when the landmasses were substantially different, with different inland waterways?

Also, don’t know if it’s taboo to ask another question, but is there any evolutionary relationship between fish ‘scales’ and reptile ‘scales’? I know any common ancestor would probably have to go back hundreds of millions of years, probably before anything I would recognize as either. It may seem like a silly question, but believe it or not I’ve actually never really looked at a reptile up close for more than a few seconds. Unless of course David Icke is correct.

It is a myth that salmon always return to the exact stream in which they were hatched. Most will return there but others stray to nearby rivers and streams. Some only make it to the general estuary. This has been a problem in my area where hatchery bred fish have returned to breed in nearby streams where a wild stock of fish is trying to be restored by leaving the wild stock alone.

In order to protect the wild stock the hatchery fish have to be periodically trapped and killed. Most hatchery bred fish have a tiny wire tag in their snout put there for research purposes. Hatchery fish also have the adipose fin clipped to distinguish them from wild fish so they will be released when caught by a fisherman.

See the final comment in this article:

As I understand it, all salmon intend to return to the exact same place they came from, but if they get lost along the way, they’ll do their mating and egg-laying as best they can. Then the fry have that new place locked in as their ideal destination.

A good rule to remember when dealing with biology: Nothing - NOTHING - is 100%. Including this rule.

There isn’t a salmon species, there are numerous species. Only a small number of species leave freshwater as adults. And even in those species that do, not all individuals leave the freshwater.

The salmon as a group have been around for over 50 million years, which is long enough ago that North America was still connected to Eurasia and not connected to South America, and South Am, Australia and Antractica were still one supercontinent. It was also before the Himalayas started to rise.

So yeah, they’ve seen some major geological reconstruction.

Your thread, you’re allowed to hijack it. You’ll probably get better answers if yiu start another thread though.

It’s a matter of debate.

Some believe that reptiles evolved from fish, and that their scales are truly homologous. That explains where the scales came from, but it has the problem that none of these intermediate fish-reptiles have ever been found.

Others believe that reptiles evolved from advanced amphibians. That seems more plausible insofar as you already have a well developed lineage of terrestrial tetrapods to start from. Unfortunately the advanced amphibians all lacked scales, as do all modern amphibians. So the scales are assumed to have re-evolved independently of fish scales. That seems unsatisfactory and implausible for all sorts of reasons to with the structure and function of scales.