# Salmon spawning question
**URL:** https://boards.straightdope.com/t/salmon-spawning-question/511494
**Category:** Factual Questions
**Created:** [September 25, 2009, 7:36am UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494 "2009-09-25T07:36:19Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@YourAdHere](https://boards.straightdope.com/u/YourAdHere)
#### Post date: [September 25, 2009, 7:36am UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/1 "2009-09-25T07:36:19Z")
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.
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### Author:  [@Blake](https://boards.straightdope.com/u/Blake)
#### Post date: [September 25, 2009, 7:54am UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/2 "2009-09-25T07:54:25Z")
Most spawn in the rivers in which they were born, many don’t.
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### Author:  [@panache45](https://boards.straightdope.com/u/panache45)
#### Post date: [September 25, 2009, 8:20am UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/3 "2009-09-25T08:20:10Z")
Do you mean: how did they \*originally \*come from so many rivers? Birds dropped them (or their eggs) there.
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### Author:  [@YourAdHere](https://boards.straightdope.com/u/YourAdHere)
#### Post date: [September 25, 2009, 10:31am UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/4 "2009-09-25T10:31:20Z")
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.
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### Author:  [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)
#### Post date: [September 25, 2009, 5:08pm UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/5 "2009-09-25T17:08:15Z")
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:
> **[How do spawning fish navigate back to the very same stream where they were born?](https://www.scientificamerican.com/article/how-do-spawning-fish-navigate-back/)**
>
> The University of Montana's Megan McPhee answers
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### Author:  [@dracoi](https://boards.straightdope.com/u/dracoi)
#### Post date: [September 25, 2009, 7:43pm UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/6 "2009-09-25T19:43:10Z")
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.
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [September 25, 2009, 7:48pm UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/7 "2009-09-25T19:48:47Z")
> [@YourAdHere](#):
>
> So the behavior is not 100% universal?
A good rule to remember when dealing with biology: Nothing - _NOTHING_ - is 100%. Including this rule.
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### Author:  [@Blake](https://boards.straightdope.com/u/Blake)
#### Post date: [September 26, 2009, 9:55am UTC](https://boards.straightdope.com/t/salmon-spawning-question/511494/8 "2009-09-26T09:55:31Z")
> [@](#):
>
> Is the species old enough to have been around when the landmasses were substantially different, with different inland waterways?
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.
> [@YourAdHere](#):
>
> Also, don’t know if it’s taboo to ask another question..
Your thread, you’re allowed to hijack it. You’ll probably get better answers if yiu start another thread though.
> [@](#):
>
> but is there any evolutionary relationship between fish ‘scales’ and reptile ‘scales’?
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.