But then how are they aware of those conditions Also, the preference usually is more on the side of where they're born vs optimal proper placement

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chmod775 10 months ago | parent [-]

Nice water flows downstream, terminates in the ocean. They simply follow it back upstream.

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jagged-chisel 10 months ago | parent | next [-]

I’m with you on this. Found some tasty water? Swim towards it. It gets tastier the further we go? Keep going.

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rightbyte 10 months ago | parent | next [-]

So how do they find the river outlet into the ocean? There surely is some bird compass thing involved. I am only half joking when I write that Venus guides them.

That nature works at all is astonishing.

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jaggederest 10 months ago | parent | next [-]

It's all chemoception, the same as with single cell organisms. They swim towards a saline gradient ( which they can taste, for sure ) and follow it up into fresher and fresher water.

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bad_haircut72 10 months ago | parent | prev [-]

Word gets around? Animals probably have way better communication than we think. One crab says to a friendly eel "hey dont tell those damn Salmon but this estuary is good again" and before you know it, everyone's favourite restaurant is booked out till March.

	▲	cruffle_duffle 10 months ago \| parent [-]
		I used to go to this estuary until it became too crowded.

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monknomo 10 months ago | parent | prev [-]

Yeah, no need to make this complicated.

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Angostura 10 months ago | parent | prev [-]

Thanks, I was bang my head on this one, until you suggested a nice simple solution