Joined: May 2006
|Btw, is a salmon's ability to live in either fresh or salt a year round ability, or does it come and go with their breeding season?|
ask Dr. Science:
salmon posses the ability to be euryhaline (highly tolerant of wide ranges of salinity - the opposite is stenohaline), but really only do a massive shift in physiology to become completely adapated to pure salt or fresh water twice; once when a juvenile entering the ocean, and again when returning back into river systems to breed.
they don't regularly migrate between fresh/salt water.
OTOH, there are several groups of fishes that have many species that do; most live in brackish conditions to begin with.
Poeciliids, for example, have many species that can rapidly adjust to fresh or salt water, like mollys. you can drop a molly into a salt water aquarium and it will adjust its physiology quite rapidly and do just fine.
also, certain species of pufferfish, sturgeon, and herring are some other examples.
sharks/rays also contain some species which regularly migrate between fresh and salt water, most notably the bull shark (Carcharhinus leucas). The bull shark has been known to attack humans far up several river systems, for example the Zambezi (Africa), Brisbane (Australia), and Ganges (India). It's even found in Lake Nicaragua (central America).
The way sharks cope physiologically with rapid changes in salinity is far different from the way most bony fishes handle it. However, that's a story for a different time.
back to your regularly scheduled programming.
|So it only took 6,000 years for hammerhead sharks to evolve from salmon?|
that's equivalent to saying:
so it only took 6000 years for alligators to evolve from chameleons?
if you don't know why that is just SO wrong, ask lenny.
actually, it's even worse than that; there's not a big enough schism in the reptile group to cover a bony fish evolving into cartilaginous one.
maybe spider monkey->kangaroo might be a better comparison.
"And the sea will grant each man new hope..."