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Subject: Re: (no subject)
From: R C Marelius <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Sat, 11 Mar 2000 13:15:45 -0800
Content-Type:text/plain
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Hello Ann,
Your question is huge!
Here's a few tidbits--since I don't know how much you know, I'm just
assuming you might want interesting things that'll direct you to a tighter
focus.
There are primary and secondary evolution fish.  Primary ones, like most
marine fish, started in the ocean in the environment they're in, that's
where they are now, and they went nowhere else in the meantime.  Secondary
ones, like cichlids, evolved in the ocean then went inland into freshwater,
which required a second evolution.

On ecology, fish are pretty much incapable of maintaining their own
digestive and blood chemistry but depend on the water to permit osmotic
exchanges.  If a fish's water is polluted with waste, not much exchange
takes place.  If the water is really bad, the fish absorb waste from the
water.

On taxonomy--as technology advances, our understanding of connections
between animals changes, so how we classify them changes.  DNA studies are
revamping genera and species placment all over the animal kingdom.  When I
get frustrated at the constant flux of name changes, I remember that
Linnaeus felt that if two animals that looked different they were different
species.  Therefore, it was not uncommon for him to categorize a female and
a male as different species.  While that may seem hilarious to us these
days, it wasn't that many years ago (<25) that Pseudotropheus estherae, a
cichlid species with orange females and blue males, were categorized as two
different species that no one could get to breed in captivity.

On natural selection, another cichlid tidbit (can you tell i'm into
ornamental fish instead of food fish?) is a scale eating fish of the
african rift lakes (Malawi, I think), that goes through cycles of being
right and left "handed", so to speak.  Their mouths are shaped to
facilitate tearing scales of their dinner fish on the right side; after a
few months of this, the dinner fish have wised up and protect themselves.
 The right sided fish don't get food as much, but the left sided fish have
a very easy time for a while, and they flourish and expand; it switches
back and forth continually--natural selection in our time scale.

Charlotte

-----Original Message-----
From:   Ann Seitz [SMTP:[log in to unmask]]
Sent:   Saturday, March 11, 2000 7:23 AM
To:     [log in to unmask]
Subject:        (no subject)

I am inquiring about any information to due with evolution or ecology of
fish.  Like natural selection or taxonmy or cladisitcs.
Thank you,
Ann

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