Re: NANFA-L-- Review of Suckers in North America

Subject: Re: NANFA-L-- Review of Suckers in North America
From: Peter Unmack (peter.lists at)
Date: Tue Oct 12 2004 - 12:46:16 CDT

This bounced to me due to a bad keyword, just forwarding it along with
the key word modified.

From: "Joshua L. Wiegert" <JLW at>
To: <nanfa-l at>
Subject: Re: NANFA-L-- Review of Suckers in North America
Date: Tue, 12 Oct 2004 13:36:11 -0400

Yes, and no, Moon.

A given fish has 1000 offspring, of which only, say 990 are able to
survive under the best circumstances. The other 1% (10 fish) have various
genes which make them unzuitable for survival -- whether it be cricked
spines and other physiological phenotypes or behavioural ones. Ideally,
they get eaten day one. And, of course chance and less important genetic
differences eliminate about 900 of the other offspring before they can
reproduce. This is the same whether it's fish or frogs or any other "mass
producer." Whereas our 1% might have behavioural genes that give them
outright stupid behaviour (Hey! Watch this, I can swim right into that
turtles mouth!), the others might have behaviour that works out. For
instance, it seems rather stupid for a minnow to swim at a pike, right?
Yet, in Guppies, this behaviour is what keeps them alive in many
populations -- sexual selection selects males with bright colours, and in
order to avoid being preyed on, they have to charge pike cichlids and
other predators, which keeps them off balance. So, sometimes "stupid"
works (especially when sexual selection is involved. :)

When you remove any sort of selection pressure to remove those other fish --
both the 1% and the others which would naturally be removed -- their genes
can be expressed more highly in the F2 generation (with them being the F1).
Artifical selection factors -- whether purposeful or not -- are going to
favour some of our "stupid" fish. Which bass will get more food ? The one
who lurks under a log, acting like a wild bass, or the one who comes rushing
to the surface at feeding time, like an Oscar? Which one is thus more
likely to survive an outbreak of Ich, or Velvet? Which one is going to
produce more spawn in the F2 generation?

Further, fish do "learn" behaviour. One of the typical arguements about
releasing salmon is that the farmed/hatchery raised Salmon are stupid and
have bad habits, and rather than learning good habits and smarts from teh
wild ones, the wild ones learn the bad habits. Just like people, I suppose
(and, admittedly, thats personifying the fish.) Yet, think about it. Get a
bunch of Domestic Fish, Zebra Danios, for instance, that rush over to the
top of the tank every time you come by. Mix a bunch of some kind of minnow
in with them and see if they don't start doing that a lot faster. I've used
that trick to get finicky fish to eat -- you put something in there that
eats -everything- in sight, but wont' steal all the food, and they "teach"
the finicky fish to eat.

If this behaviour is genetically selected for, and you've released adults
which are beyond predation size (for the most part), they'll pass this on to
their offspring. Even if it's not, they may "teach" the other adults, which
are also beyond typical predation size, this kind of behaviour.

The last thing to consider on releasing fish is disease, which I haven't
seen brought up yet. I'm not talking about the typical "released fish might
carry disease" gambit. The fish which are captive raised are exposed to
crowding, often poor conditions, and a number of diseases. As such,
selection pressures on them for disease can be higher than in the wild.
Meaning that the captive fish are more resistant to disease than their wild
cousins. This becomes exagerated as generations go on. (At the same time,
selection can go the OTHER way if they're kept in very sterile conditions.
For example, guppies from the East are very poor and have destroyed the
Guppy's reputation for hardiness. Yet, pond raised swordtails from Florida
are very resilient.) This is part of the reason why we often have more
disease problems with wild fish than captive raised fish. As a result, the
released fish, once in the wild, are more resilient to some diseases and,
ironically, better equiped to survive.

However, since they're not kept in natural conditions, they do aviod some
parasites and diseases that require an intermediate host, as well as some
they just never happen to encounter. This lowers their immunity, and may
result in die-off of the released fish. I'm not aware of which direction
the pressures go, or if ti simply varies from species to species, or if it's
even significant in either direction.


Joshua L. Wiegert
JLW at
AIM UID: JoshuaWiegert                                                ICQ
UIN: 276060292
Feel free to contact me by any of the above means for any reason.
I'm sorry for not communicating more frequently, but sometimes its hard to
write on a moving planet.
   - Ashleigh Brilliant

The things that come to those that wait may be the things left by those who got there first.

Wise men talk because they have something to say; fools, because they have to say something. -- Plato

Due to budget cuts, the light at the end of the tunnel has been discontinued. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=-=-=-=-=-=-=-=-=-=-=-= ----- Original Message ----- From: <Moontanman at> To: <nanfa-l at> Sent: Tuesday, October 12, 2004 12:39 PM Subject: Re: NANFA-L-- Review of Suckers in North America

> In a message dated 10/12/04 12:08:46 PM Eastern Daylight Time, > dlmcneely at writes: > > >> Natural selection for success in hatcheries? Less genotypic variability? >> Hatchery fish are the progeny of a restricted set of parents compared to >> wild >> fish. >> >> > > So what you are saying is that if you catch two fish and breed them their > progeny will be less able to survive than the young of two fish who have > stayed > in the wild? Isn't that a little bit like saying that if you raise rats > and cut > off their tails each time eventually the rats will have shorter tails? > > moon >

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: Fri Dec 31 2004 - 11:27:44 CST