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RE: fish food - population density

Hi Scott,

I have H. Formosa in a 2.5 gal tank with some java moss and water sprite A
single Giant Japanese pond snail and its occasional offspring keep the tank
algae free. There is a heater and a corner filter. There are about 10 fish
in that tank. There have been about 10 fish in that setup for over a year.
There are always fry, but the population never goes up. As a mature fish
dies it is replaced. When the population is at max no fry make it to
adulthood.  I have seen this before with other fish.

I have also seen that if you over populate a tank on purpose due to a space
shortage. Some form of illness usually comes around and wipes out just
enough fish to reestablish some form of equilibrium.

Maybe some fish are better at handling overpopulation than some more
"intelligent" species. Just an observation. I am not looking to endorse
cannibalism or start a new off topic thread.

Best regards,


~RJ~

-----Original Message-----
From: owner-killietalk at aka_org [mailto:owner-killietalk at aka_org]On
Behalf Of Scott Davis
Sent: Friday, August 10, 2001 10:54 AM
To: killietalk at aka_org
Subject: Re: fish food - population density


Hi Bill,

You put an interesting perspective on it. Since I posted that suggestion
alluded to below, I've been reading George Barlow's The Cichlid Fishes:
Natures Grand Experiment in Evolution. Comparing some small number of
cichlid situations where a lion takes over a pride and kills the cubs so
that the females go into heat and produce his cubs, he notes some situations
where male cichlids might indeed do that. The idea (not really *occurring*
to them) would be to insure the spread and survival of that males genetic
material. Those are just a few of the myriad spawning and care situations he
described. His big thing is cichlids developing an advantage over their
competitors - a Darwinian advantage - will lead to different spawning
strategies and behaviors.

That book, which I'm slowly chewing on, understanding more slowly, is
available on clearance from www.hamiltonbooks.com for $20, not a lot off of
the regular $28. However hamiltonbooks is a book renderer and those titles
are going out of print - even though Barlow's book was c. 1999!

I still wonder if there are not times when that food+space+ shelter formula
will work. In larger tanks I've had a lot of fry hanging our in the
shrubbery over several pairs of Ep. kassiapluensis (or what ever it is this
decade) in a  20 gallon tank. In another 20 with three pairs of lineatus
(notorious fry eaters), up among one huge tank dominating Java fern, I
pulled a dozen 3/4" youngsters. I seem to remember similar experiences in a
10 with gar Misaje and dageti where they gang spawned over generations.
(Possibly senior moments but I think those cases happened.)

Your concept of parental fry recognition in a single paired tank was
graphically illustrated to me one day when squirting some daphnia into a 2.5
gallon tank with a large (well fed) pair of gardneri Jos Plateau and a dozen
fry who had just grown up in there with them. Mom roared out from under her
mop to snarf down the daphnia. An overly adventurous young'un came charging
out to see what was going on and made the mistake of swimming in front of
momma. She grabbed the fry, checked, turned her head and spit him/her out
and went back to her feeding frenzy. The little one shook himself (come to
think of it, he had to be male, he didn't ask for directions) and put-putted
off to a safer corner.

"One of these days", probably months yet to come, I will evict a colony of
wild green swordtails from a living room 40, clean up the mess
(affectionately known as the green hell) and install a couple of pairs of
golden australe. I'll keep your thoughts in mind. If they are mostly smaller
than the breeders (much as in a Lamprologus/Neolamprologus brichardi/
pulcher colony is where only the really larger members get evicted or in a
tank - shoved in the corners) then your hypothesis will apply. If there are
more big ones which grow up and we still get fry then maybe the pond is big
enough for another pattern to take place.

There are probably other explanations for why some fry remain and some
don't. Killies have often been accused of not reading the book.

I provoked a spirited response from the legendary James Langhammer on the
livebearer list some time back by recommending that one remove a certain
number of fry from the parents and he most forcefully suggested that
approach to fry care  was improper and would lead the less interesting and
desirable community patterns. My response was if an idiot (such as myself)
is raising them, who gets into a school year where a work week (counting
paper shuffling and phone calls)  often consumes 70 hours of his time, fish
get neglected and even benign livebearers may either eat their young or at
least out compete them for such food as there is. He evidentially has been
so complete in caring for his fish that the idea of neglecting them and the
consequences of that neglect were pretty much out of his experience!

A neat thing about this, is you've got my jaded curiosity up. Maybe I will
get around to establishing that tank. Maybe also a couple of others, as time
permits.

Thank you for taking the trouble to respond. I agree that your hypothesis
applies in many situations. (Almost always, I start a new tank with just a
pair of killies.) Certainly I've seen a second female eating eggs. (Although
in the case of a reverse trio there may be more fry in a  natural set
because the dominant male spends more of his time hassling the lesser male
and not pestering the female.) We may have to agree to disagree in some
instances. It's stuff like this (and thoughtful correspondents like
yourself) which keeps the hobby interesting.

Thanks and all the best!

Scott

> Hi Scott.  It is more than just that.  A single pair= fry ignored.  Add
just
> a third or 4th fish = NO fry.  With gardneri you can watch a second female
> following the pair and eating the eggs.  Seems almost like a breeding pair
> know they are having fry and non breeding single or multiple fish present
> just know food when they see it.  It is not just in the numbers and food
> availability.
> Bill Shenefelt
> ----- Original Message -----
> From: "Scott Davis" <unclescott at prodigy_net>
> To: <killietalk at aka_org>
> Sent: Wednesday, August 08, 2001 9:36 AM
> Subject: Re: fish food
>
>
> > This is the population equilibrium thing. In nature or an aquarium if
> there
> > are no alternative foods for adults one can expect that they may prey on
> > fry. One wonders if there is not enough food for the adults if it makes
> > *sense* to have more hungry mouths of a species around which will
starve.
> > Better to return the protein to the adults for later.
>
>
>
> ---------------
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