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RE: observations in Fl. fishroom
I am addressing the reply below as well as that by Gary.
In response to natural and normal ratio being about 50/50 in nature. There
is no way to realistically comment on this. I was out netting killies from
the Arthur kill yesterday. Although they were too small to sex there were
way more fish that got away than those that I caught. Small collections may
be all of one sex but how do we know if they are representative? Males and
females often behave differently. I just hatched a trio of S. Zonatus. The
two females sit by the glass watching me. The male almost never comes out.
If You were netting in the reeds you might come up with lots of males If you
ran a net in the more open water you would more likely find females. I might
note all three hatched the same day. I have seen the same sex based
behavioral differences among lots of different killies. Skewed sex ratios
reported in nature may very well be erroneous.
With regard to there being some advantage to having more females or males,
this is a very unlikely hypothesis. A female killie can lay hundreds even
thousands of eggs during her lifetime just a few could repopulate the entire
species in just a few generations. There is no logical need for there to be
many more females than males to procreate the species. From my experience in
cases where sex ratios get screwed up you are just as likely to wind up with
all males as you are all females.
I too had concluded that there was a reason for skewed ratios. That for some
reason nature wanted more of one sex than another. Then I did the math. And
logically speaking there is no advantage to messing up the mix. 50/50 works
best. And as these ratios are actually obtainable for most killie species
there is no reason to preclude that it is normal.
Now regarding some of the information that we have from fish collectors. I
hate to say it but some of it may be wrong. Some time back I saw a
presentation. There was a photo of a pristine mountain stream. The collector
claimed that the pH was under 4 and the hardness was near 0. Now first of
all, water that soft is very likely to foam when moving as quickly as the
photo depicted. There was no form in the photo. Also I have never seen a
mountain stream with water that soft or acid. Usually mountain streams are
fed by underground sources. The mineral deposits usually make the water
alkaline and/or hard. The test that was taken may have been after a heavy
rain. This would also be supported by the fact that the water was moving
along briskly. I breed some of the fish that were purported to be collected
in such a stream. In pH 7.3 moderately soft water the sex ratio is about 7
to 4 in favor of males, in dead soft acid water the sex ratio is about 80 to
90% males. In this case I am convinced that the data from the collection
site is flawed. Breeding is more than likely done when the water is running
more slowly and is harder or more alkaline. If indeed the readings that were
taken were correct, and I am right about it being after a strong rainfall it
is unlikely that the fish were breeding in the strong current anyway.
When I evaluate the likelihood of any theory being correct without the
appropriate empirical data that I would prefer to have, I usually stick with
the most simple and obvious solution until it is proven wrong. It is much
more likely that by taking the fish from their natural environment and
putting them into fish tanks with commercially processed water that we are
simply screwing up the sexing mechanism rather than triggering some survival
mechanism.
Years back when I was younger there was a theory that was prevalent. It
claimed that every creature lived in a certain niche. I do not know if it is
still popular but it claimed that creatures will function "normally" as long
as the environmental variables remain within a certain set of tolerances.
This is why I work from a starting point that is both moderate and neutral.
Of course species like L. tanganicus come from a niche that is far from
those values and special adjustments need to be done for them.
Your point that there is no one set of parameters that is correct for all
killies is well taken. Here I strongly concur. What is true for Nothos is
most certainly not true for Rivs, or Brackish water Fundulus. Killies come
from all kinds of environments, all different. For convenience sake I use
slightly alkaline and soft water for all of the species I keep. But I do not
keep species that will not do well in the water I mix. For me it is just
more convenient to have one water mix for my entire fish room. I would love
to breed L. tanganicus but until I can do the water I will not do the fish.
Peace,
~RJ~
-----Original Message-----
From: owner-killietalk at aka_org [mailto:owner-killietalk at aka_org]On
Behalf Of José Fabião
Sent: Friday, June 21, 2002 1:33 PM
To: killietalk at aka_org
Subject: Re: observations in Fl. fishroom
----- Original Message -----
From: "Tranquility Base" <TranquilityBase at NetZero_Net>
To: <killietalk at aka_org>
Sent: Friday, June 21, 2002 5:36 PM
Subject: RE: observations in Fl. fishroom
> The normal sexing mechanisms
> in killies will give you an almost perfect 50/50 ratio. Over the past few
> hundred millennia the system, whatever it is has worked a treat in nature.
I agree with your "moderate and neutral" thesis, as a starting point. But
why do you assume that the "natural" sex ratio of killis is 50/50? I suspect
that the wildly different sex ratios we get from time to time are the
consequence of some evolutionary mechanism designed to suit the survival of
the species. When we give our fish the exact (or the closest we can give
them) conditions they evolved in and still get 9/1 male to female ratios, it
may very well be their "natural" sex ratio, and even numbers be the response
to some ecological alarm signal (more females=more eggs in disfavourable
conditions, for example).
Bottom line, we don't understand it. We may reach, through experiment, some
formula that works and gives us even numbers of males and females, but we
won't know WHY it is so. And even if we do come to know how it works for one
species, it will most likely be unique to that species or, at best, its
genus.
Be well,
J L Fabião in (mostly) sunny Portugal
APK 87, KT-35
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