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"Sam" (yungfamily at sympatico_ca) wrote....
> Subject: Re: KillieTalk Digest V2 #269 (N. foerschi)
> At the beginning of the year, I did my grade 8 science project on the
> affect of pH on the sex of N. foerschi. I hatched a batch of about 40
> fry in normal tap water (approx. pH: 7.2, total hardness: 90 ppm).
> After a week, I separated half the fishes into water w/ a pH of 6.4 nd
> the other half into water w/ a pH of 8.4. (used sodium phosphate to
> lower pH and baking soda to raise it). The water in the lower pH tank
> had pH: 6.4, total hardness: 90 ppm. The water in the higher pH tank
> had pH: 8.4, total hardness: 90 ppm. I tested the water in the tanks
> every 4 days, and tried to keep the chemistry in the tanks from changing
> throughout the experiment. I "controlled" as many variables as I could
> think of, and everything I did to one tank of fishes was done to the
> other. After about 8 weeks, I counted 1 male : 19 females in the tank
> w/ the 8.4 pH. In the 6.4 pH tank, I counted 5 males : 14 females. If
> you take the results at face value, it means that the 8.4 pH produced a
> sex ratio of 1 male to 19 females, and the 6.4 pH produced a sex ratio
> of 1 male to about 3 females. Incidently, the males raised in the 6.4
> pH showed better colouring and more vigour. Just wanted to tell my
> experiences w/ the whole sex ratio thing.
An interesting experiment. An interesting follow-up would be to see what the
results would be if, for example, every specimen in both batches was raised
in its own separate container (see my comments below).
The water in my tanks is invariably alkaline - it comes out of the tap at
about pH 8.1 and may drop to about 7.5 depending on how much peat I have in
the tank, how many fish are in the tank, etc. Except for the first few days
after hatching, I always raise my fry in bare tanks (little or no peat) so
the water remains alkaline. I also invariably get more males than females
(see further comments below).
Lilia Stepanova wrote.....
> Subject: Re: Sex ratios and water
> Here is some info from book published in Russian (A.S.Polonskii
> "Soderjanie i razvedenie aquariumnih rib", 1991).
> "Temperature and chemical composition of the water can affect sex ratio
> in the fry of Cyprinodontidae. For example, at t=22-25 C most of the fry
> will be females, if the temperature is not constant, most of the fry will
> be males. At the same pH=6.0, E.dageti will have more female offspring
> (>90%) in the soft water (dH about 5 degrees), in the hard water (dH 24)
> about 90% of fry will be males. A.gabunense in the acidic water (pH 5.0)
> will give more females, at higher pH=6.5 - more males."
I would also be interested to know about other factors involved in these
experiments (e.g. population density, were the experiments repeated, etc.)
and what the controls were. However, this information appears not to be
I am sure it has not escaped the attention of many of you that the results
of Polonskii's experiments, at least so far as pH are concerned, are
opposite to those reported by "Sam", which underlines the point that this
whole question of sex ratio in killies is far from that simple. There are a
large number of factors that should be taken into account.
I find some aspects of Polonskii's statement rather ambiguous in that he
claims that "at t=22-25 C most fry will be females". Does he mean any
constant temperature within that range or temperatures fluctuating within
that range ? And, if he means the latter then that would appear to
contradict the statement that temperatures that are not constant will favor
the production of males. I would be interested to know what sort of a
temperature range he regards as "not constant" - greater than a 22 to 25 C
variation ? He also suggests that soft water will result in "more female
offspring". More than what ?
Assuming that the sex of the fry is determined at or shortly after hatching
(which may not be the case), then this latter observation about soft water
is contrary to what I have experienced in my fish-room. While I keep my
adult Nothos in hard alkaline water, my fry are hatched and raised in
moderately soft water (about 80-100 ppm TDS) until about the time they start
to color up. They certainly don't change sex after I switch them over to
harder water and yet I still get a dominance of males in most cases (see
below for exceptions).
As I have said before, I don't think that the answer to skewed sex ratios
lies in a single simple factor such as pH (or temperature). While I have
certainly not conducted controlled experiments in this respect, one
observation that I have been able to make consistently over the years is
that if I raise a large batch of Nothos (or South American annuals for that
matter) under fairly crowded conditions, I invariably get a large dominance
of males. I also don't believe that in my situation this is a matter of the
faster growing males killing off the slower growing, and therefore smaller,
females. In contrast, smaller batches raised under less cramped conditions
usually (but not always) produce more even sex ratios.
As an extreme example of the latter situation, I always raise my N.
ocellatus fry individually, each specimen to its own tank, from within a few
hours of hatching. I do this because of the extreme aggressiveness of this
species (the fry are also ultra-cannibalistic). I always get fairly even sex
ratios with this species; it may vary to a small extent from batch to batch
but overall the sex ratio is essentially 50:50 males to females.
As I mentioned in an earlier communication, I am of the opinion, therefore,
that environmental conditions in relation to population density may be a
primary factor in determining sex ratio. Of course, one critical question,
as George Slusarczuk has already pointed out, is at what point in the
reproductive process is the sex of the embryo or the fish determined ? I
have discussed this matter with biologists and it seems that, in fish at any
rate, this is simply not known. Apparently, it seems likely that it can
happen at various times in the process, depending on environmental
conditions. This unknown factor alone introduces a variable that makes it
very difficult to conduct controlled experiments. Certainly, controlled
experiments are possible but to be meaningful in any way they would have to
be extremely comprehensive and as a consequence, quite complex.
Brian R. Watters
University of Regina
Regina, Saskatchewan S4S 0A2, Canada
Ph: (306) 584-9161 (home); (306) 585-4663 (work)
Fax: (306) 585-5433
E-mail: bwatters at sk_sympatico.ca