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Sex ratio manipulation in Nothos
Mike Bleakley wrote that he was interested in the results of Francisco
Casado's sex ratio experiments with Nothos and ask if others have
investigated this theory.
Mike, I'm currently doing effectively the same thing but I'm doing it with
species of the A. elegans complex (also throw in a few Fundulopanchax and
Pachypanchax). It is too early for me to draw any conclusions, but from the
few that have sexed out, I feel it is not a solution for Aphyosemions.
Having said that, if I had a rare species that I was in danger of loosing, I
would try segegrating the fry two by two. The first indications are that
there may be a very slight increase in pair ratios.
The one species I have some data on is A. chaytori SL93/34 (7 sets) and they
are turning out in most cases as pairs (2 pairs and 1 double male), however
this species is new to me and I am not sure that they have a skewed sex
ratio to begin with. I should have a better feel when the other 4 sets sex
out. I previously had one batch of 5 fry raised together and they were 3m
and 2 f. Hardly indicative numbers imho!
I currently have A. christyi (7 sets), A. rectogoense (8 sets), A. cognatum
(2 sets) A. congicum (1 set) and A. schioetzi (3 sets) coming along, plus
about 150 eggs of various species incubating and I expect to conclude my
tests about mid-March or early-April. If the results are significant, I
will submit them to JAKA, if not I'll keep quite and just move on to the
One of the problems working with the elegans complex is getting sufficient
numbers of eggs to generate a meaningful data set. I have further increased
the problem by running sets of 1, 2, 3, and batches of fry. I consider 4 or
more to be a batch.
Mike, I'm not sure any of this has any meaning for a Notho breeder and there
are still other factors that need to be investigated if a serious look is
going to be given into this gender ratio imbalance problem. Some work has
already been done by researchers but most of the studies are in other
genera/families of fish.
Fry Population Density - (that is what we are looking at here) Not aware of
any studies until this one by Francisco Casado.
pH (or water chemistry in total) Rubin,D.A. Copeia, 1985 pp233-235.(pH only)
Temperature Sullivan,J.A. & R.J.Schultz, Evolution, 40(1),1986 pp152-158
Conover,D.O. & B.E.Kynard, Science 213 July 31,1981 pp577-579
Frequency-Dependent Selection Conover,D.O. & D.A.Van Voorhees, Science 250
Dec. 14, 1990 pp1556-1557.
Age of Parents - Not aware of any studies.
Then one would have to look at all of the above factors in ralation to eggs.
Perhaps, while it is generally felt that fish gender is determined after
hatching(There is supposedly some work done on sex ratio by commercial
fisheries however I find no citations of these studies.), there is a need
for adequate proof of this.
Now after all that, I have a question, does anyone have a reasonable
explaination for the basis of this theory of getting pairs by separating the
fry at birth?