Hi there,
on our annual IRG conventionin June 1996 in Wuppertal we also had deformed M. praecox for offer.
Unfortunately this was seen by the buyer not before he was at home. The praecox had very short or nearly
lacking dorsal fins.
I think that deformations in rainbowfish - as in many other fish - may have several reasons.
Inbreeding may be one reason for deformations. However, genetic defects which may be seen clearly
and in most of an offspring don't occur very often. Until today I have seen this only in guppies.
However, due to environmental influences eggs can be influenced and mutations can develop. These are
genetic defects, but they are caused by the fish's environment. There may be several impacts like heavy
metals, pecticides, but also this kind of stuff many breeders use as they think they would care for the fish
with: water addenda like Tetra aqua safe or similar chemistry which contains EDTA. It is a fact that EDTA
influences fry development in the egg at least in the Zebra Danio. However, it nowhere is published as the
aquarium magazines which could publish it are afraid (and not without reason) that they would get less
advertisments. In Germany EDTA is one of the largest problems in water pollution and tap water
preparation for drinking purposes. However, aquarists throw it into the water in tons.
Fish tuberculosis may also have similar occurence than genetic defects, e.g. body deforming.
In nature deformed fishes normally have less chance to survive and to breed. Thus they become rooted out
within one generation if they have survived long enough (what most don't). However, in the aquarium many
people try to raise up even the last fish tail. I think this is the main reason: money. We don't have the same
conditions in aquarium and in nature. Natural selection does nearly not occur in aquaria. There breeders
have to select instead of nature.
Last note: If you've bought deformed fishes already you may make a breeding attempt as not necessarily
the offspring must show the same deformations. If they have, don't make a second and don't dare to bring
any deformed fishes into the market if you are a serious breeder :-<
I hope this answers a few questions.
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