Originally Posted by
hobbit6003
Hi Ron and all,
In my opinion, such developmental anomaly nearly right from the onset of birth, can only be due to a genetic predisposition.
My opinion tends to differ, Kenny. While there may be some tendency for one strain or collection to react more dramatically to external toxins or injury, deformities like those shown are usually induced by some external insult or hybridization (outcrossing, not inbreeding).
Whilst metal toxins can cause such a spinal deformities (both scoliosis and kyphosis), you'd probably find that some other concurrent batches of frys would have contained them, and not just to a certain batch/batches.
Of course, if the frys are born alright and slowly develop spinal deformities, there're other considerations, such as nutrient deficiencies or disease (eg. fish TB).
As for fluctuation to water temp causing this, I've yet come across any literature mentioning such an occurence, nor can I think of how this can cause deformities to days old frys.
Kwek Leong, did the manual of yours mention if the fluctuation is a seasonal or a diurnal (day and night) fluctuation?
Untergasser also says that keeping fish at the wrong temperature or sudden fluctuations can cause injury like this.
As for a genetic cause, such an inheritance of the so-called 'bad' genes, is usually due to excessive in-breeding, resulting in the expression of defective genes within a grossly diminished gene pool.
In killifish this is almost never a cause, IMHO. 95% of killifish are in such restricted locations and numbers that they are already highly inbred and defective genes have long since weeded themselves out. Inbreeding gets a bad name for mostly cultural reasons, but it is outcrossing (hybridization) that can induce the worst deformities, like parrot fish.
Inbreeding can certainly increase the expression frequency of a recessive defect, but that is a rarity in killifish. Such defects may arise spontaneously by mutation, but the effect is rarely a bent spine. Usually it is a color or pattern variation, or a reproductive failure of some kind, IME.
Inbreeding is a most useful tool for eliminating hybrid genes and for setting a desirable color or pattern. I sort of hate to see blanket condemnation of it among those making choices of brood stock. It is another useful tool for the breeder, when properly understood.
In our wild-type killies, I like to see maintenance of as broad a gene pool as is practical, so we keep them with what they started with as much as possible. Most went through a genetic bottleneck when collected and introduced. It behooves us to keep as much of what is left as we can.
We also have many "aquarium strains" so there are lots of species to tinker with, for those who have an uncontrolled desire to "improve" them.
Some select for albinism, and some go for a purer color or bigger fins. That doesn't happen very well, without deliberate inbreeding and line breeding. Those never cause defects, and only very rarely cause an unexpected recessive to appear. Knowing it is present is the first step to eliminating it.
HTH
Wright
01 760 872-3995
805 Valley West Circle
Bishop, CA 93514 USA
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I've lost all 17 of the remaining fry and all had the bent-spine problem before they died. The weirdest bit is that my Simp. flammeus fry are OK, and these have been housed in containers with water that is at least pH 7.4 which is very much the standard pH for most of my tanks with the exceptions of those with ADA Aquasoil in them. Those have hit pH levels of 6.0 and have somewhat stabilised. 
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