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[Killietalk] Temperature and the number of vertebrae
Recently we had a discussion on the potential effect of temperature on
the number of vertebrae in fish, in the context of whether temperature
effects could account for the marked shortening of the body length that
a few of us have seen in offspring. I indicated that I had found a paper
on this topic in Nature (May 16th, 1959). I have now obtained that paper
(actually a very short letter) and below summarize the results published:
1. The literature cited indicates that the belief at the time was that
lower temperatures actually INCREASE the number of vertebrae. These
studies included the killifish Fundulus heteroclitus.
2. Another cited study done in Salmo trutta trutta had found that the
lowest average number of vertebrae occurred at an intermediate
temperature, with both higher and lower temperatures resulting in an
increased average number of vertebrae.
3. The author (Itazawa) repeated the experiment using Channa argus
(snakeheads), incubating eggs at different controlled temperatures. He
confirmed the finding that the highest number of vertebrae occurred at
intermediate temperatures, the number falling off for both high and low
4. Note that the range of vertebral numbers that he found were from 56
to 62, but there was extensive overlap. The differences in AVERAGE
vertebral number from a large number of hatchlings examined (a total of
roughly 4500) were less than one vertebrae. Thus, the effects were small
and wouldn't, in my opinion, be noticeable as a marked decrease in the
length of the fish.
Note also that this effect is one of the effect of temperature
variations during the development of the egg, not the growth of the fry.
Some hobbyists have postulated that the shortening effect might be due
to effects of lower temperature during the growth of the fry. This is
possible, but could not, in my mind, be due to an effect on vertebral
number. Low temperatures could effect the growth in length of the
vertebrae, which potentially could have a large effect on total length
of the fish. The reason I make that speculation is that modest effects
on all the vertebrae would be cumulative and more likely to produce a
noticeable effect that the addition or loss of one vertebra.
In summary, I think we are still without an explanation for the short
back effect that some hobbyists have experienced.
Barry J. Cooper
Sweet Home, OR 97386
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