RE: Peat

["Brian R. Watters" <bwatters at sk_sympatico.ca>]

Lee Harper wrote:

>
> What is curious to me is the beneficial effect that peat has on reducing
> belly sliders. Obviously it is not a natural material for either South
> American or African soil spawners, yet it provides something
> beneficial that
> we can use to our advantage. Anyone have any ideas on whether it
> is chemical  or physical?
>

This is a question I have pondered for many years without arriving at a
clear explanation. I have also posed the question to KillieTalk at least
once in the last 3 years without any possible conclusions arising. The fact
that peat is quite different in its composition to the natural substrate
would seem to mitigate against an explanation on chemical grounds, such as
the tannin content, but I really don't know. And what physical factors could
there be that would have the effect we observe ?

I think it may be a combination of both physical and "chemical" factors in
that I feel it must have something to do with subtle differences in oxygen
content in the micro-environment immediately surrounding the egg resulting
from its burial in the substrate.

Little or no peat would maximise the oxygen content of the water in contact
with the egg and that is not what occurs in nature because any egg in the
natural habitat that was at the surface or too close to it would probably be
fried by solar heating. If the egg were buried in peat and that peat
compacted around the egg, then perhaps the egg would be subjected to
conditions of slightly lower oxygen content and that triggers the hatching
process. In general, we know that low oxygen content will trigger the
hatching process (and not just for annual eggs). What we also can be
reasonably sure about is that in nature the eggs will hatch within the
substrate where the oxygen content of the water in contact with the egg must
be lower than that in the main body of the water above the substrate.

This may explain why eggs in water without peat often fail to hatch, but how
it would influence the belly-sliding condition, I am not sure. Again, it
seems logical that this is also due in some way to the oxygen content of the
water although, at first glance, the effect would seem to be opposite to
what I have speculated on above. Perhaps for the fry to successfully fill
its swim bladder it needs to hatch in an environment of relatively low
oxygen and then move upwards into an environment of relatively high oxygen
content. Supporting this is the fact that fry will, immediately on hatching,
try to swim upwards to the surface (where the water has a higher oxygen
content). This tendency has led to the (false) assumption that the fry need
to take a gulp of air in order to inflate their swim bladders. We know this
to be incorrect because various experiments have been conducted in which the
fry have been denied access to the surface and to air and they have still
successfully inflated their swim bladders. As I understand it, inflation of
the swim bladder is an internal "osmotic" process. It has also been
suggested that some very small fry may not, in any case, be able to break
the surface tension and actually gulp air (even if that is what they were
trying to do).

When hatching Notho fry, I have occasionally seen the odd fully eyed-up egg
lying directly on top of the peat in the hatching container and these have,
apparently, refused to hatch. This may not mean anything but one could
speculate that these embryos did not hatch because they were not buried in
the peat. When we place the peat in water in a hatching tray, the eggs will
sink immediately and the peat will, more slowly, settle on top of them. So,
most eggs will be at or near the bottom of the peat layer which seems to be
where they should be for optimum results.
___________________________________________
Brian R. Watters
University of Regina
Regina, Sask. S4S 0A2, Canada
Ph: (306) 584-9161 (home); (306) 585-4663 (work)
Fax: (306) 585-5433
E-mail: bwatters at sk_sympatico.ca


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