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Water in Notho habitats
I am reluctant to become involved in this discussion on water conditions in
Notho habitats but, since I have collected from and/or examined a large
number of such pools, I feel I can perhaps clarify some of the issues being
discussed.
As already pointed out by Barry, the water in the majority of Notho habitats
is "cloudy". Actually, a better word for this property would be "turbid"
because it is due primarily to suspended particles of clay. In some cases, a
certain amount of algae may be a contributing factor but suspended clay
particles represent by far the most important cause of the turbidity.
Note that in the above I wrote that the water in the MAJORITY of Notho
habitats is turbid. As always, there are exceptions. I have collected Nothos
from pools where the water ranged from essentially zero turbidity to those
where the water had so much mud in suspension that it had the consistency of
thin chocolate sauce. The typical Notho habitat falls somewhere between
these extremes although perhaps biased toward the more highly turbid side of
the spectrum.
Now, before anyone misinterprets what I am saying here, let me hasten to add
that of the 400 or so Notho locations that I have looked at, only about half
a dozen had very clear water. I remember one exceptionally clear pool
(Benga, Malawi, 1988) where I could literally see the bottom through a depth
of about 1 meter of water. Invariably, those pools that have relatively
clear water also have thick vegetation which, presumably, limits the amount
of mud substrate that is exposed and also tends to bind it.
The most turbid (muddiest) water is usually (but not always !) found in the
more open pools where cattle and/or wild animals come to drink, so the
substrate is stirred up at frequent intervals creating, in some instances, a
real "soup". Some of this water really is very muddy and one can, for
example, place a 3" Notho in a 4" bag in such water and except for the
occasional glimpse you would not be able to see the fish. Incidentally,
under such conditions the fish don't do very well in bags (it affects their
respiration) so we always have clean, clear water on hand to place the fish
into when we catch them and when we bag them up in the field.
Again, as Barry has already pointed out, muddy or turbid water does not
necessarily mean "dirty" or polluted, and usually doesn't. In fact, the
water in most Notho habitats is, biologically and chemically, relatively
uncontaminated. Pools that are scummy and have foul smelling water very
rarely contain Nothos which cannot survive in such excessively polluted
water. In the field, we are able to almost always recognise such pools and
don't waste too much time in them. Incidentally, pools having such foul
smelling water are not necessarily polluted due to human activities; they
simply become stagnant by natural causes.
In some Notho pools one will find evidence of cow or elephant fecal matter
but in such quantities that this is hardly likely to pollute the water
excessively. Much of this material is simply processed vegetation anyway and
the biological system operating in the habitat can cope with that.
Occasionally one finds evidence of human excrement but the occurrence of
that in Notho habitats has probably been very much overstated. Remember that
the locals also have to be able to walk around in the area and many of them
actually use the water in Notho pools for washing, etc., so they don't
simply defecate anywhere and everywhere. (You may wonder how they use such
muddy water for washing; well, they allow it to stand so that at least some
of the suspended material settles out.)
While Nothos can survive perfectly well in very turbid water in their
natural environment, they don't do so well in that same muddy water in the
confines of a plastic bag - nor would they in our tanks. The natural
habitats represent vastly larger physical and biological systems with a MUCH
lower population density than we maintain in our tanks - in most cases by a
factor of many thousands. The natural pools also have a larger surface area
per volume allowing the water to maintain a reasonable oxygen level. The
conditions in a natural system simply cannot be replicated in our fish-rooms
and it is not just a matter of scale, although that is a major factor.
Tyrone wrote:
>
> I'm told that ........... the
> expressed colour of the resident fish is a function of
> the turbidity. Muddy pond = dull fish, clear pond =
> bright fish = bird food. Murky pond = nice fish.
>
It is a bit more complex than that. We have collected fabulously coloured
Nothos in waters representing the full spectrum of turbidity. In 1988 I
collected beautiful N. sp. Benga from perfectly clear water and stunningly
coloured N. kirki "Chiuta" from what could best be described as a mud soup.
It was difficult to imagine how the latter could have survived in the
"water" they were in but they were like little orange jewels. On the same
trip I collected very nicely coloured N. kirki "Chilwa" from moderately
turbid water in pools in a non-flowing stream course. In another pool, not
connected directly to the "stream" pools but only about 30 meters away, I
collected the same Notho but the males were almost completely devoid of
colour. They were in perfect health and even larger than the others, and
after a week or so in my tanks these pale specimens had also developed good
colour and one could not tell them apart.
What was the difference in the water of the two habitats ? While both
habitats contained moderately turbid water, that in the pool hosting the
pale fish had a very bright, almost milky turbidity. Subsequently, I have
seen the correlation between very pale Nothos and water having this bright
"milky" turbidity on many occasions. It is not easy for me to describe the
appearance of this water and to the untrained eye there may be no obvious
difference; however, we have got to the point where we can see such water
and reliably predict that the fish will be pale.
Why the fish become pale in such water is another matter and I don't think I
can give an unequivocal answer - so I will leave it at that.
The water in most Notho pools is still. However, here again, there are
exceptions. Many Notho pools occur adjacent to flowing streams and there may
be a connection between the still pools and the flowing water. The Nothos
may be found in both the still and the (slow) flowing water. Perhaps they
end up in the flowing water by accident. I have collected N. sp. Mansa (in
Zambia) in water that was flowing quite strongly. The fish were concentrated
along the margins of the stream channels where the flow was slowest;
however, I even caught some in the middle of the channels where the flow was
so strong that one had to wade with care. I collected N. symoensi in a
swampy area through which the water (also relatively clear) was flowing in
certain channels through the heavy vegetation. Notably, the Nothos were
concentrated away from these flowing parts of the swamp so obviously
preferred the still water.
___________________________________________
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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