RE: [Killietalk] Cool water killies and related considerations

["Brian R. Watters" <bwatters at sasktel_net>]

Lee harper wrote:

>
> In a message dated 1/6/05 11:11:00 PM, bwatters at sasktel_net writes:
>
> << I am not sufficiently familiar with the rainfall pattern in So. America
> to argue with you. >>
>
> I don't think we are arguing. My point was that rainfall in the
> autumn (April
> to June) causes a rise in the water table and some flooding which in turn
> begins the swimming phase of the annual killifish cycle. There
> may be other
> periods when they are submerged, but winter is a major period
> when they are
> actively growing and breeding and thus they are definitely cold
> water fish. I was
> reporting my own observations in the field about water
> temperature. That was the
> beginning and still is the title of this thread.
>

To some extent, I think we are talking at cross purposes. My involvement in
this thread started when I questioned the comment made by Curtis Smith that
"......  their summer (our winter) is the dry season in
Argentina and Uruguay when the pools dry up......."

There is a mountain of indisputable climate data to show that this is
incorrect. The summer months (our winter months) in Argentina and Uruguay
are the wettest months, in terms of rainfall.

If I interpret the climate data and your comments correctly, the situation
for that region would be as follows:

The increased rainfall starts to build up in October reaching a high during
December-March. Following March, there is a fairly sharp decline and
July-August are the driest months. The build-up in the water table will take
place over a number of months and is mainly due to the rainfall during the
period December-March (rather than April to June as you suggest because
these are relatively dry months ?). The water table will, however, remain
high through the early part of the dry season because it lowers slowly.
August is a good time to collect because the water table is still high
enough to maintain pools of surface water and the fish have already hatched
and grown to a decent size. August will also be relatively cool because by
then it is the winter season. To use the same example as I did in my last
message (the town of Rosario), the average air temperature in August is 11.4
C (the coolest month is July at 10.1 C) whereas the warmest month is January
at 24 C. Obviously, there will be some regional variations depending on
local geography.

The situation is analogous in most respects to East and Southeast Africa. To
take Malawi as an example, the rainfall season may start in
November-December, reach a peak in February and by April the rains have
ended. The best time to collect Nothos is late March-April at the end of the
rainy season or the start of the dry season, when the water table is still
high enough so that there are pools, the fish have grown to a reasonable
size, the roads are mainly dry and one does not get rained on every day.
Many of the seasonal pools will persist into June. The hottest months in
Malawi coincide with the peak period of rainfall so, by April it is already
starting to cool down. However, the difference between East Africa and
Argentina-Uruguay is that the former is at or close to the equator so that
the differences between summer and winter temperatures are not as great.

One thing that intrigues me about the Argentina-Uruguay situation is that
while the temperatures are relatively very low at the time the fish are
present in the pools, the temperatures that prevail during the incubation
period of the eggs is substantially higher. This is not the case for
conditions to which Notho habitats are subjected. The other interesting fact
is that in that part of So. America there is still a significant amount of
rainfall during the "dry" season. While this is not enough to maintain the
surface pools that constitute annual fish habitats, nevertheless, the soil
moisture content must be much higher than it is in Notho habitats during the
"dry" season. In East and Southeast Africa the distinction between the wet
and dry seasons is generally much more profound.
___________________________________________
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 sasktel_net



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