Re: [Killietalk] Couple of questions

[Brian Watters <bwatters at shaw_ca>]

Edd Kray wrote:

>
> Now this is interesting set of posts and an example of why we have to be
> careful with our terminology ("high" "low")
>
> I refer you to a recent article in TFH on water quality in the Amazon. I
> think it was by Wayne Liebel (but don't make me bet on that and I'm not
> going to bother to go look).
>
> He points out that a MAJOR stimulus for spawning behavior in many
> groups of
> Amazon fishes is a lowering of TDS values in the rivers and ponds after a
> rainy period.
>
> So is lowering TDS "a sure fire recipe for disaster"? or do we
> need to be a
> little more specific about the actual values involved?
>
> My opinion, yes going from 1000 to 0 would make many fish at least
> "osmotically uncomfortable" (unless you're a salmon). From 150 to 50 just
> might get them spawning when they weren't before.
>

It is difficult to be quantitative about this but let me put it this way: In
the field (and I am referring to Nothos) I would definitely not use 50 ppm
water for fish that had been in 150 ppm water. They may survive but in my
experience it would stress the fish and would be too risky; one could lose
them.  Keep in mind that we do 100% water changes (when in the field and
trying to change the water in 600 bags late at night one does not have time
to do it gradually). In the particular situation I am referring to, it is
the relative differences in TDS that are critical, and not the absolute
values.

Obviously, in the fish room one can change water gradually over a long
period of time and the fish will probably adapt. On the other hand, to use
an example of going the other way, I have collected fish from 5 ppm water in
Malawi and dumped them straight into Lake Malawi water which, if I remember
correctly, has a TDS of about 300 ppm. This is why, when I lived in Regina
where the water was hard (280 ppm TDS), I could bring wild fish back and
simply dump them staright into my tanks without any "acclimitization"
whatsoever. I know that some of my collecting colleagues who live in areas
where the water is soft have to introduce the fish to their water very
gradually.

I don't know how the Amazon situation works but if the lowering of the TDS
takes place over, say a 48 hour period, yes, the fish may well be able to
acclimatize to it and could even be stimulated by it. Do you know what the
actual change in TDS in the Amazon situation is and how quick is it ? My
comments were based on my experience with Nothobranchius and, as I
mentioned, doing sudden 100% water changes.
________________________________________
Brian Watters
6141 Parkwood Drive
Nanaimo, British Columbia V9T 6A2, Canada
Tel: (250) 760-0564
E-mail: bwatters at shaw_ca

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