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Re: Nijsseni temperature.
Here I go again. Römer's study on sex ratios shows that for A. nijsseni, a
temperature of 26ºC (79ºF) and pH 5.5 for the first 2 - 4 weeks will result in a
50/50 ratio of males to females. His graphs show that at a temperature of 23ºC
(73.5ºF) only 15% will be males if raised in a pH of 4.5, 10% in pH 5.5, and
about 5% in pH 6.5. At 26ºC, 60% will be males at pH 4.5, 50% at pH 5.5, and 45%
at pH 6.5. At 29ºC (84ºF), 95% will be males at pH 4.5, 85% at pH 5.5, and 75% at
pH 6.5. So you see, temperature is much more important than pH in determining sex
ratios.
The following is a translation of de Rham's (the discoverer) and Kullander's (the
describer) 1982 paper (Apistogramma nijsseni Kullander un nouveau Cichlidé nain
pour l'aquarium. Rev. fr. Aquariol. 9(4): 97-104). This is the first description
of the male A. nijsseni. The original description used only females. It also
describes the history behind when, where, how, and why this species got into the
hobby, its biotope, and what fish were found living with it. Yes, ASG members can
get copies of this paper and its translation from me.
"An analysis of the place was made by a Peruvian limnologist, on 1/9/81 at 12:30,
yielding the following results:
Air temperature: 29ºC (84ºF) CO2: 0.9 ppm
Water temperature 25ºC (77ºF) Total hardness: 7.5 (!!!!)
Conductivity 14 µS/cm Temporary hardness: 0.03º
pH: 5.6 (probably more acidic) Calcium: 0.5 ppm
02: 6.45 ppm Chlorine: 1.6 ppm"
These values appear to match Römer's very closely, but remember water values vary
with the seasons so these might not be the same as those during their normal
breeding season. Here is an indication that total hardness isn't as important as
carbonate hardness for blackwater fish. Compare the above values with those
below, given by Linke & Staeck in their book:
Date & time: 6/28/83, 5:00 pm Total hardness: <1º dH
Air temperature: not given Carbonate (temporary)
hardness: <1ºdH
Water temperature: 27.5ºC (81.5ºF)
Conductivity 3 µS/cm
Things change with the seasons.
Hope this helps.
Mike Wise
Douglas Dunlop wrote:
> I have some Nijsseni which are my pride and joy. I have always kept them at
> around 73 F with the temperature in the summer going up as high as 80F. I
> usually induce them to spawn by creating the "rainy season" by doing a water
> change with about 30% tank volume of 68 F water. I have recently read of
> someone who bred them at significantly higher temperatures (84F). Does
> anyone have any data from actual collection sites that would suggest which
> water temperature is most appropriate?
> Doug
>
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