Re: [RML] Fw: Male or Female Kubutu Rainbowfishes (Melanotaenia lacustris)?

Gary Lange (gwlange at stlnet.com)
Tue, 17 Mar 1998 22:11:33 -0600

I guess my thoughts are with "environmental" as far as sex ratios go too (for
rainbows). Some bows seem very succeptible to a high population, one way or
the other but I don't think it has to do with temperature but rather pH. I
mentioned Uwe Romer's work with Apistos before because he had dispelled the
myth amoungst dwarf cichlid keepers that it was the pH. He showed that it was
absolutely temperature. I think the temperatures I filed in my mind (for his
work were 23, 25 and 27). 23 produced mainly females, 25 even mix and 27 90%
males. Cichlid keepers always keep their fish too hot & therefore end up with
more males. His data tables were from something like 300 spawns I think. It
really seemed like solid work.

I raise a lot of fry at 80-85 degrees and when I am "watching the tanks" I
don't have any problems with sex ratios. If I get lazy and don't do small
water changes, especially in crowded tanks the tanks get quite acidic (ph 5-6,
yellow on the bromthymol blue scale). My KH is only 3 degrees (~ 54 ppm) so
without a little bicarbonate help it can drop very quickly. A small amount of
bicarb will act as a buffer an keep your pH in a reasonable range. When the pH
drops in my tanks, I get mainly males. Since I really don't push the pH up
with excessive bicarb (or carbonate) or other additives I really don't see
excess females. This has been reported by others who have been on very hard
water systems (read high pH). Since most hobbyists here in the states seem to
only report GH the numbers I hear are 250 ppm and higher where this has
occurred. We'll just have to assume that the KH is also much higher. These
are usually clubs where they also raise a lot of Afreakin cichlids which is
usually a giveaway for hard water conditions (read high pH).

I think also that Adrian made a very good observation in one of the ANGFA
articles on how one can also get mainly males. The short version is: males
grow quicker, females become fodder.. I think his example was boesemani. I
grew 3 really nice rubrostriatas onces out of a group of 50 :-) found out what
was going on when I saw a tail sticking out of one of the larger fish. To
avoid this remove your "tear-aways" to another tank.

Gary Lange
gwlange at STLNET.com
Rainbowfish Study Group of North America
http://home.stlnet.com/~gwlange/rainbowfish.index.html

----------
> From: Adrian R. Tappin <atappin at ecn.net.au>
> To: rainbowfish at pcug.org.au
> Subject: Re: [RML] Fw: Male or Female Kubutu Rainbowfishes (Melanotaenia
lacustris)?
> Date: Monday, March 16, 1998 1:33 PM
>
> At 07:46 16/03/98 -0700, Julie wrote:
>
> >My experiences w/ raising G. ramuensis is more like a 60/40 to 70/30
> >split, but the majority were males to the best of my recollection.
>
> Julie, by any chance did you record your water temperature and pH when you
> spawn your fish?
>
> I think there has to be something, probably environmental, that causes this
> as I often have this happen. Sometimes its the other way round and I end up
> with mostly males. It would be interesting to find out what it is.
>
> Adrian.
> ...............................................................
> Adrian R. Tappin
> "Home of the Rainbowfish"
> http://www.ecn.net.au/~atappin/home.htm
> ...............................................................
>