In one of the companies I worked for in the past had a journal club related
to reproductive biology, being some what of a maverick in this group I
prtesented some work on sex change in fish, instead of some sort of
domesticated animal like pigs. I forget the exact biological terms but there
are two mechanisms for sex change in animals one of which is like the clown
fish which go from male to female - if dominant female dies the local male
becomes female, and one ofthe other non-determinate fish in colony becomes
male, if the male dies one of the non-determinate fish becomes male and the
female remains female. Now on the other hand you have what has been proposed
in DG's - this the females can become male which is just the opposite of the
clownfish. Then there are these marine groupers that spawn alternately as
male and female within the same spawning ritual . . . That is a little more
kinky than the DG's.
Scott Buckel (RSG)
--------------------------------------
Date: 5/29/96 8:26 AM
To: Scott Buckel
From: rainbowfish at pcug.org.au
On Wed, 29 May 1996, Bruce Hansen wrote:
> We have certainly had a good response so far to the Calcium for fry =
> topic. I wonder if Peter could contact some of the hobbyists from his =
> "survey" of American breeders that resulted in his conclusion that =
> nobody over there uses calcium :-) Perhaps the shellgrit was hiding =
Yer yer, alright, I was wrong. Hey, but at least I got a response
out of 'em! :-) (The YankEEs that is....)
> for this species. Similarly for Desert Gobies, it seems that adding =
> calcium (in whatever form) and salt (up to the equivalent of seawater) =
> improves the sex ratios towards equality whereas a vast oversupply of =
> females seems to be common in situations where thet are raised in =
I would question the number of females as it doesn't pay for males to
show colour when a dominant one will beat them up for it. Safer to look
like a female (dull) than be killed. And anyway, if they change sex so
readily should that be a problem? Sex ratios vary in the wild according
to data from John Glover's masters thesis. Johnson's no. 3 bore pool,
males varied from 28.7 to 45.8% of the population, Nunns bore was the
opposite, males making up between 62.6 to 72.8 % although one sample in the
middle contained only 34.1% males.Blanche cup, 61.7 to 71.5% males, Wobna
Spring 41.2 to 58.4% males, Freeling Springs 54.5% males, Blyth Bore
58.1% males. Most sample sizes were between ~500 and 2000. Most of
these sites probably have high Ca levels as they are depositing
travertine fairly actively. In addition the water is typically hard and
alkaline. Are Edgbaston gobies any different? They live in springs
which are typically soft although quite alkaline. Calcium values vary
from 2-6 mg/L (that would be 2-6 ppm wouldn't it?). pH is up around 8
typically due to close to stuarated bicarbonate. However, there is no
data on wild pops and no one bothers to keep them in catpivity. Be an
interesting comparison though.
> softish neutral to acid water. While we are on the subject of DG's, has =
> anyone else seen the phenomenon of sex reversal occurring? A few times =
> when left with a group of females only in a tank of DGs one of the =
> larger specimens has become a functional male and gone on to breerd =
> successfully. These particular males never became as brilliantly =
> coloured as the primary males.
Questions.
1/ Have these newly developed males ever been proven functional females?
2/ How do most people sex desert gobies? Typically colour correct? Not
a very reliable characteristic. Be much better to look at their
urogenital papilla. How many folks do that?
I have heard this from a few sources but never with much confidence. Rob
Wager thought he had it pinned down but could not replicate his results
when he tried it accurately. I plan on running some breeding
experiements to try to figure out if they really do change sex once I
build up my stocks.
>Asimilar process occurs in many marine fishes such as the anemonefishes etc.
What you describe and what happens in Pomacentridae is actually
quite different. According to Julie Zeppieri the largest fish in the
school is the female, when she dies the largest male becomes a female.
There are other details too that are important in the differentiation but I
hate marine fish and refuse to look it up.... :-)
Tootles
Peter Unmack