[Zbrafish] Breeding more females than males?

Kim via zbrafish%40net.bio.net (by kvanvugt81 from gmail.com)
Mon Aug 8 12:35:25 EST 2011

Hi everyone. My name is Kim and I work in a zebrafish lab in the

I have a question about breeding:
All our lines (mutant and wildtype) are breeding great. We use the
small breedingtanks with dividers from Technilab.
But lately we have noticed that there are more females than males in
our young fish ( about 75% more females). Now we started to wonder if
that is normal or not.

We collect the eggs in the morning and keep them the first 5 days in a
petridish(about 50 eggs a dish) in a incubator at 27.5C. We change the
eggwater every day and after 5 days we place them back in the system
( about 100-150 larvea per tank= 3,5l) and let the water inlet place
little drops of water in the tank.

>From what we have read, the young fish can change from male to female
and reverse till they are a month old. So you need to place a lot of
small fish in a tank (so check, I think). And to grow more males the
amount of O2 has to be lower than normal ( I think with drops of water
instead of a normal waterflow should cover that too?)

Does anyone have a tip for me and do you experience this to and is it
just normal?
Thanks in advance!

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