Thanks all for the nice responses!
I am a little worried about the older fry though.

He turned out to be a real bully to his little brothers. It is unbelievable how this fish can already be so territorial at this age!

He spends most of his time pushing his smaller brothers out of "his" cave (well, from his point of view it IS indeed his).
I placed another small cave to give the smaller fry some rest, but they are just like sheep, they want to be where the others are.
I am still thinking of a solution and a little worried that the bigger fry could harm the smaller ones.
Does anyone experience with fry agression?
I think my bigger fry is from november 2004 (I have to look it up), do you think that I could already release it in the big tank, without risk that is starves?
I think that the wisest solution is buying a second fry trap, and having to seperate the fry
