I have had a Kribenses for a few months now in a tank with a few other fish... I am pretty sure it is a female... well i had bought a blue johanni for the tank... the johanni seems to be a male... The kribenses puts on a show for the johanni every time he comes around... I was wondering if these two fish will mate together... and if so what should i do to protect the fry from the other fish in the tank

Is the Krib yellow or colored? The females are yellow....
I too have owned both kinds in an aquarium and never noticed any breeding behavior. I doubt that they would. My male krib used to flash off when the others would come near him or bother him.

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IF they did breed and fry hatched.....you can remove them OR just put a lot of small rocks on the bottom in a pile....they will hide in that pile until big enough NOT to get eaten....BUT some will no matter what......I think in this situation its best to let nature take its coarse...strongest will survive

Peace

Is the Male fish showing any interest at all? It would probably just be the female trying to defend her territory. As you said you introduced the johanni after the Krib. Thats my guess. New fish that she doesn't want near her territory. hope this helps