Lesbian fishes can have baby???

On monday night, before i bath all the tortoises and fishes, 
i saw one mummy fish die.
Then i saw carefully and i found one baby fish which already die.
There was no daddy fish in the aquarium since december last year.
How come the mummy fish can give birth?
I know the mummy fishes still seem like pregnant, 
but everytime also no baby fish.
But why this mummy fish die and got one baby fish die too?
Where did the baby fish come from?
Weird.