Survival of the fittest?

One of my fishtanks uses a standard mechanical filter, meaning water gets sucked in through a propellor, it moves through a chamber containing a sponge and gets blown out through small holes.
I also have guppies in the tank, who as you may know, breed like bunnies.
Every time there’s a new batch of fry popping out it now seems that pretty much the only survivors are the small fry that are dumb enough to swim near the intake of the filter, get sucked in and avoid getting chopped to pieces by the propellor. They survive in the chamber that contains the filter.
The other fry in the tank usually get eaten.
So as far as my little 54 liter corner of the animal kingdom goes; evolution favors the lucky and the dumb, the strong and fit get eaten.

Work in progress... not home!
Trying to get all/most of the new code working before I start on the eyecandy.