Mosquito fish and koi ponds

How well do mosquito fish and koi play with each other? My current pond
system lay out is like this.

The pump sucks water out of the pond, and dumps the water into the veggie
filter + settling pond. From here a venturi nozzle mixes water and air, and
sends it to the biofilter. Finally the water is dumped into the waterfall
and returned to the pond.

Currently I have mosquito fish in the veg filter. The problem is the suction
on the venturi nozzle is sometimes strong enough to suck a juvenile or fry
mosquito fish into the bio filter. Once they make it to the biofilter, it's
easy to swim into the waterfall and survive the trip to the main pond. I've
attempted to put screens over the drain pipes, but it gets easily clogged
and I'm afraid of the pump overflowing the filter and draining the pond.

Should they make it to the main pond area, how good are koi at population
control? Or am I facing a situation where I will have a mosquito fish pond
instead of a koi pond?
At least if they are in the veg filter, I can regulate the population by
draining the filter, and keeping only a starter brood.

Sameer
--
Sameer

change the two in my email address to a 2, when replying