Depends on the fish, small sunnies and such will eat them, keep the tanks well aerated which will also help with the high temp. days and surface motion like from a powerhead discourages mosquitos from egg laying, if it is still a problem make or buy a tank cover like for a lizard tank, made from plastic mesh window screen, they can't lay eggs in water they can't reach. Watch out for racoon and possums. When I was in Leesville I lost a couple tubs of sunnies and bullheads that way, racoon snack bar.