Now for the most part these are not needed in an aquaponics system. Mosquito are only going to lay eggs where the water is really still and in most aquaponics systems that is really rare. However, for those rare occasions that one might find they need to keep mosquito from breeding, (like maybe a duckweed pool) Mosquito dunks will do the job. I have used them in systems with fish and had no ill effects. They use a bacteria that are specific to certain kinds of larva so only affect those kinds of larva and not other creatures.
6 pack of Dunks