Aquaponics Use Of Tank Water For Plants

That's the thing, what would be the best plant-to-fish ratio for an aquaponics system to function properly without having to have partial water changes from time to time?

Also, what would be the best species of plants for a tropical climate? I've heard people even growing things like tomatoes and lettuce with this system and this is very interesting for me as I have been asked to work with an NGO in South East Asia and using this technology would be a great addition to our renewable-enegy and renewable-resources project.