As said, the mbuna are the rock dwelling fish of Lake Malawi and their main diet is the algae growth that forms on the rocks. The males have great colouring with your Labidochromis caeruleus being one of them. They tend to be endemic to very small ares of rock and it has happened where divers have removed fish from an area and released them into another area. When buying these you need to make sure you gey some females with males otherwise the males could breed with other similar females resulting in a mixed breed of fish.
It is a great pity you have a hybrid Demasoni/rusty as both these fish should be kept seperate as they are both great fish to keep. Demasoni are basically extinct in the Lake and therefore cross-breeding should be avoided by those who have them. Correct name for the rusty is Iodotropheus sprengerae.
I don't plan on ever giving them away or going to Africa to put them back in the lake or anything, so as long as they don't figure out how to use Orbitz.com to buy plane tickets I think we'll be OK