That is not moss. LOL It is a form of hair algae that has been grown to form mats. These are extremely benficial to fry raising. They eat up any excess ammonia which helps when feeding heavily and helps reduce the amount of water changes on sensitive fry tanks. This is the first time I have used this method and I have noticed a big reduction in fry loss and a higher rate of growth compared to my previous spawns.
I am pretty sure that is one of the month old fry in the tank. I have a mixture of 3 spawns in that tank at the moment. 2 month old fry, month old fry, and 2 week old fry are all in there together.