For starters are your females receptive? You would know by the change in their resting coloration. They should be a nice pink/salmon color if they are receptive. Secondly, males can be unwilling to breed for numerous reasons. It could be dietary? (Like a vit a def) Or it could be enviromental, he may need to be spurred on by the presence of a rival male to get his blood going so to speak. Or depending on the locale he may have a shorter breeding season each yr than some of the other locales do. You have to know the animals body language/coloration and the specifics of the locale your working with.