I believe that they breed in mud holes/caves in the water which is impossible to do in an aquarium. You could try putting them into a natural pond (one with mud sides instead of pond liner) and just leave them alone. I really don't think its an easy task in a controlled environment, if even possible, but if you are able to get things natural as possible I think they should breed on there own without any aid from you. Also I am pretty sure they ONLY breed in the spring.