Is there anyway to tell whether a rooster is fertile or not?
well, if you crack open the egg and look at the blastodisc, you can tell if the egg is fertile. But some young ones are fertile but haven't gotten the knack of mating so it may take awhile for the eggs to show fertility.
Check out my thread here for details: https://www.backyardchickens.com/t/16008/how-to-tell-a-fertile-vs-infertile-egg-pictures