I wouldn't say all hybrids are necessarily sterile, all you can really do is wait to see if any of your females start getting big. He looks pretty healthy, i'd give him the benefit of the doubt and if after a couple months nothing seems to be happening, that may be your answer. See if he starts courting any of your females, and let us know how that is turning out.
One thing though, is i've found that with lighter colored fish, often if either of the two is darker than the other, the fry will take on the majority of that color. What colors are your females? It's possibly they would mostly look like their mothers seeing as the male doesn't have too much visible color on him, though you may get lucky and have a few that look like him.