I'd say the same thing as stated earlier. A varied diet is a plus. If you're gar is not taking to prepared foods (such as mine), then don't just Feed crappy goldfish. Mix it up. Rosy reds and minnows are fine to me as long as you quarantine them first (you should do this with all fish). But I will not use rosy reds as they are small for a 14" gar. But if you're gar is still a juvenile then I say rosy reds are a good choice.
