I've always heard that males have bigger mouths than the females. This is necessary because the males have to guard the nest/eggs/fry and will inhale and crush to death bluegill, frogs, turtles, and anything he thinks will harm his offspring with his mouth. I'm not sure if I'm sold on this or not though. Males don't usually get over 6-8 pounds max and are usually leaner especially during the spawn because all of his efforts are spent on protecting the nest. Female bass fatten up prespawn to nourish the developing eggs, they find a male's nest they like, lay their eggs, they may stick around for a few days and then they leave. Males create the nest in tjd sand with their tails, fertilize the eggs, guard the eggs and then guard the fry for a month or so. It's no wonder the males are smaller!