Blennies Banded blenny Banded blenny Although Blennies don't have the brilliant color of most saltwater fish, they are a great addition to any aquarium. These fish are on the smaller side, growing to about four inches at maturity. Like Clowns, Blennies are comical, showing distinct personalities. A note: if a fish in this species develops a layer of slime on the body, it's an indicator of stress. It's not pretty, but the slime serves as a natural means of scaring off predators!