Blennies are generally small fish, with long bodies, large eyes and big mouths. They have an amazing character about them and are an excellent edition to the aquarium. Some have great cleaning abilities like the lawn mover blenny that will graze on the green algae on your glass leaving kiss marks around your aquarium. Other perch themselves on rock ledges and come in and out of little holes within the rock work of the aquarium. There are many types of blennies and each have their own characteristic.