Uh oh...you had to ask, JW!!!
Blennies are popular amongst salt water aquarists. Some are caught by anglers now and then. Most of them are bottom dwellers. Some are found in tide pools, coral reefs, and in my home state in the Chesapeake Bay, they are found in oyster beds. IMO, I think that they are one of the most comical and interesting fish in marine aquaria. They sit on the bottom on their modified pectoral fins and move around the tank from perch to perch, patrolling their territory and looking for food, or warding off invaders. They're very alert with eyes that are constantly checking out anything and everything...they're very curious.
I've posted a pic below of a blenny found in my home state (Hypsoblennius hentzi, or the feather blenny). Notice that the pectoral fins are very large and the rays of the fins are very thick, perfect for sitting on the bottom or a piece of coral. Their eyes are located on the upper part of their head, perfect for bifocal vision and nabbing morsals that drift overhead. Above their eyes are soft branching fleshy protuberances called cirri. As far as I know, nobody knows exactly what these are for. They can become quite ornate in some species (not all of them have them though). Most species don't have a swim bladder and sit on the bottom. They don't sit for long though, they are very active. The next picture below is of another blenny...and I have a neat story behind that one too.
And, some have swim bladders and delicate pectoral fins, like this one:
There is a fish called a cleaner wrasse (first picture) that, in the Pacific tropical coral reefs, sets up "cleaning stations". Various species, like groupers, angelfish, triggerfish, just about any kind, line up to be cleaned by these little colorful wrasses. These fish dart in and out of their customers mouths, behind fins, around the tails, under the bellies, searching for and eating parasites that they may find. This is a famous case in ichthyology (the study of fishes) of symbiotic behavior, or symbiosis. The host and visitor each benefit from the relationship. The host (or customer) gets cleaned and the cleaner wrasse gets easy meals. Often the hosts are much larger and could easily gulp their little cleaner, but they don't. It's really amazing. Well, for every good thing there's always someone that's going to take advantage of the situation and ruin it for everyone...
...enter the saber toothed blenny (second picture and third picture). This fish is a mimic of the cleaner wrasse. Very similar in color and behavior, even down to the "bouncing" swimming motion of the wrasse (both species use their pectoral fins almost exclusively for propulsion). This fish sets up a cleaning station much like the cleaner wrasse trying to lure larger fish in. When a fish comes in to be cleaned and poses for it's "fishicure", the saber toothed blenny darts in and out of the fishes gills and around the back to the tail and takes a big bite of flesh of the tail of it's "customer", or more appropriately, it's victim. The saber toothed blenny obviously swims away in a hurry as to save it's life and not risk becoming a meal of it's angry victim. Most fish recognize the good guy from the bad guy here. The victims of the saber toothed blenny are often young and inexperienced fish. Here are the pics:
Here's a cleaner wrasse working on a grouper going in it's mouth:
Saber toothed blenny in hiding. Notice the mouth is underneath the nose. The cleaner wrasses mouth is at the end of it's nose:
Saber toothed blenny out and about up to no good:
Here's a pic of a kid catching a blenny:
This site has lots of good pics:
http://ourworld.compuserve.com/homepages/BMLSS/Blenny.htmSorry for hijacking this thread...but isn't this interesting?
