by Dr. Klaus M. Stiefel
When you dive in the reefs of Cabilao, you will see a multitude of colorful, curiously shaped tropical fishes. You will see fast-swimming parrotfish, surgeonfish and fusiliers, calmly schooling snappers and sweetlips as well as solitary groupers and wrasses. These are mid-sized to big reef fishes which catch divers’ eyes right away. But it’s also worth slowing down and inspecting all the corals and rocks on Cabilao’s dive sites more closely to discover some of the smaller, hidden reef fishes. Among them are the beautiful and fascinating blennies.
What is a Blenny?
Blennies are small, bottom living fishes – scientists call them cryptobenthic fishes, where crypto- stands for “hidden”, as in crypto currency, and benthic means “bottom living”. A total of 401 species of blennies are known to marine biologists, most of which live in the ocean, while a few blennies are also at home in brackish and freshwater as well.
Most blennies are smaller than 10 centimeters in length, and live alone or in small groups. If you look closely, you will see little “antlers” on the heads of most blennies, called “cirri”. In other species, blennies have a crest in the top of their heads. The function of these cirri and crests is not completely understood, but they are likely there to show off, just like actual deer antlers or the decorative tail feathers of a peacock. At least in some species of blennies, the females chose their male mates by assessing how nice his head appendages looks.
If you took a blenny out of the ocean and put it under a microscope, you would also see that in contrast to most other fishes they have no scales on their bodies. Furthermore, blennies don’t have a swim bladder, the gas filled sack in a fish’s body which provides buoyancy control just like a BC does for a diver. Since blennies mostly perch on rocks or corals and rarely swim in mid-water, they don’t need one.
Blennies show a lot of character – they tend to be inquisitive fishes which come to check out new objects or creatures. Very often you will see them approach and inspect divers, and frequently blennies live in the discarded products of human civilization such as empty beer bottles.
How to Photograph Blennies
As so often in underwater photography, patience and good buoyancy are the keys to success. As mentioned, many blennies will often be curious, and even approach divers. Then you can get shots like this one, where a blenny decided to hide out on my arm, under my dive computer!
In general, however, blennies are small fishes and that small size makes them rightfully act carefully as well – they balance the caution with the curiosity. This makes a careful approach by the underwater photographer necessary. If you spot an interesting blenny a few meters away, perched on top of on a coral, you have to swim towards it slowly, and without flailing your arms and hands. If you spook it, it might retreat in a crevice and not come out for some time, and your chance to photograph it during that dive will be wasted.
Fang blennies are among the larger blennies, up to about 10 centimeters long, and, as their name implies, boast a mighty pair of fangs in their jaws. Divers who harass such a fang blenny have been bitten, and the experience is akin to being poked with a sharp needle. These blennies will defend themselves, but not attack on their own, and are in fact a lot of fun to watch. Fang blennies like anchor lines, and during your safety stops along such lines you’ll have the chance to observe them up close.
Where to Look Next
I hope this blog post has gotten you excited about blennies! There are a number of great resources online where you can learn more about these fascinating small fishes. I can recommend the Blenny Watcher site, run by Ned and Anna DeLoach, two seasoned underwater naturalists who have dedicated their attention to blennies for many years. Great footage of blennies and other underwater life!
Of course FishBase is always a great resource for all things fish, it’s a database dedicated to unifying much of the information which is known about each and every fish species. This is their overview page for all blennies, and this is the FishBase page with a thumbnail per species of blenny.
If you’d like to go fully scientific, this is a great recent overview article about the biology of small fishes on coral reefs which like to hide (“cryptobenthic fishes”):
What is not a Blenny?
Very often when discussing blennies with other divers they ask me “what is the difference between a blenny and a goby?”. Gobies, of course, are the other major group of small, abundant bottom living fishes which populate coral reefs.
So, how do you keep them apart? One hint is the posture: blennies often perch on rocks or corals with their bodies curved to one side, while gobies’ bodies remain straight most of the time. Also, gobies like to crawl in the sand, and occasionally occupy burrows dug under the sand, while blennies like to hide in holes in rocks or corals, or in the aforementioned anthropogenic garbage. The other giveaway are the curious cirri on the heads of the blennies, which gobies don’t have.
Another family of fishes which is occasionally mistaken for blennies are the tripplefins, similarly small fishes which perch on rocks and invertebrates. A tripplefin roughly looks like a goby with three dorsal fins.
Some Blennies you are likely to encounter in Cabilao:
These are among the pretties blennies, small fishes with square heads and a variety of curious yellow, red, brown and black patterns on their bodies. Fishbase lists 53 species of Ecsenius. Old-timers are telling me that these blennies used to be abundant in the Philippines, which they aren’t anymore, but if you are patient you will still be able to find them on rocks and corals, usually in the shallower parts of dive sites.
False Cleaner Wrasse Blenny
This is probably the most curious of all blennies, and to tell it’s story, it’s necessary to take a step back and talk about reef fishes and parasites. You, as a land-based human, might occasionally be pesked by parasites such as mosquitoes or ticks. They usually don’t constitute a major health hazard for you. The situation is different for reef fishes, which are heavily burdened by parasites, mostly by tiny blood-sucking crustaceans.
To get these parasites removed, the reef fish visit a number of specialized cleaner animals, like the well-known cleaner wrasses and the banded cleaner shrimp. These pick the parasites off the fish bodies and eat them; the cleaner animal gets a rich meal from the parasite, and the client fish is relieved from the infestation. Both sides win.
Now, the false cleaner wrasse blenny is an unusually devious fish: it pretends to be a cleaner wrasse, by mimicking its coloration and swimming pattern. Unsuspecting parasite-infested fishes approach it to get cleaned, but the false cleaner wrasse blenny doesn’t remove any parasites, but rather bites the fish and feeds on its scales, skin or mucous. This is as if a person pretends to be a dentist but in fact is out to steal your gold crowns out of your mouth. Evil? It sounds like it, but you can’t judge a fish by human moral standards!
Look for the false cleaner wrasse blenny around coral outcroppings and prominent rocks, in the same spots as you would find cleaner wrasses. Look carefully at the fish’s mouth to distinguish the real from the false cleaner wrasse.
The author is a biologist, underwater photographer and popular science writer currently based in the Philippines. Check out Klaus’ social media presence as Pacificklaus on Twitter, Facebook, Flickr and Instagram. His new book “Gobies of the Tropics” is scheduled for publication with Fata Morgana Press this summer.