Parrotfish Cocoon

Parrotfish sleeping in a mucous cocoonRecently, during a get-together of diver friends, the subject of parrotfish cocoons came up – I don’t remember why – and surprisingly, several said they had never seen a parrotfish sleeping in a mucous cocoon. After thinking about it, Ned and I realized that in all the hundreds of night dives we’d made, we had only seen it maybe a half dozen times. We encountered it for the first time in the mid-90s off Key Largo while waiting for the coral to spawn. We didn’t see the coral spawn that night, but the parrotfish cocoon made our dive. Mucus, secreted from a gland below the operculum, enveloped the sleeping fish in a protective bubble. And until about four years ago, all I knew about this phenomenon was what was taught when I first started night diving: that the mucous cocoon prevented attacks from nighttime predators like moray eels, by masking the scent of the sleeping fish. That theory was proposed in the 1950s by the scientist (H.E. Winn) who originally described the mucous cocoon of parrotfishes.

In November 2010, marine researchers from the University of Queensland published their findings that proposed another theory behind the mystery of the fishy cocoons: the nighttime covering provides protections from blood-sucking parasites. In tests, when exposed to parasites, 95% of the fish not protected by cocoons were attacked while only 10% of those in cocoons were. They point out that this theory doesn’t have to be mutually exclusive with the moray eel predator theory.

Parrotfishes and some species in the related wrasse family sleep at night by bedding down directly on the sand or in holes in the reef, making them ideal targets for parasites that would have a more difficult time attaching to a swimming fish. Although we’ve only seen parrotfishes in cocoons, wrasses like the Bluestreak Cleaner Wrasse (Labroides dimidiatus) and some in the genus Pseudocheilinus have been observed sleeping in mucous cocoons both in the wild and in aquariums.

I have posted a short video on our Blennywatcher YouTube channel or you can watch it below. (Note: We originally wrote about this in our June 2011 Critter Hunt column in Scuba Diving Magazine).


Fangblenny baring its fangs

This is why they are called Fangblennies (video frame capture)

This is why they are called Fangblennies! Dr. William Smith-Vaniz’s 1976 monograph, The Saber-toothed Blennies, Tribe Nemophini, was a must-read when we started diving in the Indo-Pacific many years ago, but it was the cover of his publication (see below) showing the recurved canine teeth of the lower jaw, that turned these cute little reef fish into the stuff of nightmares and inspired my quest to see them for myself.

Blenny in a bottle - Petroscirtes brevicepsSaber-toothed, a.k.a., fangblennies, with the exception of one species in the eastern Pacific, are found in the Indo-Pacific. Unlike other blennies, most saber-toothed blennies have a swim bladder and can often be seen swimming up in the water column. They get their common name from the well developed, backward pointing canine teeth in their lower jaw that are used for defense.

The Saber-toothed Blennies, Tribe Nemophini by Dr. William Smith-Vaniz

The Saber-toothed Blennies, Tribe Nemophini by Dr. William Smith-Vaniz, cover image used with permission

In addition to describing these blennies, Bill collaborated on research of mimetic relationships among blennies and tested the toxicity of fangblenny bites by inducing a couple of different species to bite him on the midriff and arm – yeow! It was noted in one of his papers, “The few people who have accidentally or deliberately been bitten by a Meiacanthus experienced only mild pain, but swelling surrounding the site of the fang punctures indicated a biological response disproportional to the mechanical injury.” That’s all I needed to read to know that this was not the way I wanted to see fangs – blenny wrangling was out and stalking became the name of the game. Roger Steene has a classic shot of a blenny baring its fangs so I knew it was possible to see it, I just didn’t know it would take me 12 years!

I’ve had tantalizing glimpses of the fangs of other species, but this Petroscirtes (I’m pretty sure it is P. breviceps, the Shorthead Fangblenny) living in a bottle in Lembeh Strait, is the closest I have come. It gave me one quick snap and it was enough to get the video frame capture used at the beginning of this post.  Ned is still trying to capture this with his camera but you can see from the video, how fast he’ll have to be to get it.  You can watch the entire, very quick encounter on this video on our Blennywatcher YouTube channel:


Mimetic Relationships Involving Fishes of the Family Blenniidae, Springer, Victor G., Smith-Vaniz, William F.

Meiacanthus urostigma, a New Fangblenny from the Northeastern Indian Ocean, with Discussion and Examples of Mimicry in species of Meiacanthus (Teleostei: Blenniidae: Nemophini).  Smith-Vaniz, William F.,  Satapoomin, Ukkrit, Allen, Gerald R.

Carry Crab Mystery

Carry crab with hydromedusa from Lembeh Ned DeLoachWhat is this Carry Crab carrying? It was a mystery to us for a week. The common name, carry crab (sometimes called carrier crab) applies to crabs in several families that disguise themselves by using modified back legs to grip things like, well, like just about anything. In previous posts, we showed photos and video of a crab carrying a sea pen, one carrying a banana peel and even a crab carrying a live nudibranch. I’ve circled the crab, in case you can’t make it out:Carry crab2 with hydromedusa from Lembeh Ned DeLoach

And here is another one with an Upside-down Jellyfish (Cassiopeia):

Carry crab w:jellyfish Ned DeLoach

Carry Crab (Ethusa sp.) carrying an upside-down jellyfish (Cassiopeia sp.) for shelter

The carry crab with the mystery cargo was pointed out to us by our dive guide, Man, near the end of a dive on a black sand site in Lembeh Strait. As the crab scurried, whatever it was carrying pulsed a little, reminiscent of a jellyfish but it had curlicues and wispy tentacles so it didn’t quite look like the jellyfish we usually see. What was it? Have a look at the video at the end of this post and you’ll see what we saw. The following week, during Ned’s slide show about the animals he has seen during his open water night drifts, our answer appeared on the screen. It was a hydromedusa, a type of jellyfish. In manipulating the animal to make it easy to carry, our little crab had wadded up the hydromedusa, making it difficult for us to identify. Comparing it to this intact, free-floating animal the answer was obvious:Hydromedusa in open water by Ned DeLoach

Here is the video from our Blennywatcher YouTube channel:

Nudibranch Preying on a Goby

Nudibranch on Goby Fiji Ned DeLoach

The first time we saw this was in Fiji

Here’s another strange one: A nudibranch that attaches to and eats the fins of shrimp gobies! Shrimp gobies are cool fishes – teaming up with nearsighted burrow-building shrimp, the vigilant gobies act as sentinels, watching for danger, while the shrimp build communal burrows. Life is good out on the sand flat, right? Well yes, until the little nudibranch, Gymnodoris nigricolor, enters the scene.  In the photo, the nudibranch is the little black job hanging onto the fin of the goby.

We were diving in Lembeh back in 2000 when Mary Jane Adams told us about this relationship of the nudibranch on the goby and asked if we had ever seen it in Lembeh. She had recently seen it in the Solomon Islands, which was a range extension, since at that time, it had only been reported from Okinawa. We didn’t even know such a relationship existed, but our guide said he had seen it once at a site called Critter Hunt, so off we all went in search of it.

No luck in Lembeh but in 2005, I found it in Fiji (which I think was the first time it had been recorded there) – but of course at the end of a dive and 65′ deep. Ned got a shot but the goby spooked and darted into its hole, taking the nudibranch with it. We weren’t sure if the nudi would still be hanging on when the goby re-emerged but our allowed dive time was over so we couldn’t stay around to find out. I marked the spot with a very distinctive rock and we planned a second dive so a couple of others could photograph it. A comedy of errors ensued – mainly because I didn’t realize there were two large bommies at the site and the tender driver had dropped us on the other one.  After a little head scratching, I finally saw the second bommie, found my marker rock and the goby with the attached nudibranch! I got a few seconds of video then Burt Jones showed up and got a couple of shots before the goby freaked again and dived into its hole – we marveled at the  strength of the grip the nudibranch had on the goby fin.

Nudibranch on Goby Solomon Islands Ned DeLoach

Nudibranch preying on shrimp goby (Solomon Islands)

Nudibranch on goby Close-up Solomons Ned DeLoach

Close-up nudibranch preying on shrimp goby

In 2009, on a sandy slope in the Florida Islands in the Solomons, I saw another! I was scouting for Ned and by the time he got some photos, the goby decided I was a threat and dived into its hole. The nudibranch hung on during what was a very fast and certainly violent by nudibranch standards, dive by the goby into the burrow.

Bob Bolland’s Okinawa Slug Site has more photos and lists references, including the paper, The First Association of an Adult Mollusk (Nudibranchia: Doridae) and a Fish (Perciformes: Gobiidae) and the 2000,  paper  that confirms the nudibranch does feed on the goby fins – I think before that, the nature of the relationship was speculation. And the paper has a close-up of the hooked radula of the nudibranch’s mouth, which helps explain why the nudi is able to hang on the way it does. I’ve loaded a little bit of video on our BlennyWatcher YouTube channel  so you can see how the nudi hangs on when the goby bolts, or you can click below to watch.