This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Behold the sea robin: a fish with a front end of an exotic race car who treads upon the sand with the daintiest little chicken legs ever.
What a charmer! One almost feels like the fish needs a dapper top hat and cane. This footage was taken by Deep Discoverer, the ROV of the NOAA Ship Okeanos Explorer, which I toured and wrote about recently here, in the waters off American Samoa last week. They are cruising the poorly explored waters around Samoa and American Samoa through April. Check out the live stream of their explorations any time you get a chance.
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The sea robin, also called gurnard for the croaking noises it makes when hauled up by a fisherman, is a delightfully odd creature. To wit: the croaking noise comes from the unusual ability of this fish to beat its swim bladder with a special muscle, presumably something like a tympani.
Those “legs” aren’t actually legs, but instead fin rays that have evolved into tentacle-like digits, separate from rest of the pectoral fin. In the process, the normally rigid rays somehow acquired the ability to flex and bend in ways normal fin rays cannot. It looks for all the world like this fish is strolling across the seafloor. But it is not. Or at least, in spite of the title of this post, those legs aren’t actually made for walking.
Sea robins inhabit essentially the same niche as a catfish, but do so in the ocean instead of a muddy river bottom. Instead of a catfish’s whiskers, the sea robin has a crazy pair of chin barbels that bear a striking resemblance to a predatory harp sponge. The “legs”, along with the barbels, are probably serving the same function: prey detection. The legs have sensors that detect chemicals commonly emitted by the invertebrates buried in the sand that they prey on. Sea robins will eat pretty much anything they can get their mouths on, including, according to one source, shrimp, crabs, amphipods, squid, bivalve mollusks, annelid worms, small fish, and even seaweed. So what looks to us like walking is in fact more like groping through the refrigerator, looking for something good to eat.