I recently took a visitor to see the aquaria on display at the NOAA lab on Lena Point. This is not on my usual itinerary, but I become so captivated by one of the denizens in a tank that I decided to write about it anyway.
A small, strangely-shaped, yellowish organism was hopping along the rocks at the bottom of the tank, and upon closer inspection it turned out to be a fish–specifically a grunt sculpin, whose scientific name (Rhamphocottus richardsonii) is almost as long as the fish itself. I’d never heard of this little fish, so I did a little bit of digging to find out more. I then found out that it is a popular aquarium fish, and most of the observations of its behavior have no doubt been done in the artificial setting, and there seem to be few scientific studies, but nevertheless they are interesting fish, so here goes.
Grunt sculpins get their name for the sound they make, but what they are communicating is a mystery. They live on both sides of the North Pacific, in lower intertidal and subtidal waters down to about five hundred feet. They typically are less than four inches long, with a very big head on a body that dwindles rapidly down to a small tail. There are stout, blunt ridges on the front of the head, and the snout tapers down to a small mouth. The color varies: some are yellow, while others are cream-colored, orange, or brown, generally with dark streaking or mottling. (I have not been able to learn if an individual can change color, but it would not be very surprising if they do.) There is a vivid orange-red bar at the base of the tail. The orange-ish pectoral fins have little webbing on the lower half and are used for walking or hopping. (A hopping fish, yet!?).
When mating time comes, a female reportedly chivvies a male into a crevice or an empty giant barnacle shell, or some such shelter, and keeps him there until she lays her eggs (and presumably he fertilizes them). Or she may lay claim to a barnacle shell or bottle if it already holds a lurking male. A female can lay up to a hundred and fifty eggs, which are guarded in the nest shelter until hatching time. Males are said to do most of the nest-guarding, although females may take a turn. When it is time for the eggs to hatch, the guard-fish takes up the eggs in its mouth, swims out of the nest, and spits out the eggs into the water column. That action breaks the egg coverings and releases the larvae to join the zooplankton. The larvae have a ‘typical’ fish shape and later transform into the odd adult.
When I went back to the NOAA display, some days later, the little guy was nowhere to be seen, and I learned that they spend most of their time in hiding. Even though they have some body armor and small spines, they are feeble swimmers, and they have many predators. They often hide in giant barnacle shells, although they also use other hidey holes too. When one of these sculpins is well tucked into an empty barnacle shell, with only the front of the head in the opening, there is said to be a resemblance to a live barnacle with closed valves.
When one is lucky enough to find an empty big barnacle shell, it climbs in and points its head out the opening. When the surrounding live barnacles open up and start feeding, they orient toward the current, and so does the resident sculpin, pointing its head upstream. If the current reverses, as in a surge zone, the barnacles and the sculpin swing back and forth too, so the current brings food particles to the waiting consumers. Mandy Lindeberg at the NOAA lab offered the interesting idea that perhaps the sculpin mimics the barnacles, not only in motion, but also in coloration: the barnacles have orange tissues that are exposed when they open, and if the orange fins of the sculpin are near the opening of its lair, there is a visual similarity that might offer some protection from predators.
Their diet is chiefly little crustaceans, zooplankton, and fish larvae, which they catch in various ways. When ensconced in a sheltering barnacle, they slurp up small organisms that are swept by in the current. They also move around, slowly, to pick or suck up their prey from nooks and crannies. They can also catch prey in the open water, by slowly drifting up at an angle to unsuspecting victims and suddenly turning to the prey and sucking them in. In laboratory tests, they were quite successful in capturing little shrimp and crabs most of the time.
Thanks to Mandy Lindeberg and Rich Mattson for adding to the lore about this cool little fish.