Grunt Sculpin
Rhamphocottus richardsonii
There are a long list of bottom dwelling, strangely shaped fish in the Northeast Pacific. In days long past when these species were all given names, scientists rather lazily labelled nearly anything that rests on the seafloor a sculpin. As research progresses, many former-sculpins now belong to their own unique groupings, including the Sea ravens, toadfishes, and of course, the Grunt sculpin.
June 2018: A Grunt sculpin presents itself in full view while patrolling its exhibit at the Discovery Passage Aquarium in Campbell River, B.C. This is the first Grunt sculpin I had the pleasure of working with as an aquarist.
📖 Description 📖
The Grunt sculpin is a small but charismatic fish cherished by scuba divers, naturalists, and aquarists across the Pacific. They do not swim like most fish, but instead use their reinforced pectoral fins to ‘hop’ along the seafloor. When threatened (or threatening others) they can however swim at impressive speeds across short distances, but quickly settle down to the seafloor afterwards. In this sense, they are very similar to chickens, who can only fly short distances.
February 2020: A brightly coloured Grunt sculpin braves the sand flats under cover of darkness in search of prey.
Grunt sculpins are not slimy or scaly, but instead they are very stony and rough in texture. As you may deduce from their impressive colouration, this species relies heavily on camoflage. Having a ridgid, mishapen body makes it that much more difficult to be swallowed by birds or large fishes when they do get spotted.
🌎 Distribution 🌎
Grunt sculpins are encountered from Southern California all the way through to the Aleutian Islands. There appears to be a break in their distribution in Southeast Alaska, however this may be due to the lack of survey data. Their distribution is nearly identical to that of the Giant acorn barnacle, a species whose shells are important for shelter and laying eggs.
For many years, this species was thought to be the sole member of it’s famiy (Rhamphocottidae). In recent years, several new species have been discovered and classified, including a species that is nearly identical in japan, known as Rhamphocottus nagaakii [1].
Distribution of the Grunt sculpin, Rhamphocottus richardsonii. Suitable habitat depicted in red.
Several other members of family Rhamphocottidae are found in the deep sea, including Marukawichthys ambulator and Ereunias grallator. These bizarre species can only be described as a “deep-sea versions of the Grunt sculpin”.
🏝 Habitat 🏝
A discussion on the habitats of this fish is not complete without discussing its relationship with the Giant acorn barnacle. The shape, size, and colour of the Grunt sculpin are perfect for fitting inside of empty barnacle shells and mimicking the colours of one that is still alive. This camouflage protects them from predators that eat fishes but have no interest in barnacles.
As divers explore more and more of our local waters, the list of habitats that the Grunt sculpin is known to occupy has only grown. Despite their very close relationship with Giant acorn barnacles, they are rather often found in regions and habitats with no such barnacles in sight. These fish seem to also have knowledge of taking advantage of other types of shells, including Purple-hinged rock scallops and the remains of Red sea urchins.
Depth of suitable habitat for the Grunt sculpin, Rhamphocottus richardsonii. Suitable habitat depicted in red. Not to scale.
Interestingly, this fish is only found in relatively shallow waters. Many of the shells that the Grunt sculpin will live inside of are those of filter feeders, who feed on plankton that require the sun to grow. Naturally, species that rely on plankton for survival are only encountered close to the surface.
January 2021: A Grunt sculpin occupies a rather large shell of a Giant acorn barnacle. Photographed in Deep Cove on Southern Vancouver Island.
🦐 Diet 🦐
Some people refer to the Grunt sculpin as a “Northern seahorse” due to its long, pointed snout. This visual similarity is actually due to the preferred prey of these two very different fishes. Both feed only on very small animals, including amphipods, copepods, other small crustaceans, polychaetes, and small fishes [2].
When hunting, a Grunt sculpin hops along the seafloor, closely watching for prey in between cracks in the rock, or peering up through sand or mud.
🐙 Life Cycle 🐙
Predictably, the Giant acorn barnacle is also central to the Grunt sculpin’s lifecycle. During mating season, which is currently understood to be between the months of November and March, females will track down a male of their choosing and essentially chase them into an empty barnacle shell or similar structure.
The mother then lays her eggs and the father fertilizes them. The mother then leaves the father to care for and guard over the eggs for the next several months until they hatch.
It is currently believed that Grunt sculpins can survive for as many as 7 years in the wild, however such data is very challenging to verify [2].
March 2023: A lone Grunt sculpin peers out from the safety of its barnacle shell.
📚 References 📚
[1] Hiroyuki, M. et al. (2023). Rhamphocottus nagaakii (Cottoidea: Rhamphocottidae), a new species of grunt sculpin from the northwestern Pacific, with notes on the phylogeography of the genus Rhamphocottus. Ichthyological Research, 70(2): pp. 268-285. https://ui.adsabs.harvard.edu/link_gateway/2023IchtR..70..268M/doi:10.1007/s10228-022-00885-y
[2] Aquarium of the Pacific. (n.d.). Grunt sculpin. Retrieved March 5th, 2025, from https://www.aquariumofpacific.org/onlinelearningcenter/species/grunt_sculpin
