Rhamphocottus richardsonii Günther, 1874

Common Name and Size

Rhamphocottus richardsonii, commonly known as the grunt sculpin, reaches a maximum recorded total length of 8.9 cm.

Body and Fin Morphology

This species has a large head, short stout body, elongated pig-like snout, and orange fins. Its body is typically yellow with brown stripes, and its pectoral fins are a particularly vivid orange.

Mouth and Snout Trait

Compared to other sculpins, it has a small mouth paired with a longer snout, which affects its feeding habits.

Locomotion

While it is capable of swimming in an unusual upright posture with its head pointing upward, it mostly moves by "hopping" along the ocean floor using its pectoral fins.

Distinguishing Phenotypic Traits

It can be distinguished phenotypically by several key traits: its pectoral fins are separated from the upper lobe, it retains both anal and dorsal fins, and its hypural-parhypural bone is formed as a single solid piece.

Geographic Distribution

The grunt sculpin is distributed along coasts of the eastern Pacific Ocean, ranging from southern California north to the Bering Sea; it has also been observed off the coast of Japan.

Habitat Types

Within this range, it occupies a diverse set of habitats including rocky shores, kelp forests, sandy beaches, and reefs.

Depth Range

It is most commonly found in shallow water as little as two meters deep, but has been recorded at depths up to 165 meters.

Shelter Preference

It prefers to shelter inside empty giant barnacles, and will instead inhabit debris under piers and floats when giant barnacles are not available.

Barnacle Mimicry Behavior

When sheltering inside barnacles, it extends its fins and waves them to mimic the appearance and movement of the feeding cirri of a living barnacle.

Spawning Period and Location

Spawning for grunt sculpins takes place on rocky shores between August and October.

Reproductive Behavior

Females are the dominant partner during reproduction; they chase and trap males within rocky crevices until they have laid their full clutch of approximately 150 eggs.

Egg Hatching

Eggs hatch between 16 and 20 weeks after fertilization, with the exact timing depending on water temperature.

Larval Occurrence Period

Larval grunt sculpins have been recorded between March and June.

Larval Survival Requirements

Larvae must stay close to shore to survive, as any larvae carried out into the open ocean by planktonic dispersal are very unlikely to survive.

Larval Behavior Uncertainties

It remains unclear how larvae are adapted to remain near shore, or what environmental factors influence this behavior.