Rock prickleback (Xiphister mucosus)
This fish is not an eel, but it certainly has an eel-like appearance. It resides in rocky habitats that are exposed to moderate wave action, where it can be found under rocks and algae at low tide. It is characterized by the greenish-black body color with faint white markings around the base of the tail and white strips below the eyes (not seen in this top view).
The long dorsal fin starts right behind the head, unlike its cousin the Black Prickleback, whose dorsal fin arises further back on the body. This 9-inch specimen is half of the size of a full-grown individual, which can reach 23 inches.
The pricklebacks are a family of fish characterized by long, slender, compressed bodies. The dorsal fin goes the length of the body, merging with the caudal fin. The pectoral fins, near the gill covers, are very small to absent. They are called pricklebacks because the dorsal fin is mostly composed of hard, spiny rays with sharp tips (rays are supports of the fleshy fin). There are about 20 species in the Northwest, many of which live in the subtidal zone and are seen only by divers.
The rock prickleback ranges from southeast Alaska to southern California. It is unique in that it seems to eat a high percentage of algae along with feeding on small animals. It lays its eggs under rocks and vegetation, where the male coils around them for protection.
David W. Jamison is a marine biologist and Boston Harbor resident.