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Aquarium of the Pacific - Online Learning Center - Species Print Sheet

Conservation Status:  Safe for Now

Climate Change:  Uncertain

Aquatic SpeciesSpotted Ratfish

Hydrolagus colliei

Spotted ratfish on Seafloor Spotted ratfish are found near the sea floor where there are mud and rocky bottoms at depths of intertidal to 900 m (2970 ft) | Courtesy of NOAA
Spotted ratfish on Seafloor - popup
Spotted ratfish are found near the sea floor where there are mud and rocky bottoms at depths of intertidal to 900 m (2970 ft) Courtesy of NOAA

Species In-Depth | Print full entry

At the Aquarium

The habitat for our spotted ratfish is the Whale Fall Exhibit in the Wonders of the Deep Gallery where it lives with the Pacific hagfish.

Geographic Distribution

Eastern Pacific Ocean from the panhandle of Alaska south to Baja California. Concentrated between British Columbia and southern California.


Spotted ratfish are found near the sea floor where there are mud and rocky bottoms at depths of intertidal to 900 m (2970 ft). Preferring water temperatures of 7-9 Co (45 to 48 o F), as the distribution moves southward into warmer water, these fish descend to progressively deeper depths where the water is colder. They tend to move closer to shallow water during the spring and autumn, then to deeper water in summer and winter.

Physical Characteristics

Spotted ratfish have a rabbit-like head, a protruding snout, and a body that tapers toward the narrow tail that is almost half the overall length of the fish. Their skin is smooth and scaleless. Triangular pectoral fins are large and well-developed. There are large spines in front of the dorsal fin. These fish have one pair of teeth in the lower jaw and two pairs in the upper. Male spotted ratfish have spines located on their head and two pairs of claspers next to the pelvic fin base.

Spotted ratfish are brown or gray with hues of gold, green, and blue. They have white spots. Their eyes are green.


Total length: To 60 cm (23.6 in)
Body length: to 36 cm (14.2 in)


These fish mainly use electroreception and smell to locate prey. Because they are feeble swimmers, their prey must be fairly still with limited abilities to escape. They swim slowly near the seafloor bottom in search of clams, crabs, shrimps, polychaete worms, and small benthic fishes. They are also known to be cannibals, eating their own egg cases as well as other free-swimming ratfish.


Males reach maturity when their body length is 18.5 to 20 cm (7.3 to 7.9 in). Females reach maturity at 24 to 25 cm (9.4 to 9.8 in) body length. Breeding is seasonal, taking place in the autumn and spring with complicated courtship displays, such as color change in males and distinct movements by both sexes. Fertilization is internal and females are oviparous. A female’s fertile period lasts several months. During this time she expels pairs of fertilized spoon-shaped, leathery egg cases into muddy areas every 10 to 14 days. It can take 19 to 30 hours for the female to expel the egg case.

The cases first hang in the water, suspended from the female by the elastic capsular filament. In four to six days the egg cases fall to the seafloor where they incubate for about 12 months. Newborn ratfish are about 14 cm (5.5 in) long and resemble an adult ratfish. They grow to a length of 30 cm (1 ft) in their first year.


Using their pectoral fins, spotted ratfish swim slowly in search of prey they find primarily by smell. At sundown they migrate from deep to shallower waters on the prowl for a meal. They tend to form groups based on age and sex.


The spotted ratfish is a chimera, a group of fish believed to have evolved from sharks 400 million years ago. Chimaeras resemble sharks in that they use claspers for internal fertilization of females and they lay eggs with leathery cases. Unlike sharks, male chimaeras also have retractable sexual appendages on the forehead and in front of the pelvic fins. Also their upper jaws are fused with their skulls and they have separate anal and urogenital openings. They do not have any sharp and replaceable teeth like sharks have; instead, they have just three pairs of large permanent grinding tooth plates. Like bony fishes, they have gill covers. They retain traces of a third pair of limbs, the only vertebrates that do so.


There are no conservation methods being developed for the spotted ratfish except in Oregon where trawlers are using special gear to avoid the fish in their bycatch. Predators include soupfin sharks, dogfish sharks, Pacific halibut, and Pigeon Guillemots.

Special Notes

Male spotted ratfish have an appendage called a tenaculum on their forehead that is used during courtship to secure the female by the hollow in the back of her head.