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The Spotted ratfish (Hydrolagus colliei) is a cartilaginous fish belonging to the order Chimaeriformes, commonly known as chimaeras or ghost sharks. It is characterized by its distinctive appearance, including a large head, prominent eyes, a rabbit-like mouth, and a long, tapering tail resembling that of a rat. Its body is smooth and scaleless, typically bronze or silvery-gold with iridescent reflections, and covered in numerous white spots, which give it its common name. This species is a benthic inhabitant of temperate waters in the North Pacific.
Physical Characteristics
- Body shape
- elongated
- Coloration
- Iridescent bronze to silvery-gold or greenish-brown dorsally, fading to lighter ventral surfaces. Distinctive white spots are scattered across the body. Eyes are often emerald green.
- Scale type
- none
- Mouth position
- inferior
- Distinctive features
- Large, prominent, often emerald-green eyes, Rabbit-like mouth with plate-like teeth, Long, whip-like tail (heterocercal, but appearing rat-like), Smooth, scaleless skin, Venomous spine at the front of the first dorsal fin, Claspers in males (cephalic clasper on forehead, pelvic claspers)
- Dorsal fin
- Two dorsal fins. The first is tall and triangular, preceded by a sharp, venomous spine. The second dorsal fin is long and low, extending almost to the caudal fin.
- Tail fin
- Long, tapering, whip-like caudal fin, giving it a rat-like appearance. It is heterocercal but appears almost diphycercal.
- Pectoral fin
- Large, broad, and wing-like pectoral fins, used for propulsion and steering.
- Distinctive fins
- Pelvic fins are relatively small. Males possess a unique, club-shaped cephalic clasper on the forehead, in addition to the paired pelvic claspers.
Identification Tips
Coloration and Spots
Look for the iridescent bronze/silver body with numerous distinct white spots. This is the most defining visual characteristic.
Head and Mouth
Observe the large head, prominent emerald-green eyes, and small, rabbit-like mouth with plate-like teeth.
Dorsal Spine
Note the tall first dorsal fin preceded by a sharp, venomous spine. This is a key feature of chimaeras.
Tail
Identify the long, tapering, whip-like tail that gives it the 'ratfish' moniker.
Male Cephalic Clasper
In males, a unique, club-shaped clasper is present on the forehead, which is used to grasp the female during mating.
Habitat
- Water type
- saltwater
- Depth
- Typically found in depths ranging from 0 to 900 meters (0 to 2,950 feet), most commonly between 50 and 400 meters (160 to 1,300 feet).
- Environment
- Benthic or near-benthic on soft substrates (mud, sand) and rocky bottoms of continental shelves and slopes. Prefers cold, temperate waters.
- Geographic range
- Eastern North Pacific Ocean, from southeastern Alaska to Baja California, Mexico. Also found in the Bering Sea.
Aquarium Information
- Care level: expert
- Temperament: peaceful
- Diet: carnivore
- Minimum tank size: Not suitable for home aquaria; requires specialized public aquarium facilities.
- Temperature: 8-12°C (46-54°F)
- pH level: 7.8-8.4
- Hardness: High (marine salinity)
- Compatibility: Generally solitary; can be housed with other deep-water, non-aggressive species in very large, specialized exhibits.
- Special requirements: Requires very large, deep, cold-water aquaria with specialized filtration and lighting to mimic deep-sea conditions. Extremely sensitive to changes in water quality and temperature. Not recommended for private aquarists.
Wild Information
- Conservation status: least concern
- Seasonality: Present year-round within its range, though movements may be influenced by prey availability and reproductive cycles.
- Market price: Low to none
- Commercial importance: none
- Taste: Reported to have a mild, somewhat oily flavor, but not commonly consumed.
- Texture: Soft, flaky.
- Cooking methods: Not typically prepared for consumption due to low commercial value and potential for strong ammonia odor if not handled properly.
- Nutritional value: Limited information available due to lack of consumption. Likely contains omega-3 fatty acids like other cartilaginous fish.
Key Facts
Ancient Lineageevolution
Chimaeras, including the Spotted ratfish, are often referred to as 'ghost sharks' due to their deep-sea habitat and their evolutionary lineage, which diverged from sharks and rays approximately 400 million years ago, making them one of the oldest groups of fish.
Unique Reproductionbehavior
Spotted ratfish lay distinctive spindle-shaped egg cases, often referred to as 'mermaid's purses,' which are anchored to the seabed. These cases can be quite large, up to 10-12 cm long, and protect the developing embryo for an extended period (up to a year).
Electroreceptionbehavior
Like sharks and rays, chimaeras possess electroreceptors (ampullae of Lorenzini) on their snouts, which allow them to detect the weak electrical fields generated by prey, aiding in hunting in low-light deep-sea environments.
Male Claspersamazing
Male Spotted ratfish have a unique, retractable, club-shaped clasper on their forehead, in addition to the paired pelvic claspers. This cephalic clasper is used to hold the female during mating, ensuring successful fertilization.
Safety Information
Venomous- Safety level: venomous
- Venomous: Yes
- Edibility: not recommended
- Handling notes: The Spotted ratfish possesses a sharp, venomous spine at the leading edge of its first dorsal fin. This spine can inflict a painful wound, and the venom can cause swelling, redness, and intense pain. Handle with extreme caution, avoiding direct contact with the dorsal spine. If stung, seek medical attention, as the venom can cause systemic effects in sensitive individuals. Anglers should be aware of this hazard when catching and releasing.
Similar Species
Longnose Chimaera
Harriotta raleighana
Possesses a very long, pointed snout, unlike the blunt snout of the Spotted ratfish. Lacks the distinct white spots.
Pacific Black Ghostshark
Hydrolagus melanophasma
Generally darker in coloration (black to dark brown) and lacks the prominent white spots. Found in deeper waters.
Bigeye Chimaera
Hydrolagus mirabilis
Has exceptionally large eyes and a more uniformly dark coloration, lacking the distinct white spots. Found in the Atlantic.
Scientific Classification
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Chondrichthyes
- Order
- Chimaeriformes
- Family
- Chimaeridae
- Genus
- Hydrolagus
- Species
- colliei
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