Spotted Ratfish

Spotted Ratfish, Hydrolagus colliei

The Spotted Ratfish, Hydrolagus colliei, whose common Spanish name is quimera manchada, is a species in the Shortnose Chimaera or Chimaeridae Family, known collectively as quimeras in Mexico. This fish received its common name from its pointed rat-like tail and is also known as the Spotted Ghost Shark. Globally, there are forty-eight members of the family placed in three genera, and only five species in the genus Hydrolagus, four of which are found in Mexican waters, all in the Pacific.

The Spotted Ratfish have compressed bodies that are unusual in that the body length is elongated between the gills and the upper caudal fin lobe and tapers to a filamentous tail. They are gray or brown with hues of gold, green, and blue that transition to silver ventrally. They are covered with white spots; the spots on their head and upper body are small and those on their lower body and tail are larger and more elongated. Their fins are gray. In addition, their upper caudal and dorsal fins have white bases and their lower caudal fin lobe is white. Their head is very large and “rabbit-like” with a short rounded conical duckbill-shaped snout, large emerald green eyes, and large nostrils. Their mouth is small and on the underside with two pairs of plates on the top jaw and one pair on the bottom jaw. Males have a spiny club-shaped process on their head and sharp retracting claspers behind their pelvic fins. They have no anal fin. Their caudal fin is elongated being almost half the overall length of the fish with two equally-sized lobes and a long pointed whip-like filament. They have two dorsal fins, the first being large, triangular, and erect with a long venomous spine at the front; the second being low with a long base and an indentation in the middle. Their pectoral and pelvic fins are broad and triangular. They have a well-developed lateral line and smooth skin without scales.

The Spotted Ratfish are primarily a deep-water species found near the bottom in and around rocky areas and over muddy bottoms but they also occur at shallower depths in the northern part of their range where they are also more abundant. They are found between the surface and depths of 4,070 feet; they are located in shallower waters during the spring and fall and in deeper waters in summer and winter. They prefer water temperatures between 7oC (45oF) and 9oC (48oF). They reach a maximum length of 1.0 meter (3 feet 3 inches) with females being much larger than males. They are poor swimmers and move via a series of barrel rolls and corkscrew turns. They are nighttime predators and locate their prey primarily though electroreception and smell. They consume crabs, shrimps, polychaetes worms, and small benthic fish. In turn they are preyed upon by Giant Sea Bass, Lingcod, Pacific Halibut, rockfish, sharks, marine mammals, and sea birds. Reproduction is oviparous with spawning during the summer months. Each female releases up to two fertilized eggs contained in spoon-shaped cases every ten to 14 days for several months (between twenty and twenty-nine eggs per year) into sandy or muddy bottoms. The egg cases are leather-like, five inches long, and have a filament that is used to attach them to the ocean floor. Development of the eggs can take up to a year. The newborns are about 14 cm (5.5 inches) in length and will double in size in the first year.

In Mexican waters the Spotted Ratfish are found along the entire west coast of Baja. There are two isolated populations in the Sea of Cortez, one around Isla Tiburon, and the other in the Bahiá de La Paz to Cabo San Lucas region.

The Spotted Ratfish is most likely confused with the Eastern Pacific Black Ghostshark, Hydrolagus melanophasma (larger; darker colored; without spots).

The Spotted Ratfish are not a targeted species. They are taken as a by-catch in commercial trawl and longline fisheries and to a lesser extent by recreational anglers. They are viewed as trash fish and rarely retained. They are not considered dangerous to humans but they have a venomous dorsal spine that can inflict painful wounds. Males also have sharp clasping organs. They are encountered at night by divers and will try to avoid them unless provoked. They can be found on a very limited basis in some public aquariums but are not popular due to their requirements for low light and cold water. From a conservation perspective they are currently considered of Least Concern being abundant over a wide range on the shelf and upper continental slope.

Spotted Ratfish, Hydrolagus colliei. Fish provided by the commercial fishermen of Bahía Kino, Sonora, March 2015. Length: 51 cm (20 inches). Photo and identification courtesy of Maria Johnson, Prescott College Kino Bay Center, Kino Bay, Sonora.