Latin name

Chimaera monstrosa

Other name

Rat fish

Identification

The head of the rabbit fish is thick with a rounded snout. The eyes are large. The mouth is lower, small and transverse. The upper jaw has 4 and the lower jaw has 2 large beak-shaped tooth plates. The body is elongated, thinning strongly behind. The narrow bicoid tail ends in a long filament. There is a system of sensory canals on the head. The skin is bare and soft, occasionally covered with rudimentary spines. Males have a thin bony projection between the eyes that curves forward.

Features of fish fins

The pectoral fins of this fish are very large. The first dorsal fin is high and short, with a strong, long spike on the leading edge; the second dorsal fin has a low edge that extends to the beginning of the caudal fin. The anal fin is small.

Fish colouring

The coloration of the dorsal surface of the rabbit fish is dark brown with a reddish tinge, the sides are covered with spots, the ventral side is bright. The caudal, anal, and posterior parts of the second dorsal fins have a blackish-brown edge. The skin of males is smooth and shows a variety of colors.

Distribution

This species is widespread in the North Atlantic and adjacent seas of the Arctic Ocean. It is found off the coasts of Norway, Iceland, Ireland, the United Kingdom, France, Italy, Portugal, Morocco, the Azores and Madeira, and the Mediterranean Sea.

Habitat

This marine, bathydemersal, oceanodromous fish is found at depths from 40 to 1400 m. In the north it is most often found at depths of 200-500 m, and in the south at 350-700 m. In the winter it moves closer to the coast. At this time it is caught in Norwegian fjords at depths of 90-180 m.

Size

Adult chimeras reach a length of 1.5 m and a maximum recorded mass of 2.5 kg. Juveniles are 11 cm long. Males are generally smaller than females.

Behavior

Juvenile rabbit fish are rarely caught. It is known to be caught off the Faroe Islands at a depth of 1000m and off Ireland at a depth of 600m.

Food and feeding habits

Bentophagous. Their diet consists mainly of invertebrates: crustaceans, mollusks, worms and echinoderms. Fish are sometimes found in their stomachs.

Reproduction

This species lays eggs enclosed in a horn capsule. Reproduction occurs throughout the year. Up to 200 eggs develop in the ovaries of the female. The female lays two eggs each several times without re-fertilization. Before laying, the female carries the eggs attached to the oviducts. She then deposits them on the seabed at relatively deep depths, sometimes up to 400 meters. The yolk is 26 mm in diameter. The capsule has a fin-like edge up to 4 mm high. The lower end of the capsule is cylindrical, the upper end has the appearance of a narrow thread-like appendage that serves to attach the egg. The capsule is 163-77 mm long and about 25 mm wide. The length of the appendage is 30-40 mm. The capsule is shiny brown to olive green. Eggs develop for about a year. Newborns hatch fully formed.

Fishing

The rabbit fish is not a commercial fish, but there are cases of it being caught intentionally. It is often caught as by-catch in bottom trawls when fishing for other fish.

Relationship with a person

Traumatogenic. The flesh of this fish is tough, but it is eaten in some countries.

Interesting facts

Although many species of chimaeras have gone extinct, the rabbit fish is a representative of the subclass Holocephali, an evolutionary branch that diverged from sharks and rays about 420 million years ago. While its extinct relatives were more diverse, modern chimaeras, including C. monstrosa, represent a compact but surviving group that has existed for at least 220 million years. The main secret of its survival is specialization for life at great depths. It has electroreceptors (ampullae of Lorenzini) — about 700 pores on its head that help detect weak electrical signals from prey in conditions of eternal darkness. It also has a well-developed sense of smell and a flexible neck that helps it precisely aim at prey. It feeds on benthic invertebrates such as mollusks, and its teeth have transformed into beak-like plates, perfectly suited for cracking hard shells. It does not even have a proper stomach, which simplifies digestion. Thus, the rabbit fish is not just a randomly surviving species, but a product of long and narrow evolutionary specialization that allowed it to occupy and maintain its ecological niche in the depths of the ocean.