''Chimaera monstrosa'', also known as the rabbit fish or rat fish, is a northeast

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

and

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

species of

cartilaginous fish Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue ...

in the family

Chimaeridae The Chimaeridae, or short-nosed chimaeras, are a family of cartilaginous fish. They resemble other chimaeras in general form and habits, but have short, rounded snouts, without the modifications found in related families. Many species have lon ...

. The rabbit fish is known for its characteristically large head and small, tapering body. With large eyes, nostrils, and tooth plates, the head gives them a rabbit-like appearance, hence the nickname “Rabbit fish”. They can grow to and live for up to 30 years.

Description

The appearance of ''C. monstrosa'' shares characteristics of its distant relatives,

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...

s. It characteristically has a large head and a tapering body that ends in its whip-like tail, and has a short snout with an overhanging mouth. The top

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

is positioned high on the spine of the fish, and is triangular and tall in height. Positioned in the mid-section of the fish, the spine runs throughout the length of the fish and continuously joins with the upper part of the

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

; this dorsal spine is also mildly poisonous and can cause painful stings. One distinguishing feature of the fish, compared to its close relatives, is the

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

, which is distinctly separated from lancet-shaped caudal fin. The color is silver-green with spots of brown. Additionally, they have marmor-white stripes in all directions with a distinct

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

can be seen clearly on the head. The rabbit fish can grow up to long, and weigh . More specifically, this chimaera species is characterized by a slow-growth rate, and a long life expectancy. In the study of one

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...

, the theoretical asymptotic length of this fish was estimated at 78.87 cm with a yearly growth rate of 6.73% per year. With these estimates of growth, the study also suggests the maximum ages of the fish to be 30 years for males and 26 for females, with the maturity age of the sample being 13.4 years for males and 11.2 years for females.

Distribution and habitat

The geographic habitat of the fish has been registered around the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

and the Eastern parts of the Atlantic Ocean. This geographic range starts northwards Morocco and extends to the northern areas of Norway and Iceland in the Northern North Sea. Within these geological areas, the depth range of ''C. monstrosa'' is , but it is most abundant in upper to middle continental slope habitats at depths of . Within these parameters, the water temperatures of the species habitats are most commonly in the range . There have been reports of summer inshore migration of ''C. monstrosa'' to lay eggs in depths as low as .

Diet

''Chimaera monstrosa'' is classified as a

benthophagous Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.opportunistic feeders Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffixes -vore, -vory, or -vorous from Latin ''vorare'', meaning "to devour", or -phage, -phagy, or -phagous from Greek φαγ ...

. Comparing the digestive tracts of individuals with varying body sizes, a study found that the diet of the species was widely diverse in relation to size. Specimens smaller than mainly fed on

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...

, while those with lengths between fed on both amphipods and

decapods The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is estim ...

. Larger individuals (more than ) had a narrow diet spectrum, consuming mainly decapods. Conditioned by predator size group, significant differences in diet were observed between geographical areas and depths. This suggests that despite some degree of prey specialization according to predator size, this deep-water species can change its diet in accordance with the food-restricted environment that characterizes its habitat.

Reproduction

''Chimaera monstrosa'' are fish that have distinct sex from birth. They reproduce by internal fertilization of male and female. For reproduction, ''C. monstrosa'' displays a small club like structure with a bulbous tip armed with numerous sharp denticles located on the top of the head. This structure is suggested to be used by male fish to grasp the pectoral fin of the female during copulation. The species is also

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

, meaning that the embryo development happens in eggs, and not in the female. Specifically, the reproductive tendencies of the ''Chimaera monstrosa'' show sexual segregation in different depths of water, with the females living at lower depths. This segregation of the sexes is attributed to two main factors: the regulation of sperm in males in warmer and shallower waters, and less aggression of sex. For males, they live in water to regulate sperm. For the females, they prefer deeper waters of , but go up to depths of to mate with males. After mating, they migrate inshore to lay eggs in the spring of summer.

Conservation

According to the IUCN Red List, ''Chimaera monstrosa'' is categorized as vulnerable. Due to its high levels of lipids, the species has gained interest in fisheries for its liver oils to manufacture dietary supplements. Aside from its values for oil, the ''C. monstrosa'' is mainly discarded as bycatch product in fishing.

Description

Distribution and habitat

Diet

Reproduction

Conservation

References

Further reading