• Source: Rabbit fish

Chimaera monstrosa, also known as the rabbit fish or rat fish, is a northeast Atlantic and Mediterranean species of cartilaginous fish in the family Chimaeridae. 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 1.5 metres (5 ft) and live for up to 30 years.




Description



The appearance of C. monstrosa shares characteristics of its distant relatives, sharks. 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 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; 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, 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 can be seen clearly on the head.
The rabbit fish can grow up to 1.5 m (5 ft) long, and weigh 2.5 kg (5.5 lb). More specifically, this chimaera species is characterized by a slow-growth rate, and a long life expectancy. In the study of one population, 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 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 50 to 1,000 metres (160 to 3,280 ft), but it is most abundant in
upper to middle continental slope habitats at depths of 300 to 500 metres (980 to 1,640 ft). Within these parameters, the water temperatures of the species habitats are most commonly in the range 4.7–8.0 °C (40.5–46.4 °F). There have been reports of summer inshore migration of C. monstrosa to lay eggs in depths as low as 100 m (330 ft).




Diet


Chimaera monstrosa is classified as a benthophagous species. This means that its main diet comprises bottom-feeding invertebrates. This includes animals such as crabs, molluscs, octopuses, sea-worms, and sea urchins. However, studies have also shown that C. monstrosa are opportunistic feeders. 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 22 cm (9 inches) mainly fed on amphipods, while those with lengths between 22 and 46 cm (9 and 18 inches) fed on both amphipods and decapods. Larger individuals (more than 46 cm or 18 inches) 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, 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 500–600 m (1,600–2,000 ft) to regulate sperm. For the females, they prefer deeper waters of 800 m (2,600 ft), but go up to depths of 500–600 m (1,600–2,000 ft) 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 value for oil, the C. monstrosa is mainly discarded as bycatch in fishing.




References






Further reading



FAO Aquatic Species Distribution Map of Chimaera monstrosa
• Source: Rabbitfish

Rabbitfishes or spinefoots, genus Siganus, are perciform fishes in the family Siganidae. It is the only extant genus in its family and has 29 species. In some now obsolete classifications, the species having prominent face stripes—colloquially called foxfaces–are in the genus Lo. Other species, such as the masked spinefoot (S. puellus), show a reduced form of the stripe pattern. Rabbitfishes are native to shallow waters in the Indo-Pacific, but S. luridus and S. rivulatus have become established in the eastern Mediterranean via Lessepsian migration. They are commercially important food fish, and can be used in the preparation of dishes such as bagoong.




Taxonomy


The genus Siganus was described in 1775 by the Danish zoologist Johan Christian Fabricius with Siganus rivulatus, a species also described by Fabricius in 1775, designated as the type species. The description was based on notes taken by the naturalist Peter Forsskål when he was on the Danish Arabia expedition (1761–67) and was published in Carsten Niebuhr's Descriptiones animalium avium, amphibiorum, piscium, insectorum, vermium; quae in itinere orientali observavit Petrus Forskål. Post mortem auctoris edidit Carsten Niebuhr. Catalog of Fishes lists the authority as " Fabricius [J. C.] (ex Forsskål) in Niebuhr 1775" and states that the genus is valid as "Siganus Fabricius 1775".
Carl Linnaeus originally described the genus Teuthis, with the type species being Teuthis hepatus. One of the type specimens he used looks like Siganus javus, although the other is definitely not a rabbitfish, and the International Commission on Zoological Nomenclature has been asked to suppress the name Teuthis in favour of Siganus to reflect the prevailing usage.
The name Siganus is a latinisation of the local Arabic name for the marbled rabbitfish (S. rivulatus) in Yemen, Sidjan which can also be written as Sigian, and means "rabbitfish".

In 2007 Kurriwa et al., outlined a way to split the genus—if the scientific community so desires:

An ancient group containing e.g. S. woodlandi
Another fairly small group containing, e.g., the S. canaliculatus/S. fuscescens) complex
The remainder of Siganus, including the foxfaces
Other lineages might exist and make obsolete the somewhat weak distinction between the second and third groups. Also, it is not known where the type species S. rivulatus would fall, hence names for these three subgenera or genera are not established at present.
Hybridizaton has played a role in the evolution of the Siganidae, as evidenced by comparison of mtDNA cytochrome b and nDNA internal transcribed spacer 1 sequence data. Evidence exists of interbreeding between S. guttatus and S. lineatus, as well as between S. doliatus and S. virgatus.
Also, either females of the last common ancestor of S. puellus and the S. punctatus interbred with females ancestral to the main non-foxface lineage, or males of the former hybridized with females of the last common ancestor of S. punctatissimus and the foxfaces, while males of the latter mated with females of the original foxface species.
An individual was found that looked like a slightly aberrant blue-spotted spinefoot (S. corallinus). On investigation, it turned out to be an offspring of a hybrid between a female of that species and a male masked spinefoot, which had successfully backcrossed with the blue-spotted spinefoot.




= Species

=
As noted above, several presumed species are suspected to actively interbreed even today; these might warrant merging as a single species. This applies to the white-spotted spinefoot (S. canaliculatus) and the mottled spinefoot (S. fuscescens), and to the blotched foxface (S. unimaculatus) and the foxface rabbitfish (S. vulpinus). Alternatively they might be very recently evolved species that have not yet undergone complete lineage sorting, but their biogeography suggests that each group is just color morphs of a single species. On the other hand, the morphologically diverse blue-spotted spinefoot (S. corallinus) might represent more than one species; orange individuals are found at the north of its range, while yellow ones occur to the south, and these two may be completely parapatric.

There are currently 29 recognized species in this genus:

Siganus argenteus (Quoy & Gaimard, 1825) (Streamlined spinefoot)
Siganus canaliculatus (M. Park, 1797) (White-spotted spinefoot)
Siganus corallinus (Valenciennes, 1835) (Blue-spotted spinefoot)
Siganus doliatus Guérin-Méneville, 1829 (Barred spinefoot)
Siganus fuscescens (Houttuyn, 1782) (Mottled spinefoot)
Siganus guttatus (Bloch, 1787) (Goldlined spinefoot)
Siganus insomnis Woodland & R. C. Anderson, 2014 (Bronze-lined rabbitfish)
Siganus javus (Linnaeus, 1766) (Streaked spinefoot)
Siganus labyrinthodes (Bleeker, 1853) (Labyrinth spinefoot)
Siganus lineatus (Valenciennes, 1835) (Golden-lined spinefoot)
Siganus luridus (Rüppell, 1829) (Dusky spinefoot)
Siganus magnificus (G. H. Burgess, 1977) (Magnificent rabbitfish)
Siganus niger Woodland, 1990 (Black foxface)
Siganus puelloides Woodland & Randall, 1979 (Blackeye rabbitfish)
Siganus puellus (Schlegel, 1852) (Masked spinefoot)
Siganus punctatissimus Fowler & B. A. Bean, 1929 (Peppered spinefoot)
Siganus punctatus (Schneider & Forster, 1801) (Goldspotted spinefoot)
Siganus randalli Woodland, 1990 (Variegated spinefoot)
Siganus rivulatus Forsskål & Niebuhr, 1775 (Marbled spinefoot)
Siganus spinus (Linnaeus, 1758) (Little spinefoot)
Siganus stellatus (Forsskål, 1775) (Brown-spotted spinefoot)
Siganus sutor (Valenciennes, 1835) (Shoemaker spinefoot)
Siganus trispilos Woodland & G. R. Allen, 1977 (Threeblotched rabbitfish)
Siganus unimaculatus (Evermann & Seale, 1907) (Blotched foxface)
Siganus uspi Gawel & Woodland, 1974 (Bicolored foxface)
Siganus vermiculatus (Valenciennes, 1835) (Vermiculated spinefoot)
Siganus virgatus (Valenciennes, 1835) (Barhead spinefoot)
Siganus vulpinus (Schlegel & J. P. Müller, 1845) (Foxface)
Siganus woodlandi Randall & Kulbicki, 2005




Characteristics


Rabbitfishes have laterally compressed, oval bodies which may be deep, or slender. A few species have a tubular snout. The mouth is very small and is with non protractile jaws which have one row of compressed, closely set, incisor-like teeth in each jaw. The teeth overlap slightly and create a beak like structure. The dorsal fin has 13 robust spines and 10 soft rays and the front spine is short, sharp and points forward, sometimes projecting from its "pocket" but it may be enfolded. The anal fin has 7 robust spines and 9 soft rays. The pelvic fins have 2 spines with 3 soft rays between them; this characteristic is unique to the Siganidae. There is a membrane which extends from the inner pelvic fin spine to the belly with the anus sitting between these membranes. The tiny scales are cycloid and may be absent from the head region. If present on the head they are restricted to a small area of the cheek under the eye. The fin spines are equipped with well-developed venom glands. The sting is very painful, but it is generally not considered medically significant in healthy adults. They range in maximum total lengths of 20 cm (7.9 in) in the case of the blotched foxface (S. unimaculatus) to 53 cm (21 in) in the streaked spinefoot (S. javus).




Distribution and habitat


Rabbitfishes are found in the Indo-Pacific from the Red Sea and the coast of eastern Africa through the Pacific Ocean as far as Pitcairn Island. Two Red Sea species S. rivulatus and S. luridus have invaded the Mediterranean Sea through the Suez Canal, a process known as Lessepsian migration. These fishes are found in inshore tropical and subtropical waters where they occur in reefs, lagoons, mangroves and seagrass beds.




Biology


All rabbitfish are diurnal; some live in schools, while others live more solitary lives among the corals. Rabbitfish sleep in crevices in the reef matrix at night. While sleeping, the rabbitfish Siganus canaliculatus was observed being cleaned by the cleaner shrimp Urocaridella antonbruunii. They are herbivorous, feeding on benthic algae in the wild. However, Siganus rivulatus was recently observed feeding on jellyfish (Scyphozoa) and comb jellies (Ctenophora) in the Red Sea. Also Siganus fuscescens have been observed eating prawns and other baits, suggesting that some species are opportunistic omnivorous feeders. The live passage of benthic organisms in the guts of invasive rabbitfish (ichthyochory) was shown to play a major role in the long distance dispersal and bioinvasion of foraminifera. Rabbitfish lay adhesive eggs and some species live as monogamous pairs.




Venom


Rabbitfish have venomous spines in the dorsal and pelvic fins. In at least one species the venom has been found to be similar to that found in stonefish.




Utilization


Rabbitfish can be important species for commercial fisheries, particularly the schooling species. The catch is largely sold fresh but juveniles may be dried or processed to make fish paste. Some species are used in aquaculture and some of the more colorful species are found in the aquarium trade.
Some species have been reported to be hallucinogenic.




References

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