Classification of Chimaera (Rat Fish)

• Phylum :- Chordata (Dorsal tubular nerve cord, notochord and gill-slits present.)
• Group :- Craniata (Cranium with brain present.)
• Sub phylum :- Vertebrata (Vertebral column present.)
• Division :- Gnathostomata (Jaws and paired appendages present.)
• Super Class :- Pisces (Paired fins, gills and skin with scales.)
• Class :- Chondrichthyes (=Elasmobranchii) (Endoskeleton cartilaginous. Scales usually placoid. Notochord rudimentary, Spiral valve in intestine, opercula absent)
• Sub-Class :- Bradyodonti (Dentition of crushing type.)
• Order :- Holocephali (Spiracle absent. Operculum present. Skull autostylic with two dorsal fms and an anal fin.)
• Family :- Chimaeridae (Body elongated and shark-like.)
• Genus :- Chimaera (Rat Fish)

Geographical distribution

They inhabits the European coasts from Norway to Portugal, Japan and North America. Upper Devonian to Recent.

Habit and habitat

It is found at the depth of 350 to 2200 metres and eats fish, invertebrates and seaweeds.

General Characteristics of Chimaera (Rat Fish)

• Commonly known as ‘Rat Fish’ or ‘King of Herrings’. Body divisible into head, trunk and tail.
• Body is shark-like with compressed head and blunt snout. Mouth is bounded by lip-like folds.
• Mouth and nostril ventral in position.
• Gill-slits communicate with the exterior by a single branchial opening below the operculum which is not bony and covers the gills.
• Spiracles absent.
• There are two large dorsal fins and a small ventral fin.
• First dorsal fin bears an immensely bony anterior erectile dermal spine while the second dorsal fin is non-erectile.
• The paired pectoral and pelvic fins are enlarged. Ventral fin small.
• Caudal fin is like a folded tail, is produced into whip-like filament and is of diphyceral type.
• Sexes are separate.
• Male Chimaera contains five claspers, a frontal or cephalic clasper on the head, a pair of anterior claspers in front of pelvic fins and a pair of ordinary claspers near pelvic fins.
• Lateral line consists of open groove and body surface is smooth and scaleless.
• Male fish contains claspers. Jaw suspension autostylic.
• Eggs are surrounded by egg shell. Placoid scales are found in young rat fish.

Economic importance

The Ratfish, also known as ghost sharks, belong to the subclass Holocephali and are known for their unique appearance and ecological role in marine environments. They hold economic importance in several areas, as described below:

1. Fisheries and Trade

• Meat Consumption: In some regions, chimaera meat is consumed locally, though it is not as widely traded as other fish species. It is often marketed as a low-cost protein source.
• Liver Oil: The liver of chimaera fish is rich in oil, which is used in pharmaceuticals, cosmetics, and industrial applications. This oil is particularly valued for its squalene content, which has moisturizing and antioxidant properties.
• Bycatch Utilization: Although often caught as bycatch in deep-sea fisheries, efforts to process and utilize these fish have increased their economic relevance in some regions.

2. Scientific Research

• Evolutionary Studies: As one of the oldest surviving groups of jawed vertebrates, chimaera ratfish are of significant interest to evolutionary biologists. Their unique characteristics provide insights into the evolution of cartilaginous fish and vertebrate anatomy.
• Biomimicry and Robotics: The hydrodynamic body structure and swimming mechanics of chimaeras inspire innovations in underwater robotics and biomimetic designs.
• Medical Research: The cartilage of chimaeras is studied for potential applications in medical treatments, including joint health and regenerative medicine.

3. Industrial Uses

• Cartilage Extraction: Cartilage is sometimes processed into products for dietary supplements, believed to support joint and bone health.
• Skins and Byproducts: Their skin, while less commonly utilized, can be processed into materials for niche industrial applications.

4. Ecotourism and Educational Value

• Exhibits and Awareness: Chimaeras are often displayed in aquariums and marine exhibits, where they attract visitors due to their unusual appearance and rarity. These exhibits generate revenue and raise awareness about deep-sea biodiversity.
• Conservation Tourism: Deep-sea diving expeditions in regions where chimaeras are found contribute indirectly to local economies through ecotourism.

Challenges and Sustainability

Chimaeras are particularly vulnerable to overfishing and habitat degradation due to their deep-sea habitats and slow reproduction rates. These factors make sustainable management critical for preserving their populations.

Sustainability Measures:

1. Fishing Regulations: Monitoring and regulating deep-sea trawling to reduce bycatch and overexploitation of chimaeras.
2. Protected Areas: Establishing marine protected zones to safeguard their habitats from industrial activities.
3. Research Funding: Supporting studies to better understand their ecological roles and population dynamics.
4. Public Awareness: Educating the public on the ecological importance of chimaeras and promoting sustainable use of their resources.

By balancing their economic value with conservation efforts, chimaera ratfish can continue to provide benefits to humans while maintaining their essential role in marine ecosystems.

Special features

• Chimaera is important because it shows selachian and certain specialized characters. Selachian features comprise of cartilaginous endoskeleton, selachian limb girdles, dermal denticles, absence of air bladder, presence of spiral valve in the intestine, conus arteriosus and claspers in male.
• The specialized characters include autostylic skull, firmly fused palato-quadrate with the base of cranium, teeth in the form of crushing dental plates and five claspers in male. The fish also reveals tendencies towards the bony fishes in having crowded gill-slits beneath the head covered by operculum, suppressed spiracles and absence of cloaca. Chimaera is an interesting fish, intermediate between sharks and bony fishes. Like sharks they have a skeleton of cartilage but unlike them Chimaera has small fleshy lipped mouth with tooth plates attached to jaw. Spiracles absent. Chimaera further resembles the bony fishes in lacking cloaca and in having urinogenital aperture behind anus.

Identification

Since this fish has blunt snout, additional claspers and above features, hence it is Chimaera.