Comephorus
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''Comephorus'', known as the golomyankas or Baikal oilfish, are a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
comprising two
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of peculiar,
sculpin A sculpin is a type of fish that belongs to the superfamily Cottoidea in the order Perciformes.Kane, E. A. and T. E. Higham. (2012)Life in the flow lane: differences in pectoral fin morphology suggest transitions in station-holding demand acros ...
fishes
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
to
Lake Baikal Lake Baikal is a rift lake and the deepest lake in the world. It is situated in southern Siberia, Russia between the Federal subjects of Russia, federal subjects of Irkutsk Oblast, Irkutsk Oblasts of Russia, Oblast to the northwest and the Repu ...
in Russia. ''Comephorus'' is the only genus in the
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
Comephorinae. Golomyankas are
pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...
fishes and the main food source for the
Baikal seal The Baikal seal (''Pusa sibirica''), also known as Lake Baikal seal or Baikal nerpa (), is a species of earless seal endemic to Lake Baikal in Siberia, Russia. The Baikal seal is one of the smallest earless/true seals, and the only exclusively ...
.


Taxonomy

''Comephorus'' was first proposed as a
monospecific genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
in 1800 by the French
naturalist Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is cal ...
and politician
Bernard Germain de Lacépède Bernard-Germain-Étienne de La Ville-sur-Illon, comte de Lacépède or La Cépède (; 26 December 17566 October 1825) was a French natural history, naturalist and an active freemason. He is known for his contribution to the Comte de Buffon's g ...
with ''Callionymus baikalensis'' as its only species. The 5th edition of ''
Fishes of the World ''Fishes of the World'' is a standard reference for the systematics of fishes. It was first written in 1976 by the American ichthyologist Joseph S. Nelson (1937–2011). Now in its fifth edition (2016), the work is a comprehensive overview of t ...
'' places this genus in the
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
subfamily Comephorinae within the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Cottidae The Cottidae are a family of fish in the superfamily Cottoidea, the sculpins. It is the largest sculpin family, with about 275 species in 70 genera.Kane, E. A. and T. E. Higham. (2012)Life in the flow lane: differences in pectoral fin morphology ...
, the typical sculpins. Other authorities have used
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
studies which have found that Baikal sculpins that were classified in the subfamilies Comephorinae and
Abyssocottinae The Abyssocottinae are a subfamily of ray-finned fishes in the family Cottidae, the sculpins. They are known commonly as the deep-water sculpins.Froese, R. and D. Pauly. (Eds.Abyssocottidae.FishBase. 2011. The entire subfamily is endemic to Lake ...
by ''Fishes of the World'' radiated from an ancestor which was likely to be within the genus '' Cottus'' and that the classification of the Baikal sculpins in a different taxon from ''Cottus'' was
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
.


Description

''Comephorus'' have translucent bodies with no scales,Animals and plants of Lake Baikal
from Irkutsk State University, accessed May 5, 2006
but appear dull when dead. The big Baikal oilfish (''C. baikalensis'') can reach up to in length and the little Baikal oilfish (''C. dybowskii'') up to . Males are smaller than females, only reaching about the length. They have long
pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...
s, and although pelvic bones are present, they lack
pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...
s. They have a strong
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 epithelia ...
. The lateral line system on the head consists of large cavities linked by narrow, bony bridges with small external pores. High
lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...
content and porous bones result in an almost
neutral buoyancy Neutral buoyancy occurs when an object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink (if the body's de ...
Sideleva, V.G. (1996). Comparative character of the deep-water and inshore cottoid fishes endemic to Lake Baikal. Journal of Fish Biology 49(sA): 192–206. and lack of
swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ (anatomy), organ in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift ...
allows the fish to tolerate varying pressure extremes as they move through the
water column The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...
. Over a third of the body weight (38.9%) of ''C. baikalensis'' is oil, but ''C. dybowskii'' contains far less (4.7%). It has been said that they
decompose Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is essen ...
in sunlight, leaving behind only fatty oil and bones, although the accuracy of this claim has been questioned. Unusually, their eyes only contain
rod cell Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in ...
s (not
cone cell Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most v ...
s), indicating a high sensitivity to light. Some of the adaptions in golomyankas resemble those seen in
deep sea fish Deep-sea fish are fish that live in the darkness below the sunlit surface waters, that is below the epipelagic or photic zone of the sea. The lanternfish is, by far, the most common deep-sea fish. Other deep-sea fishes include the flashlight f ...
.


Species

There are currently two recognized species in this genus: * '' Comephorus baikalensis'' (
Pallas Pallas may refer to: Astronomy * 2 Pallas asteroid ** Pallas family, a group of asteroids that includes 2 Pallas * Pallas (crater), a crater on Earth's moon Mythology * Pallas (Giant), a son of Uranus and Gaia, killed and flayed by Athena * Pa ...
, 1776)
(Big Baikal oilfish) * '' Comephorus dybowskii'' Korotneff, 1904 (Little Baikal oilfish)


Biology and ecology

The common name ''golomyanka'' originates from the old-Russian ''golomen'', meaning "far from the shore" in the local dialect and referring to their
pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...
behavior. They are the principal ecological competitor to the
omul The omul, ''Coregonus migratorius'', also known as Baikal omul (), is a whitefish species of the salmon family endemic to Lake Baikal in Siberia, Russia. It is considered a delicacy and is the object of one of the largest commercial fisheries ...
, which also eat small golomyankas, and represent a primary food source for the
Baikal seal The Baikal seal (''Pusa sibirica''), also known as Lake Baikal seal or Baikal nerpa (), is a species of earless seal endemic to Lake Baikal in Siberia, Russia. The Baikal seal is one of the smallest earless/true seals, and the only exclusively ...
, at more than 90% of its diet. They are easily identifiable, and are large enough to be easily seen. Golomyankas are unusual for occurring pelagically throughout the entire water column of Lake Baikal, ranging from depths of around to near the surface, but they primarily occur deeper than . During the night they move up the water column to feed, often occurring as shallow as , and in the winter they can occasionally be seen swimming just below the ice-covered surface. They are considered the world's most abyssal freshwater fish, together with certain Lake Baikal deep-water sculpins (Abyssocottidae).Hunt, D. M., et al. (1997). Molecular evolution of the cottoid fish endemic to Lake Baikal deduced from nuclear DNA evidence. ''Molecular Phylogenetics and Evolution'' 8(3), 415–22. They move without much regard for changes in pressure, although they can exist only in cold temperatures, preferring water that is no more than and dying at .Ichthyofauna of Lake Baikal
from Baikal Web World, accessed May 5, 2006 (with a photo of the golomyanka).
The
biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...
of the golomyanka population is estimated at about 150 thousand tons, making it the most populous fish in Lake Baikal. It is estimated that about 70% of the fish in the lake are golomyankas. Their juveniles are also the most abundant pelagic
fish larvae Ichthyoplankton (from Greek: wikt:ἰχθύς, ἰχθύς, , "fish"; and πλαγκτός, , "drifter") are the Fish eggs, eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which ...
in the lake. Large
shoals In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or ...
are not known for this species, although groups of up to about 20 individuals have been recorded near the lake bottom. Females are more common than males, which only make up about 32% of the population in the little Baikal oilfish and 17% in the big Baikal oilfish. The females do not lay eggs; rather, they are
viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...
, giving birth to a swarm of 2000–3000 larvae. Females containing developing embryos can be seen year-round, but there does appear to be a level of seasonality in the birth, with the largest number of larvae occurring from August to April (some differences in the peak timing between the two species). Most females die after giving birth. It has been claimed that their bellies burst open to release the young, killing the female in the process, but this is a myth. Golomyanka can reach an age of up to 6–8 years. They are sluggish fish, and have relatively large mouths with several rows of somewhat brush-like teeth, allowing them to sift out fine organisms from the water. They primarily feed on the planktonic copepod '' Epischura baikalensis'', the
amphipod 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 10,700 amphipod species cur ...
crustacean '' Macrohectopus branickii'' and larvae of
sculpin A sculpin is a type of fish that belongs to the superfamily Cottoidea in the order Perciformes.Kane, E. A. and T. E. Higham. (2012)Life in the flow lane: differences in pectoral fin morphology suggest transitions in station-holding demand acros ...
s,Miyasaka, Dzyuba, Genkai-Kato and Wada (2006). Feeding ecology of two planktonic sculpins, Comephorus baicalensis and Comephorus dybowskii (Comephoridae), in Lake Baikal. Ichthyological Research 53(4): 419–422. including those of their own species.


Relationship to humans

Despite being numerous in the lake, golomyankas are difficult to catch in large quantities as they do not gather in large schools. Golomyankas are not harvested commercially, although their fats and oils were used in lamps and as
traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) refers to the knowledge, skills, and practices rooted in the cultural beliefs of various societies, especially Indigenous groups, used for maintaining health and treatin ...
by native Siberians when storms tossed the fish up on shore. They are of no value as a food source for humans, dogs or cats, but are the primary food source for the Baikal seal, and also eaten by other fish in the lake. They are so numerous and spawn so rapidly that they represent the largest concentration of fish biomass within the entire lake, and would seriously unbalance the ecosystem of Lake Baikal if not constantly preyed upon by
predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
s.


See also

*
List of fish families This is a list of fish families sorted alphabetically by scientific name. There are 525 families in the list. __NOTOC__ A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - R - S - T - U - V - W - X - Y - Z - ...


References


Lake Baikal FAQ
Irkutsk State University Lake Baikal FAQ, accessed May 5, 2006 {{Taxonbar, from=Q803775 Cottoidei Scorpaeniformes genera Viviparous fish Taxa named by Bernard Germain de Lacépède Endemic fauna of Russia Fish of Lake Baikal