The thickback sole (''Microchirus variegatus''), also known as the bastard sole and lucky sole, is a species of

flatfish A flatfish is a member of the Ray-finned fish, ray-finned demersal fish order (biology), order Pleuronectiformes, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the ...

from the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of true soles, the

Soleidae The true soles are a family, Soleidae, of flatfishes. It includes saltwater and brackish water species in the East Atlantic, Indian Ocean, and West and Central Pacific Ocean. Freshwater species are found in Africa, southern Asia, New Guinea, an ...

. It is found in the eastern Atlantic Ocean and 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 ...

, it is a quarry for fisheries in the Mediterranean.

Description

The thickback sole has the typical slender, elongated, oval body shape of soles but which is thick from side to side. It has a smoothly rounded snout. small head with a strongly curved mouth on its underside. They have large eyes which have a diameter which is greater than the length of the snout. The

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 ...

has its origin near the front of its upper eye and has a smooth profile with 63-80 fin rays, 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 ...

is shorter with 47-64 fin rays. The caudal fin is separate from last rays of the dorsal and anal fins. The

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 ...

has 65-98 pored scales. It has small

pectoral 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 ...

s with the one on the blind side being minute. The eyed side is brown in colour with five transverse black bands which reach to the dorsal and anal fins creating dark patches on these fins. The largest fish recorded had a

standard length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish m ...

of 35 cm, they are more normally recorded with a total length of 14 cm.

Distribution

The thickback sole occurs in the northeast Atlantic, from Great Britain and Ireland south to the Baie du Lévrier in Senegal, they are also found around

Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...

. In the Mediterranean Sea, this species can be found throughout the basin except for the coasts of the

Levantine Sea The Levantine Sea (Arabic: بحر الشام, tr, Levanten Denizi, el, Θάλασσα του Λεβάντε) is the easternmost part of the Mediterranean Sea. Geography The Levantine Sea is bordered by Turkey in the north and north-east co ...

Habitat and biology

This species is

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

on sea beds consisting of sand and mud, preferring coarse sand. on the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

and

slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

, at depths between 80–400 m. It feeds on a wide range of small benthic organisms, largely crustaceans such as amphipods and

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

, also polychaetes and

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

. The spawning season runs from early March to early summer in the

English Channel The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais) or ( Jèrriais), (Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kana ...

but from late winter and spring to early autumn off Ireland. They can live for up to 14 year. The young thickback sole develop in open-sea nurseriesand settle into a benthic mode at a relatively young age compared to

common sole The common sole, Dover sole, or black sole (''Solea solea'') is a species of flatfish in the family Soleidae. It is one of the largest fish in the ''Solea'' genus. It lives on the sandy or muddy seabed of the northern Atlantic and the Mediterra ...

and this may be why they are rarely recorded in coastal waters.

Fisheries

The thickback sole is not utilized in fisheries in the central eastern Atlantic but in the Mediterranean it is a commercially exploited species and is regularly observed in markets in Morocco, the

Tyrrhenian Sea The Tyrrhenian Sea (; it, Mar Tirreno , french: Mer Tyrrhénienne , sc, Mare Tirrenu, co, Mari Tirrenu, scn, Mari Tirrenu, nap, Mare Tirreno) is part of the Mediterranean Sea off the western coast of Italy. It is named for the Tyrrhenian pe ...

and the

Adriatic Sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to t ...

. Elsewhere it is not common in markets. The flesh is highly esteemed and is marketed both fresh and frozen. The average depth of commercial trawls in the Atlantic is between 35m and 200m and this could mean that thickback soles are caught in a significant amount as bycatch and that most are discarded, the effects of this bycatch on the population is not known. The commercial fisheries for thickback sole in the Mediterranean uses trawls, gill and trammel nets.

References

{{Taxonbar, from=Q2352439 Soleidae Fish described in 1808