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), suborder Pleuronectoidei, also called the Heterosomata. In many species, both eyes lie on one side of the head, one or the other migrating through or around ...

from 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 ...

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, West and Central Pacific Ocean, and the mediterranean sea. Freshwater species are found in Africa, souther ...

. 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 east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

, 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 on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

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 moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

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 epithelia ...

has 65-98 pored scales. It has small

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 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 fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...

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 Madeira ( ; ), officially the Autonomous Region of Madeira (), is an autonomous Regions of Portugal, autonomous region of Portugal. It is an archipelago situated in the North Atlantic Ocean, in the region of Macaronesia, just under north of ...

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

Levantine Sea The Levantine Sea () is the easternmost part of the Mediterranean Sea. Geography The Levantine Sea is bordered by Turkey in the north and north-east corner, Syria, Lebanon, Israel, and Palestine in the east, Egypt in the south, and the Aegean ...

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 the Ancient Greek word (), meaning "the depths". ...

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 islan ...

and

slope In mathematics, the slope or gradient of a Line (mathematics), line is a number that describes the direction (geometry), direction of the line on a plane (geometry), plane. Often denoted by the letter ''m'', slope is calculated as the ratio of t ...

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

amphipods Amphipoda () is an order (biology), 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 amphip ...

and

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

, also

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

s and

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

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

English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...

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 Mediter ...

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 (, ; or ) , , , , is part of the Mediterranean Sea off the western coast of Italy. It is named for the Tyrrhenians, Tyrrhenian people identified with the Etruscans of Italy. Geography The sea is bounded by the islands of C ...

and the

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

. 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