Grooved carpet shell
Encyclopedia
The grooved carpet shell, Ruditapes decussatus, is a clam
or bivalve mollusc in the family
Veneridae
. It is distributed worldwide and due to its ecological and economic interest has been proposed as a bioindicator
.
This species is one of the most popular and profitable mollusc of lagoonal and coastal sites in the Mediterranean, where it was collected for a long time as food. It is consumed fresh and canned.
is broadly oval to quadrate with the umbones distinctly anterior. The posterior hinge line is straight, the posterior margin truncate, and the anterior hinge line grades into the down-sloping anterior margin. It is prominent posteriorly, where the shell is conspicuously decussate. The surface has a sculpture
of fine concentric striae and bolder radiating lines. Growth stages are clear. The lunule and escutcheon are poorly defined. Each valve has three cardinal teeth: the centre one in the left valve, and centre and posterior in right are bifid. The pallial line and adductor scars are distinct. The pallial sinus is U-shaped, not extending beyond the midline of the shell, but reaching a point below the posterior part of the ligament. The lower limb of the sinus is distinct from the pallial line for the whole of its length. The inner surfaces of the shell are glossy white, often with yellow or orange tints, and with a bluish tinge along the dorsal edge. The overall color is cream, yellowish, or light brown, often with darker markings.
that filters water
through its two siphons (one in and the other out) catching organic matter (detritus) and phytoplankton
as food. The gills are two pairs of plates composed of filaments. Clams live on the sandy beaches of the Rias (flooded river valleys). Ruditapes decussatus is buried 15–20 cm deep in the sand from the middle of the intertidal zone
to a depth of a few metres. Its sexes are separate, although hermaphrodite
s can be found infrequently. Reproduction is external and takes place mainly during summer in the wild, and/or in hatcheries. In spring, clams can be artificially conditioned for hatching with higher temperature water and abundant food. The larva
e swim freely for 10–15 days before settling as spat of about 0.5 mm on a sand and silty mud substrate.
, Spain
and France
. In Spain, early records of mollusc fishing and consumption from the 16th century are mainly about the flat oyster, and only rarely about clams
, but they do mention the marketing of clams in Portugal and other places. Intensive fishing for clams began in 1926 and 1927. Digging was indiscriminate, as fishermen used prohibited tools and took clams of all sizes. In Spain, near San Simon, in the Ria de Vigo
, fishermen found one natural clam population and depleted it in a short time. The fishermen sold cases of clams weighing 54 kg for only 5 pesetas (€ 0.03). Later, when competition increased, the price became 30 pesetas (€ 5.55). In 1935, clam fishing was regulated and the quantity of clams each fisherman was allowed to take during each low tide was 14 kg, and the season was closed from May to October. At that time, there were 6,130 walking harvesters and 1,480 others using boats near San Simon.
Despite the large clam harvests, their repopulation is rapid. In 1948 it was estimated that populations of Ruditapes decussatus and Venerupis pullastra in the Ria del Burgo (Spain) recovered in less than a year from a density of 1–5 to 30–50 clams/m2. Production of clams from 1927 to 1953 in the Ria de Vigo ranged from 28,719 to 652,890 kg. Around 1956, clam production in the Galician region was about 60 percent of national production. The season was from October to March, while in areas nearest to the mouth of the Ria about 60 boats worked and obtained 3,000 kg per day. These differences were associated with the great mortality that occurred in the inner part of the Ria de Vigo, due to heavy rains that produced a rapid drop in salinity. In the ensuing years, clam production has been variable, and statistical data on total production is sparse.
The history of shell fisheries in the Galician region (Spain) shows that molluscs were managed improperly, and various species were impacted. The first to be depleted was the flat oyster, Ostrea edulis; after that, the digging of cockles
and clams began, and as Ruditapes decussatus became scarcer, the digging of Venerupis pullastra and Venerupis rhomboideus began. Currently, the populations of the other commercial bivalves are declining. Besides heavy fishing, clams declined because pollution increased and the seaports and urban areas grew, degrading their habitat. However, some regions in the Atlantic coast of the Iberian Peninsula
, and of the Mediterranean basin
, as well as Ireland
, currently have solid populations of Ruditapes decussatus.
This species is one of the most popular and profitable mollusc of lagoonal and coastal sites in the Mediterranean, where it was collected for a long time as food. But this kind of harvesting did not satisfy the market, and the culture of this species was started in some lagoon areas, mainly in Italy. However, as its farming was not completely successful, it was replaced in the early 1980s by a related Pacific species, T. philippinarum. Food and Agriculture Organization
's (FAO) Yearbook of Fishery Statistics reports a range of yearly production from around 2,019 mt in 1995 to 1,823 mt in 1999 (France, Ireland, Portugal, Spain, Tunisia). FAO's Yearbook of Fishery Statistics reports a range of yearly aquaculture production from around 7,233 mt in 1995 to 4,422 mt in 1999 (France, Portugal, Spain).
, Spain
, Portugal
and in the Mediterranean basin
. It is often grown with other bivalves (Venerupis pullastra, Venerupis rhomboideus, Venerupis aurea, Dosinia exoleta and Tellina incarnate). Their main predators are shore crabs (Carcinus maenas
); starfish (Asterias rubens
and Marthasterias glaciais); gastropods (Natica sp.); and birds (Larus sp). An individual Carcinus maenas (6.5 cm width) can consume 5 or 6 clams per day. Marine aquaculture production of grooved carpet shell in 2003 was 3,007 t in Portugal, which excludes non-aquaculture harvesting of the species.
Between 1997 and 2001 total aquaculture
production varied between 3,700 and 4,900 tonnes, from five countries. Most was produced by Portugal
but France
and Spain
have also been significant producers; however, the contribution from France is now much lower than before; in 1995 it was by far the leading producer with nearly 5,200 tonnes but in 2004 it produced only 475 tonnes, possibly due to disease problems, notably brown ring disease. Global production seems to be declining; in 2004 it was only 2,700 tonnes but the United Kingdom
had appeared as a minor producer.
The shelf life of the grooved carpet shell is extremely long (several days out of water, depending on environmental conditions), making this species very desirable, and it obtains high prices in the market. These clams are sold in local supermarkets, popular markets, hotels, and restaurants, including those in Madrid
, Lisbon
, Barcelona
, and the Algarve. Prices vary according to their abundance in the market. However, as an approximation, in 1985 the price was about € 0.60/kg. In 2005, the price for live Ruditapes decussatus in Spain was about € 15/kg. It is consumed fresh and canned.
s. Gamete liberation can be induced by raising the temperature from 10 to 26°C, maintaining it at that temperature for 30 minutes and then reducing it to 15°C for several minutes; the cycle of raising temperature to 26°C and lowering it again is then repeated until gametes are liberated. The addition of sperm from a sacrificed animal may also help in liberation. Fertilization occurs in small containers where the animals are isolated from each other. Eggs are filtered through a 40 µm mesh, and transferred to a 10 litre tank, where veliger
larvae appear after 48 hours. Larvae are recollected in a 40 µm mesh and reared at densities of 3,000 larvae/litre. They are fed with unicellular algae every day during the first week and then every second day until metamorphosis.
in areas where mussels are not available. The accumulation of several anthropogenic compounds in their tissues suggests that they possess mechanisms that allow them to cope with the toxic effects of these contaminants. Besides pollutant uptake, the use of biomarkers is pointed out since it is a promising approach to monitor the effect of these contaminants in the marine environment. Biomarkers complement the information of the direct chemical characterization of different types of contaminants. Therefore, the role of several biomarkers: (metallothionein
s (MT), superoxide dismutase
(SOD), catalase
(CAT), glutathione peroxidase
s (GPx) (total and selenium
-dependent), lipid peroxidation
(measured as MDA, one of the final products of lipid peroxidation), glutathione S-transferase
(GST) and acetylcholinesterase
(AChE), were measured in different tissues of the clam Ruditapes decussatus, in laboratory conditions and under various environmental stresses, in two ecosystems (Ria Formosa lagoon, Portugal
; and Bizerta lagoon, Tunisia
) in a perspective of a multibiomarker approach to assess environmental changes. Experiment and field studies were in good agreement since MT levels, especially in the gills, the first target tissue of these contaminants, can be used as biomarker of exposure to Cd. GPx and MDA may also be determined in this respect. AChE activity is inhibited by pesticide
and, to a less extent, by metal exposure in the gills and whole soft body of clams. However, the induction of GST isoforms experimentally demonstrated is not observed in the field because only global GST activity was determined. The whole set of results opened new perspectives for the use of this species to assess the effect of mixtures of pollutants in the aquatic environment.
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...
or bivalve mollusc in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Veneridae
Veneridae
The Veneridae or venerids, also known as the Venus clams, are a very large family of minute to large, saltwater clams, marine bivalve molluscs. There are over 500 living species of venerid bivalves, most of which are edible, and many of which are exploited as a food source.Many of the most...
. It is distributed worldwide and due to its ecological and economic interest has been proposed as a bioindicator
Bioindicator
Biological indicators are species used to monitor the health of an environment or ecosystem. They are any biological species or group of species whose function, population, or status can be used to determine ecosystem or environmental integrity. An example of such a group are the copepods and other...
.
This species is one of the most popular and profitable mollusc of lagoonal and coastal sites in the Mediterranean, where it was collected for a long time as food. It is consumed fresh and canned.
Description
The shellMollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
is broadly oval to quadrate with the umbones distinctly anterior. The posterior hinge line is straight, the posterior margin truncate, and the anterior hinge line grades into the down-sloping anterior margin. It is prominent posteriorly, where the shell is conspicuously decussate. The surface has a sculpture
Sculpture (mollusc)
The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...
of fine concentric striae and bolder radiating lines. Growth stages are clear. The lunule and escutcheon are poorly defined. Each valve has three cardinal teeth: the centre one in the left valve, and centre and posterior in right are bifid. The pallial line and adductor scars are distinct. The pallial sinus is U-shaped, not extending beyond the midline of the shell, but reaching a point below the posterior part of the ligament. The lower limb of the sinus is distinct from the pallial line for the whole of its length. The inner surfaces of the shell are glossy white, often with yellow or orange tints, and with a bluish tinge along the dorsal edge. The overall color is cream, yellowish, or light brown, often with darker markings.
Biology and habitat
The grooved carpet shell lives burrowed in sand and silty mud. It is a lamellibranch bivalve molluscBivalvia
Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...
that filters water
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
through its two siphons (one in and the other out) catching organic matter (detritus) and phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
as food. The gills are two pairs of plates composed of filaments. Clams live on the sandy beaches of the Rias (flooded river valleys). Ruditapes decussatus is buried 15–20 cm deep in the sand from the middle of the intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
to a depth of a few metres. Its sexes are separate, although hermaphrodite
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
s can be found infrequently. Reproduction is external and takes place mainly during summer in the wild, and/or in hatcheries. In spring, clams can be artificially conditioned for hatching with higher temperature water and abundant food. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e swim freely for 10–15 days before settling as spat of about 0.5 mm on a sand and silty mud substrate.
Historical background
The harvesting of Ruditapes decussatus mainly occurs in PortugalPortugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
and France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. In Spain, early records of mollusc fishing and consumption from the 16th century are mainly about the flat oyster, and only rarely about clams
CLaMS
CLaMS is a modular chemistry transport model system developed at Forschungszentrum Jülich, Germany. CLaMS was first described by McKenna et al. and was expanded into three dimensions by Konopka et al....
, but they do mention the marketing of clams in Portugal and other places. Intensive fishing for clams began in 1926 and 1927. Digging was indiscriminate, as fishermen used prohibited tools and took clams of all sizes. In Spain, near San Simon, in the Ria de Vigo
Ria de Vigo
Vigo Ria is a ria in Galicia, Spain. It is the southern most ria of the Rias Baixas.The following German U-Boats are reported to have been sunk somewhere in the ria: the U-523, sunk August 25, 1943 , and the U-506, sunk at 15:50 hrs on July 12, 1943 .-External links:*...
, fishermen found one natural clam population and depleted it in a short time. The fishermen sold cases of clams weighing 54 kg for only 5 pesetas (€ 0.03). Later, when competition increased, the price became 30 pesetas (€ 5.55). In 1935, clam fishing was regulated and the quantity of clams each fisherman was allowed to take during each low tide was 14 kg, and the season was closed from May to October. At that time, there were 6,130 walking harvesters and 1,480 others using boats near San Simon.
Despite the large clam harvests, their repopulation is rapid. In 1948 it was estimated that populations of Ruditapes decussatus and Venerupis pullastra in the Ria del Burgo (Spain) recovered in less than a year from a density of 1–5 to 30–50 clams/m2. Production of clams from 1927 to 1953 in the Ria de Vigo ranged from 28,719 to 652,890 kg. Around 1956, clam production in the Galician region was about 60 percent of national production. The season was from October to March, while in areas nearest to the mouth of the Ria about 60 boats worked and obtained 3,000 kg per day. These differences were associated with the great mortality that occurred in the inner part of the Ria de Vigo, due to heavy rains that produced a rapid drop in salinity. In the ensuing years, clam production has been variable, and statistical data on total production is sparse.
The history of shell fisheries in the Galician region (Spain) shows that molluscs were managed improperly, and various species were impacted. The first to be depleted was the flat oyster, Ostrea edulis; after that, the digging of cockles
Cockle (bivalve)
Cockle is the common name for a group of small, edible, saltwater clams, marine bivalve molluscs in the family Cardiidae.Various species of cockles live in sandy sheltered beaches throughout the world....
and clams began, and as Ruditapes decussatus became scarcer, the digging of Venerupis pullastra and Venerupis rhomboideus began. Currently, the populations of the other commercial bivalves are declining. Besides heavy fishing, clams declined because pollution increased and the seaports and urban areas grew, degrading their habitat. However, some regions in the Atlantic coast of the Iberian Peninsula
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
, and of the Mediterranean basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...
, as well as Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
, currently have solid populations of Ruditapes decussatus.
This species is one of the most popular and profitable mollusc of lagoonal and coastal sites in the Mediterranean, where it was collected for a long time as food. But this kind of harvesting did not satisfy the market, and the culture of this species was started in some lagoon areas, mainly in Italy. However, as its farming was not completely successful, it was replaced in the early 1980s by a related Pacific species, T. philippinarum. Food and Agriculture Organization
Food and Agriculture Organization
The Food and Agriculture Organization of the United Nations is a specialised agency of the United Nations that leads international efforts to defeat hunger. Serving both developed and developing countries, FAO acts as a neutral forum where all nations meet as equals to negotiate agreements and...
's (FAO) Yearbook of Fishery Statistics reports a range of yearly production from around 2,019 mt in 1995 to 1,823 mt in 1999 (France, Ireland, Portugal, Spain, Tunisia). FAO's Yearbook of Fishery Statistics reports a range of yearly aquaculture production from around 7,233 mt in 1995 to 4,422 mt in 1999 (France, Portugal, Spain).
Production and harvesting
Ruditapes decussatus is cultured from the Atlantic coast of FranceFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
and in the Mediterranean basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...
. It is often grown with other bivalves (Venerupis pullastra, Venerupis rhomboideus, Venerupis aurea, Dosinia exoleta and Tellina incarnate). Their main predators are shore crabs (Carcinus maenas
Carcinus maenas
Carcinus maenas is a common littoral crab, and an important invasive species, listed among the 100 "world's worst alien invasive species". It is native to the north-east Atlantic Ocean and Baltic Sea, but has colonised similar habitats in Australia, South Africa, South America and both Atlantic and...
); starfish (Asterias rubens
Common starfish
The Common Starfish or Common Sea Star is the most common and familiar starfish in the north-east Atlantic. It has five arms and usually grows to between 10–30 cm across, although larger specimens are known. The Common Starfish is usually orange or brown, and sometimes violet;...
and Marthasterias glaciais); gastropods (Natica sp.); and birds (Larus sp). An individual Carcinus maenas (6.5 cm width) can consume 5 or 6 clams per day. Marine aquaculture production of grooved carpet shell in 2003 was 3,007 t in Portugal, which excludes non-aquaculture harvesting of the species.
Between 1997 and 2001 total aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
production varied between 3,700 and 4,900 tonnes, from five countries. Most was produced by Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
but France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
and Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
have also been significant producers; however, the contribution from France is now much lower than before; in 1995 it was by far the leading producer with nearly 5,200 tonnes but in 2004 it produced only 475 tonnes, possibly due to disease problems, notably brown ring disease. Global production seems to be declining; in 2004 it was only 2,700 tonnes but the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
had appeared as a minor producer.
The shelf life of the grooved carpet shell is extremely long (several days out of water, depending on environmental conditions), making this species very desirable, and it obtains high prices in the market. These clams are sold in local supermarkets, popular markets, hotels, and restaurants, including those in Madrid
Madrid
Madrid is the capital and largest city of Spain. The population of the city is roughly 3.3 million and the entire population of the Madrid metropolitan area is calculated to be 6.271 million. It is the third largest city in the European Union, after London and Berlin, and its metropolitan...
, Lisbon
Lisbon
Lisbon is the capital city and largest city of Portugal with a population of 545,245 within its administrative limits on a land area of . The urban area of Lisbon extends beyond the administrative city limits with a population of 3 million on an area of , making it the 9th most populous urban...
, Barcelona
Barcelona
Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...
, and the Algarve. Prices vary according to their abundance in the market. However, as an approximation, in 1985 the price was about € 0.60/kg. In 2005, the price for live Ruditapes decussatus in Spain was about € 15/kg. It is consumed fresh and canned.
Seed supply
Farmers obtain seed from their own parks (protected bottoms) or from the natural clam populations in the spring. They dig the clam seed with sand using a small shovel, pass it through a sieve to retain the seed, take it to their ongrowing parks, and spread it in densities of about 800 clams/m2. They may also dig adult clams from seaport areas and spread them in their parks. Periodically, they have to clean their parks of predators and mud.Hatchery production
Seed can also be obtained from hatcheries, where breeders, not exceeding 40 mm are maintained for 30–40 days at 20°C. Breeders are fed with unicellular algae until the induction of the liberation of gameteGamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s. Gamete liberation can be induced by raising the temperature from 10 to 26°C, maintaining it at that temperature for 30 minutes and then reducing it to 15°C for several minutes; the cycle of raising temperature to 26°C and lowering it again is then repeated until gametes are liberated. The addition of sperm from a sacrificed animal may also help in liberation. Fertilization occurs in small containers where the animals are isolated from each other. Eggs are filtered through a 40 µm mesh, and transferred to a 10 litre tank, where veliger
Veliger
A veliger is the planktonic larva of many kinds of marine and freshwater gastropod molluscs, as well as most bivalve mollusks.- Description :...
larvae appear after 48 hours. Larvae are recollected in a 40 µm mesh and reared at densities of 3,000 larvae/litre. They are fed with unicellular algae every day during the first week and then every second day until metamorphosis.
Nursery
Clams can be reared in nurseries within greenhouses, with controlled feeding by using unicellular algae or reared in meshed containers over culture tables. An alternative is to pump environmentally controlled water to inland tanks where clams are placed in cylinders of about 50 cm diameter and 20 cm long, with a bottom made of a rigid mesh.Ongrowing techniques
Culture techniques are simple, consisting of regular maintenance of the substrate, avoiding algae, starfish and other predators; oxygenating the substrate; and maintaining an appropriate clam density and seeding juvenile clams.Harvesting techniques
In the Galician region, fishermen harvest clams by walking the intertidal areas and using special hand shovels, or sometimes by using the rakes that are normally used for keeping the culture beds clear of seaweed. Clams may also be harvested from boats, which may vary in size between less than 1 tonne and up to 12 tonnes. Some are propelled with oars, others with outboard engines. Various collection tools are used, including the 'rastro' and the 'raño' (rake), which are operated from the boats with the help of a long handle. The closed season is from March to October, and the minimum size allowed for Ruditapes decussatus is 30 mm. Some Galician areas have protected bottoms called 'parks' for the extensive culture of clams. In hand (walking) harvesting clams are harvested with the help of different types of small shovels; sometimes the rakes that are usually more employed for cleaning the parks of seaweeds are employed.Handling and processing
Fishermen bring their clams to depuration stations where they are held in tanks for at least 42 hours. The clams are then packed in net bags of 0.5, 1, and 2 kg, and are destined to be canned or eaten fresh. They are transported by refrigerated trucks which maintain their temperature at 3 – 10°C; the clams have a shelf life of 5 days. Canned clams are prepared with vinegar and various sauces. In the Galician region, the most popular meal with clams is 'ameixas a marineira' (mariner clams). The clams are opened in salted water and cooked with a special sauce (onions, garlic, parsley, bread grind and white wine).Production costs
Production costs are greatly influenced by the socio-economic environment and the size of seed supplied. If nursery time starts in spring, harvesting occurs in the late fall or early winter of the following year. Important factors in total costs are seabed leases or exploitation charges hatchery and nursery facility costs, management and harvesting tools and labour.Bioindicator
The clam Ruditapes decussatus is distributed worldwide and due to its ecological and economical interest has been proposed as a bioindicatorBioindicator
Biological indicators are species used to monitor the health of an environment or ecosystem. They are any biological species or group of species whose function, population, or status can be used to determine ecosystem or environmental integrity. An example of such a group are the copepods and other...
in areas where mussels are not available. The accumulation of several anthropogenic compounds in their tissues suggests that they possess mechanisms that allow them to cope with the toxic effects of these contaminants. Besides pollutant uptake, the use of biomarkers is pointed out since it is a promising approach to monitor the effect of these contaminants in the marine environment. Biomarkers complement the information of the direct chemical characterization of different types of contaminants. Therefore, the role of several biomarkers: (metallothionein
Metallothionein
Metallothionein is a family of cysteine-rich, low molecular weight proteins. They are localized to the membrane of the Golgi apparatus...
s (MT), superoxide dismutase
Superoxide dismutase
Superoxide dismutases are a class of enzymes that catalyze the dismutation of superoxide into oxygen and hydrogen peroxide. As such, they are an important antioxidant defense in nearly all cells exposed to oxygen...
(SOD), catalase
Catalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...
(CAT), glutathione peroxidase
Glutathione peroxidase
Glutathione peroxidase is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage...
s (GPx) (total and selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
-dependent), lipid peroxidation
Lipid peroxidation
Lipid peroxidation refers to the oxidative degradation of lipids. It is the process in which free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage. This process proceeds by a free radical chain reaction mechanism...
(measured as MDA, one of the final products of lipid peroxidation), glutathione S-transferase
Glutathione S-transferase
Enzymes of the glutathione S-transferase family are composed of many cytosolic, mitochondrial, and microsomal proteins. GSTs are present in eukaryotes and in prokaryotes, where they catalyze a variety of reactions and accept endogenous and xenobiotic substrates.GSTs can constitute up to 10% of...
(GST) and acetylcholinesterase
Acetylcholinesterase
"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...
(AChE), were measured in different tissues of the clam Ruditapes decussatus, in laboratory conditions and under various environmental stresses, in two ecosystems (Ria Formosa lagoon, Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
; and Bizerta lagoon, Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
) in a perspective of a multibiomarker approach to assess environmental changes. Experiment and field studies were in good agreement since MT levels, especially in the gills, the first target tissue of these contaminants, can be used as biomarker of exposure to Cd. GPx and MDA may also be determined in this respect. AChE activity is inhibited by pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
and, to a less extent, by metal exposure in the gills and whole soft body of clams. However, the induction of GST isoforms experimentally demonstrated is not observed in the field because only global GST activity was determined. The whole set of results opened new perspectives for the use of this species to assess the effect of mixtures of pollutants in the aquatic environment.