Is Scallop a fish?

In this post, we will answer the question “Is Scallop a fish?”, outline and discuss Scallop biology and ecology.  

Is Scallop a fish?

No, a Scallop is not a fish. Scallops are bivalve molluscs that belong to the Pectinoidae family and the Pectinoida order. These molluscs inhabit marine waters inside shells of irregular and varied shapes. These shells are calcified and remain closed due to an adductor muscle. These animals are closely related to oysters and mussels.

Bivalves

Bivalvia is one of the classes of the Mollusca phylum. Bivalves are animals whose bodies are protected by a shell composed of two valves. They are mostly marine animals, but they also exist in freshwater environments. 

It is from the bivalves that the pearls come from. These animals can filter the water. The water filtered by some molluscs can bring impurities (sand, rocks, pieces of shells, etc.), these become trapped between the mantle and the shell and it is enveloped by secretion and after years of accumulation, it turns into a pearl.

We will now learn more about this animals biology and its specificities:

–       Gas exchange;

–       Food; 

–       Digestive System;

–       Circulatory system;

–       Excretory system;

–       Nervous system;

–       Reproduction;

–       Systematics;

–       Geological history.

Gas exchange

The gas exchange of bivalves is carried out through the gills and also through the mantle. The bivalve’s gills are composed of long filaments folded to form the lamellae. The water enters through the siphon (the organ that internalizes and externalizes water), passes through the pores between the filaments of the lamella and then to a chamber called suprabranchial, and leave the body. During this route, the gas exchange occurs, from the filaments to the water and vice-versa.

Food 

Bivalves are typically filter feeders, they feed on suspended organic particles in the water that enters through the siphon and are directed by cilia to the gills so that the filtration can occur. 

After the filtration, the particles are directed to the labial palps that transport them to the mouth. Some species feed on wood and are associated with bacteria that digest cellulose. Others use the siphon to search the sand for food. And some suck small animals into the mantle.

Digestive System

The stomach of filter feeders has several folds and the entire path is ciliated. There is a digestive chamber that produces enzymes and dumps them into the stomach. Bivalves undergo intra- and extracellular digestion.

Circulatory system

The heart of the bivalves has three chambers, two atria and one ventricle. As the gas exchange is also carried out through the mantle, part of the blood receives its oxygenation in this tissue and then returns to the lung and other body parts.

Excretory system

Bivalves excreta are filtered by two kidneys. The tubules of the kidneys open in the pericardium and then into the suprabranchial chamber.

Nervous system

The nervous system of bivalves is made up of three ganglia connected by nerves. Sensory organs are not very developed. Some of them are tactile sensing cells, an eye on each side of the mantle, tentacles and some chemoreceptor cells.

Reproduction

The bivalve gametes are accumulated in the suprabranchial chamber and then carried out by the water flow for external fertilization. 

Development is indirect, they pass through larval stages of trochophore and veliger larvae. Freshwater bivalves usually have internal fertilization. Eggs go to the pores of the gills where they are fertilized. The larvae from this process settle in fish, living as parasites.

Systematics

Bivalvia Class is composed of 5 subclasses and 17 Orders:

–       Arcoida (6 families);

–       Euheterodonta (4 families);

–       Limoida (1 family);

–       Myoida (4 families);

–       Mytiloida (2 families);

–       Ostreoida (9 families);

–       Pholadomyoida (13 families);

–       Pterioida (5 families);

–       Veneroida (35 families);

–       Carditoisda (1 family);

–       Hippuritoida (5 families);

–       Nuculooida (5 families);

–       Pectinida (1 family);

–       Solemyoidea (1 family);

–       Trigonioida (1 family);

–       Unionoida (2 families);

The Bivalvia class has marine, brackish, and freshwater species. Myoida order has species with well-developed siphons to burrow themselves into the substrate.

Geological history

Bivalves emerged in the Cambrian, about 500 million years ago, in the marine environment and became more common in the Silurian. The first forms of freshwater arose in the Lower Devonian. Thus, some groups helped to define the stratigraphy of Carboniferous coal deposits. Bivalves suffered a marked reduction in the permo-Triassic extinction. However, the groups that survived quickly recolonized the diverse ecological niches.

The biology of the Scallop

Scallops are marine bivalve molluscs of the Pectinidae family. This family has more than 300 extant species divided into 60 genera. They are found in several oceans and abundantly in North America, northern Europe, and Japan, where they are highly appreciated as refined food. 

In France, they are the famous coquille saint-Jacques. Collectors and malacologists admire the fan-shaped colourful shells of some Scallop species. It is also the shell portrayed in Botticelli’s The Birth of Venus. Their most interesting feature is that they are active swimmers, being the only migratory bivalve, moving by propulsion with the help of the adductor muscle.

Anatomy of Scallops

Similarly to the true oysters (family Ostreidae), Scallops have a central adductor muscle. This muscle attachment mark is visible inside their shells when opened. In Scallops, the adductor muscle is stronger and bigger than the one of oysters. As they are active swimmers, Scallops are the only migratory bivalve individuals. 

The shape of their shells tends to be highly regular, the archetypal shape of a shell, and because of its harmonious geometry. Their shells often have a decorative pattern. Scallops have eyes with lenses and retina, which are more complex than those found in other bivalves. Although they cannot see shapes, they can detect light and movement.

Food and life habits

Scallops feed by filtering plankton. Occasionally, plankton may include scallop larvae. They do not have siphons. Thus, the particles of food are trapped in mucus. Then the lashes on the structure move the food towards the mouth, this structure is called cilia. Food is digested in their stomach. Then it passes through the intestine for absorption and out through the anus.

Most scallops are nomadic, which means they have great migratory characteristics and are classified as free-living organisms. However, some species can be fixed to a substrate by a structure called a byssus. A free-living, swimmer scallop can move around very fast by the opening movement of its shells. This method of locomotion is also a defensive technique, protecting them from predators. There are some scallops known as the “singing scallops”, they can make a soft but audible popping sound as they tap the shells underwater.

Scallops in the gastronomy

Scallops are considered to be the most sensitive cousins of oysters as they resist very little time out of the water. This makes them be sold frozen and considered a highly sophisticated product.

Scallops can be used in many different dishes. In addition, they have a sweet flavour, in contrast to other seafood. With them, it is possible to prepare elaborate recipes, such as risottos or even simpler ones, such as puree.

Scallops have more sensitive meat and must be eaten fresh. To choose correctly, they cannot have a strong odour and the shells need to be well closed.

Importance of scallops

These animals are filter-feeding species that help to maintain aquatic environments and provide better conditions in tanks and other environments.

In addition, bivalves are an important source of food for fish, birds, and people. Their shells are also used to make jewellery and crafts in various regions around the world.

Conclusion 

In this post, we answered the question “Is Scallops a fish?” We also outlined and discussed Scallop biology and ecology.  

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): IS Scallop a fish?

Are Bivalves molluscs?

Yes, Bivalves are molluscs. Bivalves are animals that have a shell made up of two valves. They belong to the group of molluscs. There are about 8 thousand (8,000!) species of bivalves. This group includes scallops, clams, mussels, oysters, vongoles, and various other types of seafood.

How do scallops burrow themselves?

Many bivalve species are sessile. However, some can burrow into the sand using their feet. The sessile species can synthesize strong threads that guarantee their fixation to the substrate, such as rocks and boats.

How do we eat the Scallop dish?

The scallop is a white meat mollusc with two fan-shaped shells. Scallop meat has a firmer consistency in comparison to other molluscs, such as oysters, and is well grilled or au gratin.

Does Stingray taste like Scallops?

Yes. Stingrays are also known to taste similarly to scallops and oysters. However, some people think they taste more like sharks.

Can you eat raw scallop?

They can be made raw, blown, or quickly sealed. You cannot cook or fry them for a long time, as they lose flavour, juiciness and texture.

What is the bivalve adductor muscle for?

The adductor muscles connect the left and right valves. In addition, the adductor muscle helps the animal to keep the valves closed, and, when necessary, the adductor muscles helps with opening and moving around.

Why are Scallops bad for you?

Scallops are known to be filters. Thus, they can accumulate high amounts of heavy metals, such as mercury and lead. If consumed in frequency, the heavy metals concentration in the human body can cause cancer and other health issues.

References 

Shumway, S. E., & Parsons, G. J. (Eds.). (2016). Scallops: biology, ecology, aquaculture, and fisheries. Elsevier.

Shumway, S. E., & Parsons, G. J. G. (Eds.). (2011). Scallops: biology, ecology and aquaculture. Elsevier.

Beninger, P. G., & Le Pennec, M. (2006). Structure and function in scallops. In Developments in aquaculture and fisheries science (Vol. 35, pp. 123-227). Elsevier.

Gosling, E. (2008). Bivalve molluscs: biology, ecology and culture. John Wiley & Sons.

Coan, E. V., Scott, P. V., & Bernard, F. R. (2000). Bivalve seashells of western North America. Santa Barbara Museum of Natural History Monographs, 2, 1-764.

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