Types of Shellfish
Shellfish is a term used to describe aquatic invertebrates (having no backbone). These invertebrates also have an exoskeleton meaning that their skeleton is on the outside not the inside like ours. Details of how each of these animals grow is given for each species.
Most types of shellfish are a highly prized seafood, especially lobster.
Family – Nephropidae
Breeding Time – Mainly summer
Availability – Less in winter
Lobsters grow by shedding their shells (molting) and the soft shell underneath then hardens over a period of about a month. A lobster will shed up to 25 shells by the time it is 5 years old but this will slow down to one every one or two years.
Lobsters can live a long time and older lobsters get very big in size. A lobster that is not in pristine condition and has a few barnacles should not be discarded as they usually produce more meat. It is advisable to secure a lobsters claws when they are being kept in tanks as they will fight each other and actually eat their fellow lobsters.
Family – Cancridae
Breeding Time – Winter
Availability – Most in summer
As with lobsters, crabs also shed their shells in order to grow. The crab is vulnerable while the soft shell is hardening – over a period of about a month. Crabs known as soft shells are those that have just shed their shell.
The brown crab is the most common edible crab in UK waters. Velvet crabs and spider crabs are also caught but most are exported to the Continent. The brown crab is mainly caught in baited pots. The brown crab is a reddy brown colour and has black tips on the end of it’s claws.
Brown crabs can grow up to about 3kg in weight.
Family – Mollusca
Breeding Time – Spring and summer
Availability – Farmed readily available
As mussels remain in the same spot for their entire lives, they just cling on and gradually get larger. You can see the growth rings on the shell in the same way that you can see rings on a tree. Mussel live around 10 years.
Mussels are readily available in the UK and are often farmed. They cling on to a rock or rope such as a mooring line using their ‘beards’. These beards are actually strong byssal threads. The mussels remain in the same spot for their entire life. It is not a good idea to harvest your own mussels unless you know that the water they are living in is not contaminated as mussels are filter feeders and will pick up anything nasty in the water.
Farmed mussels tend to have thinner shells as they live in sheltered water and haven’t had to protect themselves from currents. Farmed mussels also tend to have more meat as they are fed constantly whereas mussels in the sea have periods when the tide is out and feeding can not take place.
Some people say that you should not buy mussels when there is an ‘R’ in the month. This is because the summer months are when spawning takes place so the meat tends to be less at this time.
Family – Pectinidae
Breeding Time – Warmer months
Availability – More in winter
Scallops keep the same shell all their lives and this just carries on growing. It is possible to tell the age of a scallop by looking at the concentric rings (the annuli) on the shell. Scallops reach a harvestable size in about 6 years and can live until they are 18
Scallops have tiny eyes around the edge of their mantles and they use these to detect predators. While they are unable to define actual shapes they can use them to determine light and dark such as the shadow of an approaching predator.
Scallops live on the bottom of the sea and bury themselves in the sand. Some will attach themselves to rocks in much the same way as a mussel but most scallops will be free moving. They are able to swim rapidly by opening and closing their shells.
Scallops are highly prized food and are quite expensive to buy.
Family – Ostreidae
Breeding Time – May to August
Availability – Sept to April Only
Native oysters to the UK take about 4 years to grow to a size that is marketable which is much slower than the Portuguese or Pacific varieties.
There are two types of oyster available in the UK. The native oyster and the Pacific oyster. Pacific oysters grow much more quickly than native oysters and were introduced in the 1960s following a decline in the quantities of native oysters. Oysters are often eaten raw with just a squeeze of lemon.
Oysters have allegedly got aphrodisiacal qualities.
Shrimps & Prawn
Family – Crangonidae
Breeding Time – Spring
Availability – Summer Months
Shrimps and Prawns shed their shells much like crabs and lobsters in order to grow.
The jury is out on what the difference is between a prawn and a shrimp and if anybody could let us know the definitive answer we’d be very grateful! The main consensus seems to be that in the UK ‘prawn’ is the common name and in the US ‘shrimp’ is. Prawns are also than shrimps but we are afraid we do not know at what size a shrimp becomes a prawn.
Both species are the same as lobsters and crabs in that they are decapod crustaceans – this means that they have 10 legs and a hard shell. However unlike lobsters and crabs who crawl along the bottom, shrimps and prawns both swim around.