Lawson Wood answers the question -are shrimps and
prawns the same species?
Photographs by Lawson Wood
I get asked this question lots of times by fellow divers, amateur marine biologists, photographers and even chefs! I had been led to believe that a shrimp was just a small prawn! However, shrimps and prawns are two fundamentally different creatures. Both are decapods having external skeletons, ten legs and kind of look the same. That’s where the similarity ends. Shrimps are members of the sub-order Pleocyemata, and prawns belong to the sub-order Dendrobrachiata.
Anatomical Differences: Shrimp vs. Prawn
Simply put, shrimps have one pair of legs which have claws at the ends and prawns have two or three pairs of legs bearing claws, and these legs are generally longer than shrimps in relation to the body size, with shrimps having legs approximately the same size as their bodies.
Other anatomical differences include the fact that shrimps have a type of ‘accordion’ shell where the body is made up of segments which have a membrane between each segment; prawns on the other hand have overlapping bony plates making them less flexible.
The gills of shrimp are known as lamellar or plate-like and the gills on prawns are branching.
Reproductive and Habitat Differences
Shrimps carry their eggs on the underside of their bodies after they have been fertilized, whereas prawns release their fertilized eggs into the water column, where they start life in the plankton before settling onto any suitable habitat.
In British waters, the biggest critter is the langoustine, sometimes called the Norwegian lobster (Nephrops norvegicus). This prawn is more similar in shape (and sometimes) size and are usually a bright orange in colour.
These prawns are commercially harvested and were once captured as bycatch and sometimes discarded, but now the commercial industry around these delicacies is massive, with most of the catch being exported to France and Spain.
Italy has its own source of langoustine, which are caught in the Adriatic. Fishing methods have changed thankfully, and these large prawns are no longer caught by dragging fishing gear along the seabed, now most langoustine are caught in modified lobster/crab pots.
More notably from the Scottish west coast, they are easily found in Loch Fyne, Loch Leven and many other Scottish sea lochs, as well as all along the North Sea coasts.
The langoustine also has a very similar existence to those shrimp gobies found in more tropical waters, where the crustacean has a symbiotic relationship with a goby.
Here in UK waters, this large prawn has a partner with the Frie’s goby (Lesueurigobius friesii), which sits as a sentinel outside the prawn’s burrow and darts inside as a warning to the prawn should danger threaten. This danger is namely from thornback rays, lesser-spotted dogfish and spurdogs.
Common UK Shrimps and Prawns
There are several species of shrimps and prawns in UK waters, some are commercially harvested like the common or brown shrimps in the Wash area of East Anglia. Crangon crangon is regarded as a true shrimp and usually grows to over 50mm and is commercially harvested in East Anglia and the Baltic states.
It has a wide distribution and is also found throughout the Mediterranean and is usually located in shallower water on sand.
Bearing one pair of short but fairly stout claws, this shrimp has a much more flattened body than a prawn, making itself easier to hide under the sand should danger threaten. This was the first shrimp to be categorised in 1758 by Carl Linnaeus.
Our most-common species is the common prawn (Palaemon serratus), which is characteristically translucent with pink to red vertical stripes over the carapace and flanks of the tail.
Its back is quite straight, but with a slight ridge, and its legs have very obvious yellow bands at each of the joints as well as sometimes also having blue markings. The main, long antennae are striped and the front two pairs of legs have small pincers which it uses to pick up and hold food morsels whilst it feeds.
This prawn is often found at the entrances to small caverns usually occupied by much larger squat lobster, lobster and even conger eels and ling. This was the first prawn to be categorised in 1777 by Thomas Pennant.
Almost identical is the elegant prawn (Palaemon elegans). Sometimes referred to as the rockpool prawn, it is common around all of our shores and yes, as the name would suggest, this is the species most usually found in our rockpools as it is able to adapt to both increased temperatures and salinity, particularly during the summer months when sun, evaporation or rain can drastically change the salinity or temperature of the water in a shallow rockpool.
This species is also translucent with faint brownish stripes over all of its body, but does not have the identifying yellow or blue bands on its legs.
In more northern waters the Aesop, humpback, pink or northern prawn (Pandalus montagui) is an attractive prawn, mainly transparent, but with pink or red patches and more diagonal stripes all over the carapace and along the sides of its body.
The southern channel coast was thought to be its most-southerly range, but it has been seen in France and northern Spain. Similar to its more-tropical counterparts, the northern prawn has a symbiotic relationship with the pink anemone (Bolocera tuediae) and can usually be found sheltering under the outer ring of the anemone’s tentacles.
Inshore around our rocky reefs there are a fair number of other species. The long-spine or peppermint shrimp (Hippolyte longirostris) is well named as its rostrum is almost as long as the carapace and usually comes in a variety of camouflage colours, but it does have tiny iridescent blue spots over its body, making it quite distinctive.
Another more common shrimp is the white-stripe shrimp (Hippolyte inermis) which is usually at home on kelp fronds. Growing to around 50mm, it is mainly a greenish brown in colour with a very obvious white strip which stretches the entire length of the body.
Iridescent blue spots can also be found on this species. Once thought to be quite scarce it can be found on the African coast of Morocco, all the way through the Mediterranean and into the Black Sea.
The chameleon prawn (Hippolyte inermis) is another one to argue over, as this species is actually a shrimp! Growing to over 25mm, as the name suggests this little critter is very variable in colour, often having every colour, but what makes this one stand out is that the body can have small tufts of setae on the body, further allowing it to blend in with its surroundings.
Hippolyte leptocerus is a new one for my list, I had seen this species for many years, but failed to get any good photographs, but this last year I have found it in a number of locations in sout east Scotland on a number of different habitats, such as dead man’s fingers and various seaweeds.
It is small and usually around 20mm, translucent but with a very obvious dark red stripe above and below the body, making it very difficult to spot. My great friend Dan Bolt has also photographed this species off Cornwall.
A much smaller and rarer shrimp is the occult shrimp (Eualus occultus), usually hiding among dead man’s fingers in more northern waters, but is equally at home around Devon and Cornwall and even the Mediterranean.
It has a pointed rostrum and an arched back. Being semitransparent, its newly fertilized eggs are first stored within the head cavity and once released, the female carries the egg brood between her swimmerets under the main part of the abdomen, further raising its back even more.
Misidentified and Lesser-Known Species
Finally, just to confuse us even more are another couple of critters which are commonly called shrimp, but are certainly not! The first is the opposum shrimp (Leptomysis gracilis) which occur in large numbers usually in deeper waters around our shores, where there is little or no current.
Free swimming, they vaguely resemble little shrimps, they have a large head tapering off to a rather pointed tail.
Difficult to tell apart is Paramysis helleri, also found in abundance in sheltered corners. These 12mm little critters are crustaceans and members of the order Mysidacea. There are over a 1,000 species worldwide and their names derives from the fact that their eggs are held in a brood pouch on the abdomen, similar to marsupials.
The other is the skeleton or ghost shrimp (Caprella linearis) – also nowhere near being a member of the shrimply sub-order, as this critter is actually an amphipod and a member of the Caprellidae family.
These are also usually found in large numbers, often covering dead man’s fingers and various type of hydroids which tend to be out in the current and able to catch any drifting plankton.
This crustacean hooks onto its host by its rear appendages and stretches out from its host into the current. It has a cylindrical body, almost skeleton-like, large antennae and two large pincer-like appendages, but only grows to around 12mm.
Global Perspective and Culinary Confusion
As far as chefs are concerned shrimps and prawns pretty well all taste the same once fried in garlic butter or whatever, as mentioned earlier, I had been led to believe many years ago that it was all to do with size! Shrimps were small, whereas prawns were much larger.
Fundamentally that is correct, but hardly accounts for juvenile prawns or very large shrimps which could, of course, be one species or the other.
However, just to add things into the mix, virtually 70% of all commercially harvested (restaurant) species are prawns which come from the marine aquaculture farms in Asia or Latin America.
But in the United States, no matter where these prawns come from, Americans only ever call these prawns shrimp! They now call king prawns jumbo shrimp!
Globally, there are around 3,000 species of prawns and the two species which we eat most in restaurants, fastfood franchises and supermarkets account for 70% of the $25bn that we spend each year for around ten million tons (live weight) of commercially harvested prawns.
This massive industry is thought to employ over two million people worldwide. Curiously, the term ‘prawn’ now appears to be for fresh warm-water harvested species and the term ‘shrimp’ is now reserved for salt water commercially harvested species. Even though langoustine or scampi are actually prawns.
The other exception to this rule is the species of coldwater prawns which are harvested from the wild in Arctic waters, namely Greenland; Iceland and Norway.
This is the Arctic prawn (Pandalus borealis) of which some 300,000 tons are harvested each year and it is this species which we find most of on the supermarket shelves (advertised as coldwater North Atlantic prawns.
Only caught in the wild and totally organic, it takes around five years for this little prawn to gain around 10 grams, whereas farmed prawns from Asia gain around 30 grams in under a year! Please remember that those with allergies, shrimps or prawns will have the same adverse effect.
I am not sure what the conclusion is on the question whether any particular critter is a shrimp or a small prawn. They are two different family groups, but depending on where you come from or where you eat, will depend on what you call them! The rest is a mystery!
This article was originally published in Scuba Diver UK #79
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