To most people the words ‘prawn’ and ‘shrimp’ mean something deliciously edible from the sea, probably with several legs and a hard shell. Australians think of prawns as large animals seen in the fish shop or on the menu in a restaurant. To them shrimps are smaller, the little pink things on the top of pizzas or maybe the small quick translucent creatures in rock pools.
But it isn’t quite that simple.
Prawns and shrimps are decapod Crustacea
Before deciding if prawns and shrimps are different, it has to be agreed that they are at least a bit similar. All prawns and shrimps are crustaceans, which are mostly aquatic animals with a hard skin (an exoskeleton) over a segmented body. Crustaceans belong to the subphylum Crustacea. They are like insects, which also have an exoskeleton, but differ in usually having many pairs of legs, instead of three pairs. The Decapoda, the group of Crustacea to which all prawns and shrimps (and lobsters and crabs) belong, have five pairs of legs on the main part of the body, plus five pairs of swimmerets on the abdomen or tail. It is the muscular tail that is edible. The classification of the Decapoda is very complex, even to a carcinologist (a scientist who studies Crustacea).
The crustaceans that Australians call prawns belong to one decapod family, Penaeidae. Adults grow to about 200 mm long. Most penaeids sold in Australian fish shops are caught by trawlers in the tropics, in places like the Gulf of Carpentaria. Small fisheries for prawns exist in estuaries farther south. In Asia prawns are raised in coastal farms.
Penaeids live close to the seafloor in shallow water, burrowing in the mud during the day and moving only at night, when they can be caught by trawl nets. Prawns reproduce by dispersing their eggs freely into the water, where the young prawns hatch and swim into estuaries to grow up.
There are about 70 species of prawns in Australia, but only 10 are of economic significance: banana prawn, Endeavour prawn, tiger prawn, king prawn, red-spot prawn and school prawn are some of the names used for different species or groups of species.
Australian shrimps, on the other hand, are members of the Caridea, another group of Decapoda comprising many families. Most carideans are not edible, or they are too small (rarely more than 40 mm long) to be caught commercially in Australia. The only edible shrimps seen in Australia are imported in cans from Asia. Carideans produce eggs that are carried by the adult female, attached to the swimmerets under the tail.
Photographer: Michael Marmach. Source: Museum Victoria
A typical shrimp
Illustration: Jo Taylor. Source: Museum Victoria
Telling shrimps and prawns apart
An important difference between penaeids and carideans, besides the way they reproduce, is in the way the segments of the abdomen (tail) overlap. In penaeids (prawns) the sides of all segments overlap the segment behind, like roof tiles. In carideans (shrimps) the sides of the second segment overlap both the one before and the one after (see drawing). And in prawns the first three of the five pairs of legs on the body have small pincers, while in shrimps only two pairs are claw-like. In some shrimps one or other of the first two pairs of legs is bigger than the other whereas in prawns all the legs are similar lengths.
A shrimp in the USA is a prawn in Australia!
But that is not the end of the story. There is a large fishery for penaeids in the southern USA, especially in the Gulf of Mexico, and Americans call them shrimp! Paul Hogan made the word familiar in Australia with his expression ‘Throw another shrimp on the barbie!’
A typical prawn
Illustration: Jo Taylor / Source: Museum Victoria
Grey, D. L., Dall, W. and Baker, A., 1983. A Guide to the Australian Penaeid Prawns. Northern Territory Government Printing Office: Darwin.
Poore, G.C.B. 2004. Marine decapod Crustacea of southern Australia. A guide to identification (with chapter on Stomatopoda by Shane Ahyong). CSIRO Publishing: Melbourne.