In culinary terms, when we buy shrimps or prawns from the fishmonger or supermarket or order prawns or shrimps from a restaurant menu we generally differentiate simply on size. Smaller species we call shrimps and larger species we call prawns. Just to add to the confusion, the terminology can differ from country to country. What the British call a prawn could well be called a shrimp on a US or French restaurant menu.
So how do we really tell the difference between these two crustaceans?
Prawns and shrimps are very similar in appearance, each having ten legs and each has many varieties and is found in nearly every part of the world’s oceans. Counting shrimps and prawns together, there are over three thousand different species . Both shrimps and prawns start their lives as male and then change to female for the final phase of their lives. To add to the confusion, when they are cooked they taste pretty much the same – although as a rule of thumb you could say that the smaller varieties tend to taste rather sweeter than their larger cousins and that cold water shrimps and prawns are generally firmer in flesh and of higher quality than warm water varieties.
In biological terms, the shrimp comes from the sub-species Pleocyemata and the prawn from the sub-species Dendobranchiata. The most obvious difference is in the structure of the gills. Prawn gillshave a lamellar (plate like) structure, while shrimp gillshave a branch like structure. The legs of a prawn are longer in relation to its body size than those of a shrimp If you were to enlarge a prawn you would find it looked more similar to a lobster, with its two pairs of pincers than to a shrimp.
As this article is primarily aimed at the culinary reader, we can say that in practical terms, once a prawn has been cooked, denuded of its shell and prepared for the plate it is pretty much indistinguishable from a shrimp. The good news is that shrimps and prawns are equally versatile in cooking. The not-so-good news is that each is quite high in cholesterol, and should not be eaten more than once a week by the 25 percent of the population whose bodies are prone to absorbing excess cholesterol in their diet.
Just one more thing to confuse you a little further; Dublin Bay prawns are neither prawns nor shrimps. They are langoustines. But that is for another day.