SHRIMPS AND PRAWNS

DR. S.M. ALAM
(feedback@pgeconomist.com)

Aug
22 - 28, 2011

Shrimps are found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can swim rapidly backwards.

Shrimps are important food source for larger animals from fish to whales. They have a high tolerance to toxins in polluted areas and may contribute to high toxin levels in their predators.

Together with prawns, shrimps are widely caught and farmed for human consumption. The prawns have sequentially overlapping body segments (segment one covers the segment two, segment two covers segment three, etc.), chelate (claw like) first three leg pairs, and a very basic larval body type.

The shrimps also have overlapping segments, however, in a different pattern (segment two overlaps segments one and three), only the first two leg pairs are chelate, and they have a more complex larval form.

Biologists distinguish the true shrimp from the true prawn because of the differences in their gill structures. The gill structure is lamellar in shrimp but branching in prawns.

The easiest practical way to separate true shrimps from true prawns is to examine the second abdominal segment. The second segment of a shrimp overlaps both the first and the third segment, while the second segment of a prawn overlaps only the third segment.

While in biological terms shrimps and prawns belong to different suborders of Decapoda. They are very similar in appearance. In commercial farming and fisheries, the terms "shrimp" and "prawn" are often used interchangeably. However, recent aquaculture literature increasingly uses the term "prawn" only or the freshwater forms of palaemonids and "shrimp" for the marine penaeids.

In the United Kingdom, the word "prawn" is more common on menus than "shrimp" while the opposite is the case in North America.

The term prawn is also loosely used to describe any large shrimp, especially those that come 15 (or fewer) to the pound (such as "king prawns", yet sometimes known as "jumbo shrimp"). Australia and some other Commonwealth nations follow this British usage to an even greater extent, using the word "prawn" almost exclusively.

In Britain, very small crustaceans with a brownish shell are called shrimp, and are used to make potted shrimp. They are also used in dishes where they are not the primary ingredient.

Being neither shrimp nor mantids, the Mantis shrimp are marine crustaceans, the members of the order Stomatopoda, receiving their name purely from the physical resemblance to both.

In 2005, it was concluded that they exhibit a similar prey killing dexterity with their claws.

As with other seafood, shrimp is high in calcium, iodine and protein but low in food energy. A shrimp-based meal is also a significant source of cholesterol, from 122 mg to 251 mg per 100 g of shrimp, depending on the method of preparation.

Shrimp consumption however, is considered healthy for the circulatory system because the lack of significant levels of saturated fat in shrimp means that the high cholesterol content in shrimp actually improves the ratio of LDL to HDL cholesterol and lowers triglycerides.

Shrimp and other shellfish are among the most common food allergens. They are not kosher and thus are forbidden in Jewish cuisine. On the other hand, shrimp are halal according to some madh-hib, and therefore are permissible in Islamic cuisine.

Common commercial methods for catching shrimp and prawns include otter trawls, cast nets, seines, shrimp baiting and dip netting. Trawling involves the use of a system of nets. In some parts of the Pacific Northwest, fishing with baited traps is also common.

The following table shows the yearly weight of shrimp and prawns captured globally in millions of tons:

PRODUCTION 1999 2000 2001 2002 2003 2004 2005
Million tons 3.03 3.09 2.96 2.97 3.55 3.54 3.42

The highest rates of incidental catch of non-target species is associated with shrimp trawling. In 1997, the FAO documented the estimated by-catch and discard levels from shrimp fisheries around the world.

They found discard rates as high as 20 pounds for every pound of shrimp, with a world average of 5.7 pounds for every pound of shrimp.

Trawl nets in general, and shrimp trawls in particular, have been identified as sources of mortality for species of finfish and cetaceans. By-catch is often discarded dead or dying by the time it is returned to the sea, and may alter the ecological balance in discarded regions. Worldwide, shrimp trawl fisheries generate about 2 per cent of the world's catch of fish in weight, but result in more than one third of the global by-catch total.

A shrimp farm is an aquaculture business for the cultivation of marine shrimp or prawns for human consumption. Commercial shrimp farming began in the 1970s, and production grew steeply, particularly to match the market demands of the United States, Japan, and Western Europe.

The total global production of farmed shrimp reached more than 1.6 million tonnes in 2003, representing a value of nearly 9 billion U.S. dollars. About 75 per cent of farmed shrimps are produced in Asia, in particular in China, Thailand and in the Philippines (normally shrimps or prawns are caught in lake, river and sea and are not farmed in tanks). The other 25 per cent are produced mainly in Latin America, where Brazil is the largest producer. The largest exporting nation is Thailand.

Shrimps are marketed and commercialized with several issues in mind. Most shrimps are sold frozen and marketed based on their categorization of presentation, grading, colour, and uniformity.

Preparing shrimp for consumption usually involves removing the head, shell, tail, and "sand vein". To de-shell a shrimp, the tail is held while gently removing the shell around the body. The tail can be detached completely at this point, or left attached for presentation purposes.

Shrimps and prawns are versatile ingredients, and often used as an accompaniment to fried rice.

Common methods of preparation include baking, boiling, frying, and grilling. Recipes using shrimp form part of the cuisine of many cultures.

Strictly speaking, dishes containing scampi should be made from the Norway lobster, a shrimp-like crustacean more closely related to the lobster than shrimp, but in some places it is quite common for large shrimp to be used instead.

Wet shrimp is commonly used as a flavoring and as a soup base in Asian cuisines while fried shrimp is popular in North America. In Europe, shrimp is very popular, forming a necessary ingredient in Spanish paella de marisco, Italian cacciucco, Portuguese caldeirada and many other seafood dishes.

Shrimp curry is very popular in South Asia and Southeast Asia. Shrimp are also found in Latin and Caribbean dishes such as enchiladas and coconut shrimp.

Shrimps are also consumed as salad, by frying, with rice, and as shrimp guvec (a dish baked in a clay pot) in the Western and Southern coasts of Turkey.

Most shrimp mature and breed only in a marine habitat, although there are a small number of freshwater species. The females lay 50,000 to 1 million eggs, which hatch after some 24 hours into tiny nauplii.

These nauplii feed on yolk reserves within their body and then undergo a metamorphosis into zoeae. This second larval stage feeds in the wild on algae and after a few days metamorphoses again into the third stage to become myses.

After another three to four-days, they metamorphose a final time into post larvae: young shrimp having all the characteristics of adults.

The whole process takes about 12 days from hatching. In the wild, the marine post larvae then migrate into estuaries, which are rich in nutrients and low in salinity. They grow and eventually migrate back into open waters when they mature. Most adult shrimp are benthic animals living primarily on the sea floor.

Common shrimp species include pink, brown and snapping shrimp. Depending on the species and location, they grow from about 1.2 to 30 centimeters (0.47 to 12 in) long, and live between 1 and 6.5 years.