Difference between shrimp and prawns is probably just in the words. I note in Chinese, the word for prawns and shrimp is the same: "hah" in Cantonese, and "shia" in Mandarin.
In the West, I think prawns refer to the large type, such as Gulf, Tiger and Spot. Shrimp applies to the smaller ones, such as pink shrimp, etc. I guess in the end, the seafood places grade them by the number per pound. I my mind, the giant prawns are about maybe 10-15 per pound.
I found this on the Net:
Coastal MAFES Researches Bigger, Safer Catch
By Rebekah Ray
A different type of agriculture takes place on the Mississippi Gulf Coast.
In an area of the state where land is a premium and population is growing, the Coastal Research and Extension Center (CREC) is looking to readily available water resources for food crop production.
In one project at the Coastal Aquaculture Unit (CAU) in Gulfport, MAFES scientists are conducting novel research in aquaculture, the commercial production of marine fish in a controlled setting.
Additionally, MAFES scientists at the Experimental Seafood Processing Laboratory teach Hazard Analysis Critical Control Point (HACCP) procedures and help processors sustain a safe supply of seafood.
"Seafood research is part of Mississippi State's long-term mission to foster economic development and utilize renewable natural resources. Actually, we're extending the type of research and development that agronomy has practiced for years. We're applying the same techniques to a crop new for the Experiment Station but old to Mississippi," said David Veal, head of CREC.
MAFES researches issues pertinent to the seafood industry at the three coastal centers. Research focuses on processing at the Pascagoula laboratory, on seafood safety in Biloxi and on the growth and harvesting of freshwater prawns and catfish in Gulfpo rt.
"Seafood aquaculture has not been very lucrative yet in Mississippi, but we're researching ways to raise the threshold of earnings for farmers," said Ben Posadas, MAFES marine economist at CREC.
Posadas is conducting experiments at CAU on the culture of larger prawns and on viable partnerships between wetlands and aquaculture.
Prawns. Freshwater prawns usually grow larger than saltwater shrimp. Prawns grow better on pond bottoms and need safe areas to hide during molting seasons when they've discarded their protective shells.
Similar in appearance to shrimp, prawns help lower cholesterol levels and are less prone to diseases. By developing more cost-efficient methods of production, continued MAFES seafood research can develop prawns as a new type of seafood.
"With about three prawn farms, Mississippi produces many small prawns and only a few large ones. Naturally, larger prawns draw greater market prices. We're testing to see how using artificial substrates will increase the weight of prawns," said Posadas.
The crustacean's growth depends on available bottom space. In three of the six research ponds, Posadas installed artificial substrates, or second "bottoms," to evaluate growth rates and weights of prawns. He constructed inexpensive portable substrates by bending plastic mesh into 10-foot waves to increase surface area by 50 percent. The substrates also provided shelter to protect smaller, younger or molting prawns from larger, more aggressive prawns. The other three ponds were the control pa rt of the experiment.
The quarter-acre ponds were stocked with 9,000 45-day old post-larvae (PL) on July 6, 1998, and were harvested November 4 through 6, after 120 culture days. At stocking, each PL weighed .01 gram and was less than one inch long.
Prawns were fed twice daily with 32 percent "sinking" catfish feed, based on the feeding schedule determined by MAFES scientists at the MSU Leveck Animal Research Center in Starkville. Dissolved oxygen and temperature were monitored daily, wh ile total ammonia, nitrites, salinity and pH were measured bi-weekly for management purposes.
Substrates were removed before prawns were harvested in early October.
To harvest, researchers seined the ponds by stretching a net from side to side across the pond to filter water through it as they walked the length of the water. Then the pond was "scrapped," which included draining the water so researchers c ould wade through the mud to manually harvest prawns hidden in crevices and low spots.
Harvested weight was 17 prawns per pound at an average weight of 26 grams each. Ponds with substrates yielded 347 lb/pond, or 1,388 lb/acre, while ponds without substrates yielded 291 lb/pond, or 1,164 lb/acre.
"This is good. We had been shooting for at least 125 pounds per pond, and we harvested more than 300 pounds per quarter-acre pond. I had been hoping for 300 pounds of prawn from the subscreened ponds," said Posadas.
Although the results of using substrates were positive, several problems appeared, such as predators and costs of substrates.
Predators including cormorants, raccoons and snakes accounted for some loss of the product.
Also, substrates may not be financially feasible for farmers.
"We need to compare the added costs of substrates to the increase in revenues." Posadas said.
"Building the 10-by-200 foot substrate was rather labor intensive. Six people built and installed the screen so another type of substrate may be tested next year," Posadas said.
Another problem included the approach of cooler weather. The growing season for Macrobrachium rosenbergi is mid-May to the first of November. Prawns die when water temperature drops to 60 degrees Fahrenheit.
"If we could have left them in the water for another 30 days, we might have hit 12 prawns per pound, but we had to harvest now because the water was getting too cold for this species," said Posadas.
In spite of these problems, results were good.
"Our numbers were great. They're better than we had anticipated," Posadas said.
Part of the harvesting process included sorting prawns by size as well as by sex. Harvesting at this point in species development, females were more easily detected because of their large orange egg sacks.
Crustacean research in seafood aquaculture is significant. Between 75 and 80 percent of shrimp are imported to this country from Central America and Southeast Asia. About 100 species of shrimp are traded worldwide.
Saltwater shrimp aquaculture in Asia and the Americas had been beset with disease problems.
Shrimp diseases include Taura Syndrome Virus, White Spot Virus, and Yellow Head Virus. These affect cultivation numbers. Chances are great that prawns bought in grocery stores have been infected with one of these viruses, but the viruses have no effect on humans.
"Although we can't really compete with the lower labor costs in these countries, we can produce a higher quality product. Strict requirements and regulations set by the Food and Drug Administration, Environmental Protection Agency and other federa l and state regulatory agencies help keep our fish clean and disease-free," Posadas said.
Another plus for raising farm-produced shrimp and prawns includes using animal byproducts as animal foods and fish oils.
"Freshwater shrimp farming has not yet taken off in Mississippi, but there is a renewed interest. It surely holds regional promise," Posadas said.
Wetlands. In addition to its research ponds, the CAU has 13 wetlands adjacent to its experimental ponds that are the focus of another major research effort.
Wetlands are areas covered by water, or where water is present either at or near the surface of the soil all year or for varying periods of time during the year, including the growing season. Water saturation is a major component in soil development an d the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species.
Wetlands are categorized as coastal or tidal wetlands and inland or nontidal wetlands. Tidal wetlands are located along the Atlantic, Pacific, Alaskan and Gulf coasts, and are closely linked to estuaries, where seawater mixes with fresh water. Inland w etlands are commonly found on floodplains along rivers and streams.
Posadas is investigating the use of constructed wetlands to improve water quality from aquaculture ponds. Poor water quality in catfish production ponds can lead to the direct loss of fish and cause off-flavor problems in the harvested product. Circula ting pond water through constructed wetlands helps clean the pond water, improves yield, reduces mortality and alleviates off-flavor in catfish.
The project tested use of a standard design for the pond-wetland system and evaluated variations in the design factors, such as size and flow rates of water through the wetlands.
In the ongoing projects, six quarter-acre ponds were stocked with 10,000 catfish per acre in May. Six additional quarter-acre ponds were stocked with 8,000 catfish fingerlings per acre in April.
Results of catfish yields for ponds with wetlands were about the same as for ponds without wetlands. Measuring the effect of using wetlands in conjunction with catfish ponds was difficult because predators such as cormorants could not be isolated, so e xpected levels of yield, anticipated revenues, mortality rates and off-flavor were not realized.
Constructed in 1987, CAU is located on the grounds of Mississippi Power Company's Plant Jack Watson in Gulfport. The center consists of a 2,200-square-foot research facility and 26 one-quarter acre research ponds for aquacultural, water quality, wetlan d and estuarine-related research. The facility has also conducted research in nutrition, stocking densities, disease reduction, breeding habits, genetics, cage culture and the quality of wetland water. Aquaculture research has been conducted at the center since its inception.
Sustained Seafood Safety. MAFES scientists ensure the sustained safety of processing seafood by updating processors on safer methods for improving and maintaining the quality of the seafood products.
"We're working to sustain a safe, wholesome supply of seafood available, while at the same time, extend the shelf life of what's being harvested," said Custy Fernandes, MAFES food fisheries scientist.
Fernandes and MAFES food scientists Doug Marshall and Juan Silva teach HACCP methods to seafood processors.
Along its coast, Mississippi has more than 100 seafood companies that process primarily shrimp, oysters and crabs. HACCP includes identifying hazards at each processing operation and identifying critical control points (CCP) to monitor, eliminate and r educe biological, chemical and physical hazards. Critical limits are established at each identified CCP where processors monitor activities and use corrective action to return the process to normal.
Since December 1997, seafood production and the aquaculture processing industry have followed HACCP regulations for better management of processing facilities. Using a system of checks and balances, processors provide regulators with records to verify safety of products.
Fernandes updates local and state seafood processing companies by providing guidance in their HACCP program. Currently, he serves on the sanitation standard operating procedures (SSOP) technical committee of the National Seafood Alliance. The goal of t he National Seafood Alliance is to develop a national and international curriculum for SSOP.
MAFES research looks at the microbial quality of seafood before and after the implementation of HACCP to see if treatments have been effective. Research has shown that seafood microbial quality has been sustained because processors follow good manufact uring practices (GMP) and SSOP. These procedures avert temperature abuse, reduce levels of microbial spoilage and extend shelf life.
During harvesting, shrimp may develop melanosis, or black spots, from biochemical reactions and become "cooked" on the boat deck. Although these "Halloween shrimp" are harmless, black and orange shrimp reduce quality and the shrimp never make it to the market.
To preserve the quality, shrimp are treated with the preservative NaHSO3, or sodium bisulfite, a preservative generally regarded as safe. While still on deck, the seafood is iced down. Harvested shrimp are soaked or immersed in NaHS03, a common practice.
Economic Impact. Built on the harvesting and processing of oysters, Biloxi was once nationally known as a seafood processor and claimed to be the Seafood Capital of the World. Presently, money may be rolling in from increased tourism, but the co mmunity is losing its leadership role in the seafood industry because of labor losses and man-made intrusions on the environment.
Fernandes is researching how this change is affecting Biloxi's seafood industry, particularly the mechanization of shucking oysters. His research evaluates a freeze-and-heat method of facilitating oyster shucking.
MAFES aquacultural research is paving the way for Mississippi to become a leader in the seafood industry.
mafes.msstate.edu
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