Growing Oysters Reading Answers

Oysters have been farmed since Roman times, and in many areas approaches are much the same as they were back then, because they still work. However, there has also been quite a leap in farming methods, which has allowed oysters to be farmed much more efficiently or in areas where it would not have been possible before. Baby oyster seeds are obtained by farms from hatcheries each spring. The seed is only about 1 millimeter in length and is packed in a very fine mesh enclosure. The seeds look like small pepper flakes when they arrive, and they are placed in floating upwellers, where the tiny oyster babies are in a protected environment. Here they can feed and grow on nutrient rich water.

Pumps push water up and over the oysters in small silos, so they constantly receive a fresh supply of phytoplankton. The baby oysters remove excess nitrogen and carbon based nutrients from the water, thereby improving water quality and clarity in a nitrogen and carbon negative process. Oysters, like any animal, grow at diverse rates, so the fast growers must be separated from the slow growers. Once the oyster seeds are large enough, they are moved out of the upwellers and placed in mesh bags contained in floating cages, so they can feed in the water column and avoid being smothered by sedimentation.

From time to time, oysters must be placed in an oyster tumbler, which grades them according to size, washes them, and chips off the leading edge of the shell to give the oyster the characteristic cup appearance over time. Simultaneously, the oysters are divided into roughly double the number of cages, thereby increasing the amount of water flow and decreasing the competition for sustenance within the cage. These processes are repeated every 4 weeks throughout the summer and fall. Because of the colder temperatures and lower salinity of winter water, the oysters slow down their feeding and growth and eventually they enter a state of dormancy. During winter, the tumbling and dividing process is stopped and the cages are simply monitored to ensure they remain in good condition. Once the water temperatures and salinity begin to increase, the oysters wake up and begin feeding and the tumbling and the dividing process begins again. Once the oysters reach approximately 2 inches in size, they are placed in cages in more open water, where the wave action will toughen them up and strengthen their abductor muscles. This prepares the oysters for shipment.

After approximately 18 months, the oysters are tough enough and are ready for harvest. The oysters that are ready are washed down, bagged up and placed in boxes if they are being shipped directly. They are then taken away for shipment. The suitability of growing areas for oysters can be evaluated by the amount and type of pollutants in the various growing areas. Oyster banks should not be exposed to strong currents or wave action under normal tidal conditions or during times of flood. Areas that are prone to shifting sand and can also be problematic. These adverse conditions place additional stress on the oyster growing furniture, damage oysters, and make working in These areas are difficult. Some balance must be struck between currents and tidal flows to ensure that they supply the oysters with suitable water that is a nutrient-rich food source. Open water also leaves the oysters vulnerable to small fish predation, which can have a serious effect on production yields. The substrate should be firm enough to walk over, and to work on, although this is not always the case. Offshore areas may be problematic if they are not close to a suitable land-based facility and long distances must be traveled each time stock is to be placed or maintenance carried out. Access to markets also needs to be considered, particularly when moving oysters to be processed.

Estuary systems are particularly good at producing the populations of phytoplankton that oysters predominantly feed on. As oysters are filter feeders, the selection of maturing grounds is very important to avoid possible contamination. Commercial oyster culture all over the world is managed under stringent eco-guidelines designed to ensure that oysters are only grown in areas with appropriate water quality. Oyster farmers have to be particularly aware of the signs of QX oyster disease, which is caused by the microscopic parasite Marteilia sydneyi. The spore-like parasites invade an oyster's digestive system and multiply in the digestive gland or 'liver'. These spores are so numerous that the oyster is unable to absorb food and can starve to death within 40 days of infection. Oyster fatality in an infected bank can be as high as 95 per cent. Although QX is usually fatal to oysters, there is absolutely no evidence that it is harmful to consumers.

A sign of QX infection is a mass mortality of oysters, though a thorough and correct diagnosis can only be obtained by microscopic examination of the digestive gland for the detection of QX spores. Samples of oysters suspected of QX can be sent away for examination. Once infected, oysters cannot be cured of the disease, but it is still possible to farm oysters in QX-susceptible areas within certain operating constraints. The risk of infection is year round but highest in the summer months.