The cultivation of oysters and scallops by the suspension method The cultivation of oysters and other bivalves of the Ostreidae family is becoming an increasingly popular and profitable activity among aquaculturists in various parts of the world. Today, countries like Japan, France, Chile, the United States, Spain, Peru, Mexico and Australia are large aquaculture producers that receive large economic benefits from this activity.
Oyster reproduction Bivalves are a hermaphrodite species and change sex in the course of their life, functioning first as males and then as females within the reproductive cycle. Their life cycle includes two phases of larvae, which are microscopic and are categorised as zooplankton. During the larval stages, mortality is high due to competition with other species for space to attach themselves, predation, variations in temperature and salinity, among others. In the second stage, the larvae fix themselves to a surface by means of a peduncle, thereby initiating their sedentary life and developing their shell. When the shells are visible to the naked eye they are said to be in the seed stage, during which their feeding level increases. Oysters reach sexual maturity after one year, and take between 10 and 13 months to reach a considerable size (7-12 cms is the commercial size).
Requirements for oysters Oysters like other molluscs are fed by filtration and it is estimated that they have the capacity to filter about 150 litres of water per day. By this method, they obtain small organic particles (eggs, protozoa, algae) that are suspended in the liquid. The water where they grow needs to have a certain degree of salinity, and contrary to what many people may think, water that is cloudy due to suspended organic particles, is more nutritious for the oyster. The optimal pH of the water is equal to that of the sea under normal conditions (7.5 to 8.5).
How is an cultivation of oysters carried out? It is for the above reasons that cultivation of oysters is carried out within special meshes, able to withstand the salinity of the water, the solar radiation, the temperature changes and the roughness of the shells of the oysters. They also provide protection against seabirds. The temperature of the water is immaterial, because these species can develop in cold or warm climates. However, in the case of cold climates, it is recommended that the crops be submerged a little, so that the surface layers of ice do not harm the oysters. The most suitable terrains are natural marshes with low swell and low water levels, so that the farmer can have easy access to the nets he places. Alternatively, crevices can be created in the terrain to create small ponds that work as plots.
Surface cultivation Cultivation of oysters on the surface of the water is becoming an increasingly popular practice around the world. To achieve this, farmers are using floating systems of one, two, four and six bags into which oysters are introduced at seed stage. On the surface, food (phytoplankton and zooplankton) are abundant. The movement of the waves helps to shape the deep oyster cup and growing bags provide shelter from predators. Mesh bags allow adequate water flow, giving oysters all the nutrients they need to grow. The bags should be approximately 110 cm x 60 cm, with a mesh size of 5 mm to 1.5 cm. Once the bags are filled with seeds, they are placed in rows, fastened with floats and tied together to make best use of the space. They are anchored by stakes so that they keep the nets on both sides in a row, and are kept under observation until the oysters have grown to at least the minimum commercial size (7cms). Where can I get the necessary equipment to grow this type of crop? HORTOMALLAS, is a company that is characterized by the quality of its products, specializes in all kinds of meshes as well as supplying many other agricultural equipment.