#Size of oyster spat full#

The Pacific oyster is the species most commonly used with this type of farming. This cultivation technique is the least susceptible to predators and poaching, but is the most expensive and labour intense to build, manage and operate. The carbonate minerals calcite and aragonite in the water help oysters develop their shells faster. In particular the temperature and salinity of the water are altered somewhat from nearby sea water. The maturation tank is fed with water that has been especially prepared for the purpose of accelerating the growth rate of the oysters. In the third method the spat or seed are placed in a cultch within an artificial maturation tank. The latter method avoids losses to some predators, but it is more expensive. Oysters cultivated this way are harvested by lifting the bags or racks to the surface and removing mature oysters, or simply retrieving the larger oysters when the enclosure is exposed at low tide. In the second method the spat or seed may be put in racks, bags, baskets or cages (or they may be glued in threes to vertical ropes) which are held above the bottom.

Such oysters will then be collected or harvested using the same fishing methods that are used for wild oyster harvesting, most commonly dredging. In one method the spat or seed oysters are distributed over existing oyster beds and left to mature naturally. The maturation technique is where the cultivation method choice is made and where the oyster’s unique taste, quality and appearance is formed. In either case (spat or seed stage), they are set out to mature after approximately six months. The loose spat may be allowed to mature further to form ‘seed’ oysters with small shells. After the larvae settle, they are considered ‘spat’.

#Size of oyster spat full#

The best cultch is usually full or ground up oyster shells because oysters are naturally attracted to other oyster shell to ensure their future reproductive success. When this happens, the oyster larvae are ready to move into nurseries which are usually outdoor systems in ambient water with a variety of cultch options. In two to three weeks, the larvae develop an eye-spot and a foot, a sign that they are ready to latch on to a hard substance. This is the most fragile stage of an oyster's life history. Here it is important that the water is clean and changed regularly to ensure no pathogens or foreign organisms enter the system and compete with or eat the larvae. There can be as many as 110 million fertilised eggs in 7,000 litre tanks in the rearing rooms depending on each farm’s capacity.Īs soon as the eggs are fertilised, the beginning-stage larvae are fed with cultures of phytoplankton (algae) on a daily basis. In the hatchery, fertilisation of eggs with sperm takes place within minutes and cell division occurs over the next 24 hours. It is important to have a large number of oysters, because it is impossible to tell if an oyster is male or female from its outer appearance. These oysters are the “parents” or base of an oyster farm that provide the gametes. water composition, temperature, food and light are all controlled and nothing is left to chance.įirst of all a solid and high qualitative broodstock is key to successful oyster farming. The first few steps are carried out in a controlled tank environment, i.e. Generally there are about five steps involved in oyster farming. The two main oyster species that are farmed are Ostrea edulis (the European flat or native oyster) and Magallana gigas, the introduced Pacific oyster. Donegal and Waterford accounting for about 60% of the Irish production. This includes Irish rock oyster farms as well as farms for the native flat oyster.Īs mentioned on our history page, in Ireland there are currently around 130 oyster farms nationwide having producing 10,300 tonnes of oysters worth over €44 million in 2019 with Co.

Figure 1: Regional Distribution of farmed oyster output from the BIM aquaculture report 2019.