♦ Scientific name: Haliotis discus hannai

♦ Common name: Ezo abalone

♦ Distribution

About a hundred abalone species are found through the world. Of them, 6 species are distributed along the coasts of Korean peninsula. They are H. diversicolor supertexta, H. diversicolor diversicolor, H. discus hannai, H. discus, H. sieboldii, and H. gigantea.

♦ Ecology & habitat

The species of abalones are separated by two groups on the basis of winter temperature at water depth 20 meters, so called warm water species and cold water species. Haliotis gigantea, the biggest species found in Korean waters, grows up to 250㎜ in shell length and habitats Jeju Island in the water depth of 50 meters. The spawning seasons of the species are November to December. Haliotis discus hannai, one of the most common species cultured in Korea, is cold species inhabiting the main land. The species, sized 120~180mm in shell length, spawn in June to July.

♦ Aquaculture

Abalone (genus Haliotis) are a marine mollusc and similar to garden snails in that they possess only one-shell (unibalves) and they have a large muscular "foot" which they use to attach themselves to reefs and similar substrates by suction. It is this foot which is the edible part of the animal and is considered a great delicacy by a number of Asian cultures. High prices are paid for abalone meat, which constitutes between 28 to 46% of the abalone's live weight (depending on season and location). Six species of abalone have been reported to occur along the Korean coasts, Haliotis discus hannai Ino, H. discus discus Reeve, H.madaka Habe, H. gigantea Gmelin, H.diversicolor supertexta Reeve, and H. diversicolor diversicolor Reeve.

• Life history

The fertilized eggs are dispersed by currents until they hatch into motile larvae known as veligers. The veligers undergo a number of other development stages for 4 to 6 days until they settle. Once settled the juvenile abalone are called "spat" and they graze on the microalgae which is present on the substrate. Spat can actively select a suitable substrate depending on the level of food availability. Once the spat have reached approximately 5mm in size, they make their way into rock crevices for protection and come out at night to feed on drift seaweed.

• Aquaculture technique

Abalone farming was first developed in China and Japan where it was used for re-seeding the wild-fishery. From here it spread to various countries. In fact, abalone farms in various countries are still developing their own techniques to suit their production systems and market requirements.

• Techniques and equipment

Though the basic techniques for rearing abalone are similar the world over, specific details vary widely, often changing from one farm to the next. This diversity is a reflection of both the variety of conditions in which abalone are raised and the relative infancy of the industry. Many farms are still experimenting with methods and equipment, trying to find the perfect set-up to maximise production and minimise costs. The following outline is a summary of the most commonly used techniques and equipment used in Korea.

• Broodstock

The first step in culturing abalone is obtaining broodstock (sexually mature adult abalone). Broodstock may be gathered from the wild by those who hold a permit to collect wild abalone or through a licensed quota holder. The other alternative is to obtain broodstock from previously cultured stock. Since wild stocks are available in Korean waters, a number of farms make a point of mixing wild and cultured abalone so as to maintain the hardiness of the stock. Wild abalone only reproduce during a specific period and wild-caught broodstock are collected during this period. The condition of the gonad indicates the abalone's readiness to reproduce. Those animals with very swollen gonads are collected, and male and female abalone are placed in separate tanks. The sex of an abalone is determined by the colour of its gonad; sexually mature males have a creamy yellow gonad whilst sexually mature females have a dark-green gonad.

• Spawning and settlement tanks

The abalone broodstock are induced to spawn by warming the water in each tank, simulating higher ambient spring and summer water temperatures, and treating it with ultraviolet light. An hour or two after increasing the water temperature, the abalone release their gametes into the water. They are then collected and mixed together in larval rearing tanks. With experience, farmers can learn to add just enough of each to produce a million fertilised eggs. Once fertilised, the eggs sink to the bottom of the tank. Depending on ambient water temperature, it takes 18 to 24 hours for the eggs to hatch into free swimming larvae called veligers. The veligers stay in this stage for the next 4 to 6 days feeding off the naturally occurring plankton in the water. The water needs to be changed regularly and the temperature needs to be maintained between 15°C and 18°C . Once the majority of eggs are hatched into veligers they are moved into settlement tanks. These tanks contain a series of settlement plates and use a downward flow of water which induce veligers to attach to the plates and metamorphose into juvenile abalone (spat). Settlement plates are pre-conditioned for spat settlement, ie they are coated with microalgae called benthic diatoms. The spat graze on these plates just as they would on rocks and reefs in the wild. The spat spend from 8 to 12 months in the settlement tanks, until they grow to a length between 10 to 15mm. At the end of this time transferred to grow-out tanks. Abalone are very sensitive to stress; excessive handling during the production process causes high mortality rates and reduced growth rates. Thus, all stages of production must involve minimal handling and disturbance.

• Grow-out

This is the phase where the diversity between farms becomes most apparent. Not only are there a number of established techniques used in grow-out (see below), but a variety of new ones are being trialled in order to determine which are the most effective and economical under varying conditions.

• Broodstock

Abalone grow best on a diet of red algae and similar seaweeds. However, the large volumes of seaweed required to commercially produce abalone inhibits the use of natural occurring feeds. Consequently the majority of farms use artificial feeds with a proper balance of amino acids, minerals, vitamins and calcium to replace seaweeds. It should also hold together in the water for several days and be palatable to the abalone. The feed has to have a good texture that the abalone will find attractive.

• Grow-out facilities

    - Land-based raceways and circular tanks These tanks are generally shallow and made of industrial-strength black plastic. They are often covered with green-house mesh to stop predation and provide shelter for the abalone. Seawater is pumped from the sea and through a sand filter before being pumped continuously through the tanks. The abalone enjoy the fast-flowing water provided by flow-through systems.

    - Barrel and cage culture Both techniques are similar in principle in that they are divided into a number of sections in which the abalone are placed inside and allowed to attach. The barrels and cages are placed in the open sea and secured to the sea-floor by longlines and anchors or attached to rafts. The barrels and cages are open, ie covered with mesh, allowing water to circulate while serving to keep the abalone inside and protected from potential predators. The main source of food for the abalone is kelp and similar seaweeds placed inside the holding facilities. They are checked regularly to ensure that the abalone are intact.

• Harvesting

Most abalone are harvested at the end of their third year when they have attained a size of approximately 70mm (or 50g in-shell wet weight). The market for abalone seems to start with animals as small as 50mm and to extend through to animals 200mm long. The smaller size of cultured abalone has proved to be very popular in the South East Asia market. Asian cuisine prefers to serve whole portions rather than to divide up a portion between serves. The large size of wild caught abalone makes such an approach both impractical and expensive. These smaller abalone have come to be referred to as cocktail abalone to distinguish them from the larger wild-grown animals. Depending on the market, abalone are either transported live to the buyer or they are shucked (de-shelled), cleaned and processed. The meat is graded and is then either frozen, cooked in brine and canned, or dried and vacuum packed. Hong Kong and Japan are the main importers of abalone in the world. In terms of value and quantity, canned abalone is the largest imported item with frozen, live and dried abalone following.

Female spawner	Male spawner	Spawning	Rinsing eggs shedded
Hatching chamber	Fertilized eggs	4-cell stage	32-cell stage
Hatched larva	Ready-to-attach larva	Seed collectors	Spat culture
1㎝ long spats	2㎝ long spats	Spat shipping	Releasing

                  Procedures for the seed production of Haliotis discus hanai.
 

Abalone seeds attached on the substrates. The seeds are ready to be released into the farming ground or to go the land-based farms.	Divers are harvesting abalones in their farming grounds where juveniles were released 3-4 years before.
Farmers are feeding abalones in the submerged cages with rooted seaweeds. The culture system is recently introduced into the abalone farming.