1. Scientific name: Anadara broughtnonii

2. Common name: Ark shell

3. Distribution

   Anadara broughtnonii is one of the most economic species belonging to Anadarinae which distribute in Pacific coasts including Korean coastal waters. The species has common appearance characteristics with A. satowi, but they differ in shell thickness and vertical distribution. A. broughtonii distribution goes down to 50 meters in depth, while A. satowi  is limited within 30 meters in depth.

4. Aquaculture

   The spawning seasons of the arkshells are normally July to October with major spawning season of July to August on the southern coasts of Korea. For A. broughtonii, the spawning occurs mostly from August to September. The size of the spawned eggs is about 55 ??in diameter. The species grows fast; the eggs spawned in September reach 31.6??65.9 mm by year 1 and 48.7? ?8.1 mm in shell length.

   For the seed production, the wild brood stocks weighing 100 to 200g (7??0cm in shell length) are purchased and kept in captivity with supplement of algal foods for maturation. During the maturation conditioning, a special care should be given not to have the brood stocks spawned in the conditioning tanks. Water temperature over 23??can stimulate the spawners to spawn.

   Besides water temperature, exposure to air, chemicals, electric shock, and presence of sperm can be stimulators to spawning of the shell. For water temperature stimulation, sudden increase of water temperature to 5??has been routinely used in the ark shell hatchery. The fertilized eggs are to be washed with the aid of egg washing net (mesh size, 20??. Larvae of ark shell are growing under water temperature of 24  26??and illumination of lower than 100Lux. For the best growth, the D-shaped larvae should be contained in densities 5??0/mL. Water exchange is performed on every two-day basis.

   The ark shell larvae metamorphose to attaching larvae when they reach 260??in shell length. Normally, it takes about 20 days at 25??until the metamorphosis. Just before the metamorphosis, substrates for larval attachment are to be inserted in the larval culture tanks. The attached larvae move to nursery ground before they go to the farming ground.   

   The ark shell larvae are to be fed continuously with a mixture of Isochrysis galbana, Chaetoceros calcitrans, and Monochrysis lutheri. The algal densities supplied depend on the sizes of the larvae, normally 0.5??x104cells/ml

  
The procedure for the seed production ark shell practiced in the Namhae Marine Hatchery of NFRDI

5. Recent problem in the ark shell aquaculture.

Ark shells are one of the farmed species facing difficulties in the production. The prolonged practice of the aquaculture brings local failures of wild seed production. The production decrease is particularly evident since 2000. There might be several reasons for the local failure of the seed production. One of the most significant reasons is local appearance of unhealthy brood stocks in the seeding grounds. Unit production is also shows a decreasing trend, worsening farming ecology in locations. NFRDI shellfish research team are continuously monitoring the health of the wild population. Fluctuation environmental factors are also monitored, including water temperature, salinity, dissolved oxygen, kinds of dissolved organic matters, food organisms, and chemical contaminants both of organic and inorganic matters in the seed and farming grounds. Hatchery-based seed production is also increasing. All these efforts have been practiced cooperatively with local fisheries institutes.   

Chart below shows Farmed production of ark shell 1970 through 2001.

 *K'nam: Kyungnam province (Data: MOMAF Fisheries Statistics))