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The aquaculture for oysters, mussels, pearl oysters, and
sea squirt are based on the long line system. In the system, the longlines are
horizontally stretched on the surface of the farming ground with the aid of
floats fixed to the location. To the longline on the water surface, vertical
ropes holding cultured species are attached downward with a regular interval.
The locations of the system should be contamination free, algal foods rich,
and deeper than 5 meters in common.
1. Longline system for Pacific oyster The longline based oyster aquaculture in Korea is
practiced on the southeast and middle of the southern coasts, including Tongyoung
blue belts where the water depth are 5∼20m. The longlines are 100m long
and stretched in a parallel way with the interval of 5∼10m in width. The
floats anchored firmly to the bottom keep the longlines on the surface of the
water. The vertical ropes are hung from the longline with intervals of 50∼70cm
to which seed collectors are attached with intervals of 30∼ 50cm. Normally,
the lines are of polyethylene and the floats are of styrofoam .
Longline culture system
for oysters.
1-1. Seed production of oyster
The seeds for oyster culture in Korea are wild or hatchery-based.
The seed spats are captured on collectors which are suspended from lines within
1 meter in depth. The seed collector is a string of scallop shells threaded
on a wire of about 1 meter length. A seed collector has about 50 scallop seeds
threaded together on a polyethylene wire. To capture absolute oyster seeds on
the collectors, the collectors should be set on time when oyster larvae predominate
the seedling grounds. A care should be given not to have barnacles attached
on the seed collectors. Failures are frequently resulted from the attachment
of barnacles which are a competitor to the collectors. Therefore, oyster aquaculturists
are busy monitoring the oyster larvae during the spawning season from June to
September.
It is now possible to obtain seed oysters attached on the
collectors in the hatchery, so-called hatchery-based seeds, which eliminate
the laborious works on the sea and worry about the failure of seed collector.
Two of the prominent advantages of hatchery-based seed production are to have
seeds from healthy broodstocks in physiological and genetic senses and to have
seeds the farmers need in time. These are because the hatchery researchers can
manipulate reproduction-related environmental factors to have the healthy broodstocks
spawned in their hatcheries. Temperature manipulation is one of the routine
factors to control the reproduction of the oyster. In the hatchery, algal foods
such as Isochrysis galbana, Pavlova luteheri, Chaetoceros calcitrans, Tetraselmis
suecica, Phaeodactylum tricornutum, etc. are served singly or in a combination
manner for the nutritional balance.
1-2. Hardening of the seed
The oyster seeds collected in June to July (early seeds)
grow fast to 10mm in shell length by the end of September when the spat numbers
are 25∼30 per collector. The oyster seeds can go to on-growing culture after
2 to 3 weeks after attachment or can be hardened by September before on-growing.
The oysters spats grow to market size by the coming winter or spring. The oyster
seeds collected in August to September (late seeds) are hardened until coming
spring when they move to on-growing system. The hardening is achieved by fixing
the seeds attached on the collectors in the middle of intertidal zone to have
the seeds exposed to air and surfs in a regular manner. The hardened seeds are
smaller but stronger compared with those submerged all the way. Once moved to
on growing system, the hardened oysters are growing faster and more resistant
against diseases over those unhardened ones.
1-3. On-growing
Hardened or unhardened oyster seeds move to on-growing
system. In the system, 10∼25 collectors are attached to vertical rope of 2∼6m
length. The culture continues until harvest.
2. Longline system for pearl oyster
The longline system for pearl oysters are set in the coastal
waters where water temperature and depth are suitable. The pearl oysters are
cultured on the southeast coasts of Korean peninsula where water depth are 5∼10m.
The basic culture system for pearl oysters are same as that for Pacific oysters.
None of hatchery-based seeds are available.
Longline
culture system for pearl oysters in Korea.
3. Longline culture system for sea squirt
The operation of the longline system for sea squirt are
in the coastal waters of the southeast and southern parts of Korean peninsula
where water depth are over 10m. The culture system for the sea quirt are also
same as that for Pacific oysters. The sea squirt seeds are available from the
hatchery in Korea.
Longline culture system for sea squirt
1. Float-system for Porphyra
Ecologically Porphyra need to be exposed to the air from time to time. On ground that is unsuitable for rack building (fixed pole system), floating rafts are used. Floating frames made of plastic tubing are used for this purpose. Up to 100m of nets can be attached to a single frame. Having been brought to the site, the frame is slotted into the raft in such a way that the nets are exposed to the air for 3-4 hour every day. Styrofoam floats are placed under the framework when it is necessary to lift Porphyra out of the water. Nylon frames, anchored to the seabed at the corners, are also used and supported by floats
2. Longline system for Undaria and Laminaria
"Longline system", in which cultivation ropes are stretched in parallel with the main. The cultivated ropes are checked every month to thin the plant densities and to remove trapped debris and fouling organisms. The plants are kept approximately 1~2m below the surface.
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KOREA-US AQUACULTURE -> Korean aquaculture ->Technology->Hanging
culture
