♦ Scientific name: Sebastes schlegeli ♦ Common name: Black rockfish ♦ Ecology

  
 Black rockfish inhabits shallow rocky shores from 10 to 100 meters in depth along the all coasts of the Korean peninsula, Japan, and some parts of China. In Korea, the mature species produce directly their larvae in May to June. The species grow to 25cm in body length by year 2 and 30cm by year 3, feeding small fish, crustaceans, etc.

♦ Aquaculture

   The black rockfish, Sebastes schlegeli  has been studied since 1986 by NFRDI for aquaculture purpose. Currently, its artificial seedling cultivation method has been established. In reality, the rockfish together with olive flounder, occupies leading species farmed in marine environment.

   S. schlegeli seed production is done on hatchery in cylindrical or rectangular indoor tank.  By using mature fish about 3 years old, birthing is done during April and May.  Adult fish about 30¡­40cm big gives birth to about 100 to 200 thousands larvae. Early larvae is relatively big at the size of 5.7mm and starts feeding from the moment of birth.  For first 10 days they are fed rotifer at the density of 10/§¢ as introductory prey organism.  From 11th days to about 30th days, Artemia is fed at the density of 1¡­3/§¢ and mixed feed is supplied from the third day on and the size and quantity of the feed should increase gradually.  The introductory feed organism, rotifer and Artemia should be enriched with Chlorella.  When supplying mixed feed, green water and floor cleaning should be done every 3 to 5 days to stabilize the water quality.  Population density of 5000 to 7,500 larvae per §© is appropriate.  When fry reach the size of 2§¯, population density of 2,300 per §© is appropriate and when fry reach 3§¯ the density should be adjusted to 2000.  If the individual size of fry differ greatly, they might feed on each other, thus selection and separation is necessary.  To prevent disease, medicate after every 2 to 3 weeks period and when they reach the size of about 5§¯ they can be sold.
 

♦ Early seed production

   First distinctive feature of current  farming technique is early seed production.  With increase of nurseries in Taean and Boryung in west coast, lagging production, more efficient use of farming facility and the change of production type in existing flatfish farmers made the competitive power to be vital.  Therefore, nurseries try to produce high quality seedlings earlier than other companies.  Securing adult fish is important for such early seed production. There are two methods of securing mature fish.  The first is buying 3 to 4 years old S. schlegeli (25§¯ to 35§¯, weighs 1.5 to 3§¸) from Geomundo or Koje of south coast right before the birthing at high price and the second is to buying the breeding fish around January and raising them in increased water temperature of 13 to 14¡É and reduce the time of birth to 20 to 30 days.  However, increased water temperature farming requires about 60 days of gradually increasing water temperature and fully equipped water temperature facility thus serious consideration of fuel cost and economical efficiency is necessary.  With such efforts, seed production, which would normally be produced in mid April, has been reduced to early April by 1 to 2 weeks.

Cage culture of  Sebastes schlegeli.  Majority of black rockfish are cultured in the net cage system.   

♦ Seed production in open field

   Recently, artificial sea cultivation has been active and large scale plantation are being built around Chungnam Taean; west coast. However, natural cultivation from abandoned open field is becoming an alternative method.  Originally, open sea fond had been used as Penaeus orientalis farm but due to viral infection it had been abandoned and used as settling tank to stabilize water quality.  However, due to high coast and lowering quality of seed production in dry land plantation, open field cultivation became a solution for lower production cost and higher quality.  Seed production method in open field; fertilize water and mass-breed the prey organism and then barricade one side to contain large number of breeding fish.  After the birthing let the seedlings grow in natural environment. This method has lower production cost than the dry land cultivation and the feeding is dependent on natural prey which also controls the population density. However, cost of acquiring breeding fish is relatively high and difficulty of managing such large field under human control is the downside of such method.  Therefore, under current circumstance of not having proven cultivation method, although there are differences among different farms, open field cultivated seedlings are preferred due to their stronger immune system and faster growth rate.  Competition in the seed production market will depend more on the quality of the seedlings rather than the quantity in the future and the open field cultivation will probably become more and more popular.
 
♦ Cultivation

   A cultivation of S. schlegeli means to purchase seedlings and to raise them to 500g¡­1kg in weight to be sold in market which takes about 18 to 24 months.  The fish are cultured in embankment and cages.  The cage cultures are more common.  Quality good seeds show a strong schooling behavior. The cage cultured for the species are of 5m X 5m or 10m X 10m with 22¡­27 nodes net cage for seedling s the size of 4 cm to 5 cm.  When they reach weight of 30¡­75g use 18 net, 10 nodes for 75g¡­135g, 7 net when they grow over 135g.  For cage method, appropriate population density is 700¡­1000 per §© at the size of 4cm to 5cm and 300 ¡­ 500 at past 8 cm.  However S. schlegeli do not like high temperature.  Therefore, water should be exchanged often and population density should be reduced to half the normal level during summer.  They should be fed 2¡­3 times per day when they are young. It should be reduced depending on their growth and by the time they can be sold, they should be fed about 1¡­2 times a day. During the winter with low water temperature, every 2 to 3 days feeding scheme is advised.  For S. schlegeli cultivation, recording of seedling provider and the condition should be done.  In case of sick fish or abnormality fast and appropriate response is necessary.
 
♦ Disease

  There are many efforts to prevent  and cure diseases during cultivation and summer period needs more attention during high water temperature.  To prevent disease, it is recommended to temporarily stop feeding and provide fresh feed.  Preventing contagious viral infection by maintaining appropriate population density and fast responses, such as providing oxygen and medication during red tides or outbreaks, are necessary.  Especially, careless overdose of additives that are sold recently can have serious impact on the immune system so they must be used with care.  Such precaution and diagnosis can prevent abnormality and mass suffocation which will result in improved product quality and maximized profit.
 
♦ Prospect of cultivation technology and development for the future.

   Difficulties of cultivating S. schlegeli comes from problem of introductory prey organism, high cost of production, low profit from over-production, and lowered quality of seedlings from mutation.  The development of introductory mixed feed is necessary to solve these kinds of problems and research to find introductory micro feed to substitute natural prey is in progress.  Lower profit from over-production should be handled by the companies themselves by changing production output and type.  Lowering quality of seedlings should be handled by researching into immunology and engineering with having competitive edge by securing high quality seedlings in mind.
  On cultivation, 70% of current sea barricades are breeding S. schlegeli which might cause lowered price from over-production. Therefore shipment timing agreements among companies and advertising to buyers seem necessary for the future.  
  As for the development goal for the future of S. schlegeli environment friendly cultivation method is necessary.  For this, development of high efficiency - low pollution feed is necessary.  For production of high quality seedlings, change in open field cultivation method is needed.  Also, with mutual trusts of each farmers, adjustment of market sold timing, output, and production type is necessary.

Culture tank for seed production of Sebastes schlegeli	Juveniles of Sebastes schlegeli
Selecting of juveniles