The necessity of management for wild resources in the sea has been risen from 1970's. In 1980's, the reduction of fishery strength and preservation of wild broodstock and fry was operated by government through innovation of the Act for catching activity. Artificial fish bank and fry stocking activities have been enforced into the sea for enhancement of natural resources.

The releasing program for enhancement of natural populations was started in the early of 1960's by releasing salmon fry into the sea off the eastern coast of Korea. In the middle of 1970's, including abalone, littoral zone habitat organisms were released in the all around Korean peninsula. Marine ranching and stocking enlargement are become a major policy of the government of from 1980's. The major target organisms were fleshy prawn, black rockfish, olive flounder and black sea bream. Since then, total of 42 species have been used for enhancement of stocking, among that 19 species of fish, 11 species of shellfish, 4 species of crustaceans and other 8 species are including (see table as below).

Total 42 Species:

Finfish 19 Olive flounder, Red seabream, Black seabream, Parrot fish Black Rock fish, Rock trout, Grey mullet, Sea bass, Sweet fish Puffer fish, Sand flounder, Starry flounder, River puffer Scorpion fish, Red scorpion fish, Rabbit fish, Sting fish Spotted sea bass, etc.

Shellfish 11 Abalone, Top shell, Ear shell, Scallop, Hen clam, Surf clam Purplish Washington clam, Clam, Pearl oyster, etc.

Crustacea 4 Tiger prawn, Fleshy prawn, Blue crab, River crab

Others 8 Purple sea urchin, Sea cucumber, Sea squirt, etc.

 

Stock assessment

- general

The researches for the effect of releasing of artificially-reared offspring on improving stock enhancement have just started from the middle of 90’s. Main target organisms of the release were black rockfish, olive flounder, and Kuruma prawn.

For the black rockfish which is commonly distributed in coastal area had investigated the effect of releasing by the mark of fin-clipping and ALC from 1995 to 1999 at Kyuck-Po site in West Sea. The amount of the catch of this species at release site was twice larger than before the release.

In case of olive flounder the maximum catch rate were increased 83.5% in landing survey from 1995 to 1999 in South Sea.

And Kuruma prawn also the effect of releasing resulted the catch at the release site increased 3.6 times than before the release.

However the release effect of artificially-reared offspring was different to species and region due to the fluctuation of environment, feeding organisms, predator, and etc.

From the middle of 70’s totally more than 0.3 billion offspring have been released to natural environment for stock enhancement in Korea. It was very lucky to start Responsible Stock Enhancement Program of Korea that the released offspring was small and sixty million in 2000.

First before the conducting large scale of a release for stock enhancement we must assess scientifically wild stocks in ecological, behavioral, physiological and genetic processes. Best stock enhancement is the increasing of wild numbers or populations with control catch. However the demand of fish as a food has creased more and more, the Stock Enhancement Program just start in a large scale. Our goals of this program are to preserve wild stocks and to minimize the risks of releasing.
 

- Genetic assessment by microsatellite DNA

The broodstock for the production of artificial offspring have a small gene pool, so the stocked offspring which could be made from a single mating couple can lead to an increase in the fluctuation of gene frequencies and decrease genetic polymorphims in the wild.

Many artificially reared offspring have been released into the natural environment without considering the influence on genetic variability although the understanding of genetic structure and genetic diversity is one of the most important steps for useful management of fishery resources. Therefore the stocking of artificially reared offspring should be carefully done with a better understanding and appreciation of genetic variation and divergence in order to preserve natural resources.
Our genetic researches for black sea bream, rock fish, flounder, white shrimp, etc. have been mainly conducted in stock enhancement using mtDNA and microsatellite DNA. 

Various kinds of DNA markers have been recently developed as genetic markers with the help of fish genetics and breeding technology. For the past 30 or more years, genetic population structure of various fish species has been studied by isozyme analysis.

Although, isozyme polymorphism has been useful as a marker for the identification of fish species and separating geographically isolated populations, it is not sufficiently sensitive for genetic analysis of geographically proximate subpopulations or populations. DNA fingerprinting has been proposed as a tool for reconstructing the pedigree of communally reared aquaculture populations.

Minisatellites and microsatellites are two classes of single locus DNA fingerprinting markers that are generally inherited in a Mendelian way and are thus potentially useful for pedigree reconstruction. Microsatellite regions consist of tandem arrays of core sequence repeats (from one to four base pairs) which often vary in length among individuals and sometimes have large numbers of length variants (alleles) segregating at a locus. It has proved to be a powerful tool for the assessment of genetic diversity of many fishes and the typically high number of allele at such loci may make them particularly sensitive to detecting inbreeding in aquaculture populations.

The Food and Agriculture Organization of the United Nations (FAO) experts (1993) recommended the conservation natural resources in their morphology, habitats, biology and in their gene (allele) composition of genome. Many researchers initiated to assess the affects that released fish have upon the genetic, health certification for diseases of wild population. Therefore the stocking of artificially reared seed should be carefully done with a better understanding and appreciation of genetic variation and divergence in order to preserve natural resources.

Genetic assessment in released black sea bream, Acanthopagrus schlegeli, has conducted a collaborated work between our institute and Aquaculture Lab. of Hiroshima Univ., Japan using microsatellite DNA, whether the release project would be effective in fishery management.

At the mass production of black sea bream offspring for release project, the heterozygosity was not different between breeders and offspring. And heterozygosity as a genetic indicator to assess genetic variability was shown genetic similarity with the wild population, indicating that there was no influence on genetic differentiation of wild population. However, the mean number of alleles per locus decreased less than 16.5%. Therefore, black sea bream produced from the limited numbers of parents were released into the natural environment might induce depletion of genetic diversity in wild population.

In pedigree tracing analysis, the actual contribution rate was 69.0% for females and 90.9% for males over two years. More than 30% of females did not participate throughout two years. Therefore, the number of broodstock, egg collection frequency during spawning season and induction of new broodstock should be considered to conserve genetic variability of wild population.

In the studies, MS marker showed the potential tool for genetic evaluation of black sea bream offspring. Therefore, all of the stocked offspring for stock enhancement program should be done with the appreciation of genetic divergence. And further researches are needed to find out the genetic influence on wild population.