To recover from the decline of a fishing grounds production capacity due to eutrophication in Mikawa Bay, it was examined by a benthic ecosystem model to find out the optimal arrangement of tidal flats, sea grass and seaweed beds, and beach which show maximum purification ability as a whole. In the summer, DIN became a sink (36-92mg N m^-2 d^-1) for most cases except for both cases of tidal flats occupying whole area (-87mg N m^-2 d^-1) and sndy, beach occupying whole area (-38mg N m^-2 d^-1). PON became a source (-3-100mg N m^-2 d^-1) for most cases except for the case of tidal flats occupying whole area (33mg N m^-2 d^-1). In these results, TN became a large sink in the case of higher occupation area ratio of sea grass beds, and it became a large source in the case of tidal flats occupying whole area and sandy beach occupying whole area. In the autumn, DIN became a large source (-73-199mg N m^-2 d^-1) except for the case of sandy beach occupying whole area (21mg N m^-2 d^-1). PON became a large sink (70-307mg N m^-2 d^-1) except for the case of sandy beach occupying whole area (-41mg N m^-2 d^-1). In these results, ability to remove for PON became larger with an abundance of macro benthic organisms.

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It is an urgent need to establish ecosystem-based approaches to the evaluation of coastal habitat values for habitat conservation/restoration and sustainable utilization of coastal fishery resources. In this paper, recent research activities related to the above-mentioned task are reviewed and re-organized in light of major functions of the coastal ecosystem. It is proposed that habitat values should be evaluated in two directions: ecosystem stability depending on the species diversity and smoothness of material circulation, the latter of which directly links with material removaVrecycle. In addition, reproductive capacity as a nursery for fishery resourcm should be included in the evaluation. For further development of the ecosystem-based approach, it is of great importance to accumulate long-term records of biological and ecological changes in the coastal water. In such context, newly emerged concept on the health examination of marine coastal environment is also discussed.

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Mapping of seagrass and seaweed beds is very important for management and conservation of sound littoral ecosystems and sustainable fisheries in the coastal waters. The methods to map spatial distribution of seagrass and seaweed beds are reviewed. They are classified into two categories. One is a direct method by visual observation and the other is an indirect method using a remote sensing apparatus. Indirect methods are divided into optical or hydro-acoustic methods. Indirect methods require sea truth by direct methods. Optical methods are image analysis of aerial photography or satellite imagery. They are effective for mapping broad areas but limited to shallow waters due to light attenuation in waters. Hydro-acoustic methods such as an echosounder and a side scan sonar have no limitation of turbidity. The echosounder is practical to map vertically density and height distributions of seagrass and seaweed beds. The side scan sonar is appropriate for mapping broad horizontal distributions. Coupling of several indirect mapping methods is more useful than using only one method.

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Recently it is stressed that sustainable development is indispensable for fisheries. It requires rational use of the sea, especially in the coastal area. Since there are a lot of aquaculture facilities in coastal waters, it is necessary to localize and count them for management of coastal fisheries. Thus we developed an easy method to map and count them using IKONOS satellite image with high resolution. Processing IKONOS imagery of Yamada Bay, one of rias-type bays in Sanriku Coast, aquaculture facilities for scallops and oysters were analyzed. Two types of aquaculture facilities, wood-raft type and buoy-and-rope type, were identified and examined. The method developed in this study can be applied to not only rias-type bays but also other coastal waters.

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In order to evaluate the carrying capacity of Otsuchi Bay, Iwate Prefecture, Japan, natural fluorescence method was examined for continuous monitoring of chlorophyll a and primary production. Light-absorption coefficient of phytoplankton (a_ph) and the quantum yield ratio of photosynthesis to fluorescence (Φ_c/Φ_f) needed for estimation of primary production from natural fluorescence were obtained from the water sample. Variation in aPh' was significantly correlated with chlorophyll a. Quantum yield ratio (Φ_c/Φ_f) showed significant correlation with photosynthetically available radiation (E_??__PAR) and chlorophyll a. Chlorophyll a and primary production estimated from natural fluorescence by moored sensors were in good agreement with those obtained by water sampling.

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Annual study was conducted in Tokyo Bay to investigate the influence of anthropogenic influx on phytoplankton community and concentrations of transparent exopolymer particles (TEP). Enhancement of TEP as a result of high phytoplankton biomass was observed with an empirical relationship between TEP and chlorophyll a. Of the phytoplankton groups derived by the CHEMTAX analysis using pigment composition, diatoms invariably dominated the phytoplankton community. Multivariate analysis between TEP and chlorophyll a of different algal groups indicated the major influence of diatoms and raphidophytes on TEP concentration. Laboratory experiments conducted with Skeletonema costatum and Heterosigma akashiwo confirmed the higher contribution of H. akashiwo to dissolved organic matter production and subsequent TEP concentrations. In addition to phytoplankton biomass and composition, growth stage of the organisms appears to be an important factor controlling TEP concentrations in the aquatic ecosystems.

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In May 2000, an experimental artificial tidal flat, based on dredged bottom mud and covered with sand, was constructed in Osaka Bay, Japan. We measured dissolved oxygen consumption by bottom sediments and some other environmental indicators such as sulfate reducing bacteria (SRB) to estimate the water-purifying potential of the tidal flat. Viable counts of SRB in bottom sediments of the tidal flat area reduced from 10⁶ cells/g wet mud (June) to 10² cells/g wet mud (September and December). In September, biological oxygen consumption rate (BOCR) early in the evening, just before a high tide (17:40) was more than 40 times higher than that early in the morning, just after a high tide (6:10), whereas no difference was observed in chemical oxygen consumption rates (COCR). The biological respiratory activity in tidal flat seemed to change hourly. In December, COCR was not detected, however BOOR early in the evening kept the same level of that in September.

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A study on nutrient regeneration processes and measurement of their fluxes at the sediment-water interface was carried out in two different stations of Shido Bay (the Seto Inland Sea, Japan). Seasonal variations in bottom-water, oxygen uptake and benthic fluxes were measured during 1999 to 2000. The sediment oxygen consumption (soc) ranged from 16.6 to 21.4 mmol m^-2 d^-1. Net fluxes ranged from 471 to 2264 μmol m^-2 d^-1 for ammonium (NH₄⁺) and 39 to 216 μmol m^-2 d^-1 for phosphate (PO₄^3-). A step-wise regression model indicated that bottom-water temperature and DO described 73% and 72% of the variability in measured rates of NH₄⁺ and PO₄^3-, respectively. Concerning the stoichiometry of oxygen (O), nitrogen (N) and phosphorus (P) emission from sediment, an annual average of O:N and O:NH₄⁺ flux ratios is 19.6 and 18.3, respectively, indicating that denitrification was occurring in Shido Bay. N:P ratio showed variable values (9.2 to 22.2), which the yearly average of N:P ratio (13.2) was approached for estimating benthic denitrification, suggested that about 93.4 μmol m^-2 d^-1 was loss to N₂ gas, which was 7% based on the N flux. An annual average of N and P fluxes showed that the sediments were supplied to the bottom-waters with equivalent to 33% and 22% of primary production N and P, respectively, requirement by phytoplankton of Shido Bay.

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Despite economic crisis in Thailand, environmental degradation trends have not reversed. Several governmental sectors monitoring the status of natural resources are attempting to utilize organisms such as green mussel, red algae, Artemia and bacteria for waste water (shrimp farm effluent, in particular) biological treatment. Educational sectors are carrying out the researches on utilization of mangrove forests and vetiver grasses for domestic waste treatment. Moreover, studies on potential and application technique of benthic polychaetes, common seaweed, and other organisms fat sustainable development of coastal shrimp culture are focused. On the whole, lack of integration of knowledge, cooperation among involving authorities and participation in environmental protection by the public were evident as major problems on effective application. Further progress on bioremediation technology in Thailand should deserve more response on the development of coastal culture and waste treatment technology. Social awareness and cooperation from the public should be simultaneously encouraged.

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Degradation of nonylphenol polyethoxylate (NPEO_poly) was examined on coastal sediments collected at Shimonoseki, Japan. The populations of the bacteria that degrade ethylene glycol unit of NPEO_poly ranged from 10⁰ to 10³ per g of the sea sediment. When the sediment of station 7 was inoculated into the sterilized seawater enriched with NPEO^poly as a sole organic carbon source, the total count of bacteria showed a two-phased increase and reached the level of 10⁹ cells/ml in the second growth phase. A clear degradation of NPEO_poly was observed in the second growth phase, and the accumulation of NPEO with shorter ethylene glycol units was observed. Of the each 20 strains isolated from the two different growth phase, none of the bacteria of the first phase degraded NPEO_poly, while 17 strains of the second phase did. Gas chromatography suggested that the bacteria hydrolyzed the ethylene glycol chains by the mechanism of hydroxyl shift.

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Enclosed coastal seas are subject to organic enrichment of the sediment on the sea bed. The benthic environment with the organically enriched sediment is apt to be suffered from the occurrence of anoxic (hypoxic) bottom water and development of reduced conditions of the sediment with high levels of hydrogen sulfide. We have developed a method to treat the sediment with artificially cultured colonies of a deposit-feeding polychaete, Capitella sp. 1. In this study, we conducted the experiments with outdoor pools to measure how efficiently the artificially established patches of Capitella were able to decompose the organic matter daily added to the sediment in the outdoor pools.

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Eutrophic coastal bottom environments are often under serious oxygen depletion in a stratified summer season, and the heterotrophic activities in the environment decreased significantly. For improving such anoxic conditions and stimulating self-purification ability, we supplied light into the bottom water through an optical fiber and stimulated the photosynthetic activities of phytoplankton. Results indicate that 15 uE m^-2 s^-1 of irradiation always resulted in net production of dissolved oxygen (DO). In winter, on the other hand, when DO was sufficient but low temperature was the limiting factor for the heterotorphic activities, addition of psychrophilic bacteria stimulated the microbial activities in the bottom environments. These results indicate that the combination using optical fiber and psychrophilic bacteria is promising strategies for the bioremediation of eutrophic bottom environments.

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Improvement of the hypophysation technique in Israeli aquaculture has been achieved by introducing LH-calibrated carp pituitary extract (CCPE) as a spawning-inducing agent. The hypothalamic approach introduced in the '90 s combines GnRH analog and a water-soluble dopamine antagonist in a single injection. Profiles of LH, estradiol and 17α, 20β dihydroxy-4-pregnen-3-one (17, 20-P) and the progress in oocyte maturation determined in treated carp revealed how the two approaches reach the same end result. The transduction pathways of GnRH signal leading to LH release in fish were found to encompass the activation of Gq protein, PLC, phosphoinositide turnover, formation of IP₃ and diacylglycerol, Ca²⁺ influx and mobilization, and activation of PKC and PKA. Recent studies indicate that GnRH signal is further transduced to the nucleus via PKC and PKA converging at MAPK (extracellular signal- regulated kinase=ERK) to stimulate the expression of the common α and the LHβ subunit genes, while that of the FSHβ is transduced via PKA in a manner independent of ERK.

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The decapeptide gonadotropin-releasing hormone (GnRH) has a critical role in the neural control of vertebrate reproduction. To facilitate the establishment of reproductive biology in teleost, we have identified and characterized GnRHs and their receptors in an experimental model species, the medaka Oryzias latipes. Three GnRHs and two GnRH receptors (GnRH-Rs) were cloned from the medaka. Three GnRHs, designated medaka-type GnRH (mdGnRH), chicken-II-type GnRH (cGnRH-II), and salmon-type GnRH (sGnRH), were expressed in separate brain loci (the preoptic area, midbrain tegmentum, and terminal nerve ganglia, respectively), supporting the idea that each form has a specific physiological role. On the other hand, the expressions of two GnRH-Rs, designated GnRH-R 1 and GnRH-R 2, overlapped at the tissue level; they were expressed both in the brain and in the pituitary. Despite such similar expression patterns, these two GnRH-Rs exhibited remarkably different ligand selectivities; GnRH-R 1 showed relatively high selectivity to all three native GnRHs in the medaka, whereas GnRH-R 2 had high selectivity only to cGnRH-II. Intriguingly, several lines of evidence obtained from structural, phylogenetical, and pharmacological studies suggested that a third subtype of GnRH-R remains to be found.

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Gonadotropins, FSH and LH, play a central role in mammalian reproductive process. In teleost, as in mammals, two distinct gonadotropins, GTH-I and GTH-II, have been isolated and characterized in many teleost species. However, with the exception of salmonids, the physiological significance of GTH-I and GTH-II in reproductive process is unclear at this time. This article focuses on physiological roles of GTH-I and GTH-II in male and female red seabream. The expression profiles of GTH subunit genes in red seabream during sexual maturation revealed that the levels of Iβ mRNA of male increased in association with gonadal development, whereas those of female were maintained at low levels. In contrast, IIβ mRNA levels of both sexes were maintained at high levels from the beginning of gametogenesis to spawning season. Furthermore, in vitro studies demonstrated that GTH-II is more potent than GTH-I in stimulating estradiol-17β production and cytochrome P 450 aromatase expression by vitellogenic follicles, while both GTH-I and GTH-II have similar potency in 11-ketotestosterone production in testicular slices. In addition, GTH-II, but not GTH-I, induced in vitro final oocyte maturation. These results suggest that GTH-II have important roles in reproduction of both male and female red seabream, while GTH-I shows sexual dimorphism in the expression of gonadotropin subunit genes and physiological function; GTH-I is functional molecule in male, but not in female red seabream.

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In teleost fish, as in mammals, two types of gonadotropins (GTHs) -follicle stimulating hormone (FSH) and luteinizing hormone (LH)-play important roles in regulating gametogenesis. To comprehensively understand the molecular mechanism of endocrine regulation of fish gametogenesis, we cloned two types of GTH receptor (GTHR) cDNAs from three species of teleosts: amago salmon, tilapia and sunrise sculpin. The receptors were classified into two structurally related groups, homologous with mammalian receptors for FSH and LH (FSHR and LHR). The two types of receptors from amago salmon were reconstituted in COS-7 cells and functionally identified as FSHR and LHR. We examined changes in their mRNA levels during the course of gametogenesis. In general, the genes for both receptors showed similar expression profiles in males, with a peak at spermiation. In females, the FSHR gene was highly expressed during vitellogenesis, whereas the LHR gene showed a reverse pattern and was elevated only during final maturation.

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To analyze gonadal sex differentiation mechanism in Japanese flounder (Paralichthys olivaceus), we examined the sexually dimorphic expression patterns of P 450 aromatase (P 450 arom), estrogen receptor-α (ER-α), ER-β and 11β-hydroxylase (P 450_11β) genes during gonadal sex differentiation period, using all phenotypic females or males that were generated by rearing genetic female larvae (all XX) at 18°C or 27°C during the sex differentiation, respectively. After the initiation of sex differentiation (day 60), P 450 arom mRNA level in the female gonads increased rapidly, whereas it decreased slowly in the male gonads. In contrast, after day 80, P 450_11β mRNA was detected strongly in the male gonads, but not in the female gonads. On the other hand, there were no differences in the levels of ER-α and ER-β mRNAs between the female and male gonads during the sex differentiation. These results indicate that estrogen plays a major role in ovarian differentiation, whereas diminution of estrogen biosynthesis may trigger testicular differentiation.

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The present study examined the ability of various steroids and hormones to induce in vitro spermatogonial proliferation in cultured testicular fragments of two teleost species. Results indicate that the three steroids 11-ketotestosterone (11-KT), 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-DHP) and 17β-estradiol (E₂) and salmon pituitary glycoprotein fraction (SPG) were able to induce DNA synthesis, spermatogonial renewal and/or spermatogonial proliferation in Japanese huchen (Hucho perryi), and 100 pg/mL of 17α, 20β-DHP was sufficient to induce spermatogonial proliferation in the Japanese eel (Anguilla japonica). From these results, we concluded that 11-KT is necessary for the initiation of spemtogenesis; estrogen is necessary for spermatogonial stem cell renewal; and 17α, 20β-DHP promoted DNA synthesis, and plays a significant role in the proliferation of spermatogonia during mitosis.

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We studied steroidogenesis in ovarian follicles during final oocyte maturation (FOM) and characterized the ovarian and testicular membrane receptors for progestogens in Japanese yellowtail. When intact follicles were incubated with radiolabeled precursors, a steroidogenic shift occurred during FOM, due to the inactivation of C 17, 20-lyase and the activation of 20β-hydroxysteroid dehydrogenase (20β-HSD), which resulted in progestogen synthesis. The progestogen 17, 20β-dihydroxy-4-pregnen-3-one (17, 20β-P) was the most effective inducer of germinal vesicle breakdown (GVBD) in vitro. Scatchard analysis of 17, 20β-P binding to ovarian membrane fractions revealed the presence of a single class of high affinity (Kd=22.9 nM) and limited capacity (Bmax=2.1 pmol/g tissue) binding sites. The specific binding of 17, 20β-P increased significantly during FOM and rapidly disappeared just after ovulation. In the testicular membrane fractions, specific binding of 17, 20β-P was also detected, with binding characteristics that were similar to those seen with the ovarian membrane fractions. The present results demonstrate that 17, 20β-P is a maturation-inducing hormone (MIH) in females, and suggest that the membrane receptor for 17, 20β-P is involved in the final gamete maturation of both male and female Japanese yellowtails.

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Basic information on reproductive endocrinology is lacking in tropical fishes, although tropical areas harbour a wide variety of fish species. This paper provides information on plasma sex steroid levels in tropical walking catfish maintained under stable warm water conditions for two years. It was ascertained that males and females maintained mature gonads capable of undergoing ovulation at any time during the experimental period. Fish never underwent spontaneous spawning, but a single HCG injection could induce ovulation at any time of the year. Such fish also ovulated and spawned in response to water level and temperature manipulation. Changes in water temperature probably increase the sensitivity of fish to the change in water level. Endocrine changes following HCG injection were also monitored.

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Vitellogenin (Vg) is the main precursor to egg yolk proteins (YPs) accumulated as nutrients for developing embryos of oviparous aquatic species. Recent gene cloning and immunobiochemical analyses verified the presence of multiple Vgs in teleost fishes, similar to the case in chickens and Xenopus. These findings lead us to abandon the classical “single Vg model” and explore different functions of individual Vgs and their YP derivatives during teleost oocyte maturation and embryogenesis. The course of proteolysis of Vgs and their YP products appears to differ among species. Detailed characterization of the relevant proteolytic enzymes has been partly accomplished only for salmonid fishes. Investigations of the endocrine regulation of teleost Vg and YP proteolysis have only just begun. Over the past decade, much attention has been paid to Vg due to its promise as a biomarker of contaminants that mimic estrogen, which are present in the aquatic environment. Sensitive and specific assays for measuring Vg in male and juvenile fish have been and will be valuable tools for identifying environmental estrogens to which humans and wildlife are potentially exposed.

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In Macrobrachium rosenbergii, distinct vitellins (Vn-A, B, C/D) exist in mature ovaries. A full-length Vg cDNA was obtained that encoded a mature protein of 2, 520 amino acid residues comprising the deduced sequences of these Vns. During ovarian maturation, cleavage occurs at two specific sites in the Vg molecule, producing smaller Vgs equivalent in sequence to VnA, B and C/D which are then incorporated into developing ovaries as vitellin. Using specific cDNA to examine the transcription of mRNA in candidate vitellogenin (Vg) synthetic tissues, the hepatopancreas was demonstrated to be the synthetic site of Vg in M. rosenbergii.

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The ELISA analysis with anti-scallop vitellin (Vn) serum demonstrated that an in vitro accumulation of Vn in the ovarian tissue was promoted with estradiol-17ß and cerebral plus pedal ganglion (CPG) extract which was heat stable. Estrogen-like immunoreactivity was found in the growing oocyte and auxiliary cell. It was supposed that the vitellogenesis occurred inside the ovary and an oocyte growth appeared to be controled by estrogen and CPG via estrogen receptor (ER). Vitellogenin (Vtg) cDNA clone was isolated from the ovary by immunoscreening and the putative protein exhibited 20% of homology, compared with Vtgs of other oviparous animals. RNA blot-hybridization analysis revealed that over 10 kb of mRNA was detected only in the ovary and a high amount of Vtg mRNA during oocyte growth was retained until spawning stage. In situ hibrydization demonstrated Vtg mRNA expression in the auxiliary cells closely associated with growing oocytes. The content of mRNA in the ovarian tissue cultured in vitro with CPG showed no change although the CPG extract enhanced Vn accumulation. A transcription and translation of Vtg mRNA were supposed to be regulated by the different mechanisms, respectively.

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Various genetic options for improving aquacultural strains are summarized and evaluated from the viewpoint of an individual aquacultural enterprise. Large scale national breeding programs, marker selection and bioengineering give transient economic benefits to “early adopters”, but, in the long term, will benefit mainly enterprises (farmers) who hold exclusive franchises or own part of the technology. Profits from increased productivity accrue primarily to technology developers, secondarily to the consuming public, and only marginally to farmers. On the other hand, proprietary improvement of a farmer's own broodstock gives a sustainable competitive advantage to individuals who can defend their ownership rights. Several low-investment (but not necessarily low-technology) procedures for developing strains on individual farms are described and illustrated by a hypothetical cash-flow model that gives a startling increase in the farm net profit (doubling after 5 years). Aquaculture would incorporate the technical benefits of modern genetics more rapidly, therefore, if scientists were to develop additional small-scale, low- and/or high-tech procedures that would enable farmers to capture the economic benefits.

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Despite its important role in providing livelihood for people in Asia, aquaculture has received only minor benefits from the implementation of genetic improvement programmes. Several strains of freshwater fish have been developed mainly by farmers with limited knowledge of genetic principles. This has led to the genetic deterioration of many of the farmers' stocks. Recently, a few genetically improved strains have been developed through implementation of genetic concepts. Novel strains of tilapia and rohu have been developed by selection, while cross breeding is more commonly used in common carp. The interspecific hybrid between the Thai walking catfish and the introduced African catfish has almost completely replaced the native catfish in aquaculture in Thailand. The prospect of implementing genetics for freshwater aquaculture development in Asia and considerations regarding genetic threats on aquatic biodiversity caused by aquaculture stocks are discussed in this article.

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At present, more than one hundred marine finfish has been examined for breeding and seed production in Asian Countries. Some species such as red sea bream Pagrus major, red snapper (Lutjanus spp.), flounder (Paralichthys olivaceus), groupers (Epinephelus spp., Cromileptes altivelis), sea bass (Lates calcarifer) and milk fish (Chanos chanos) are the most important species for mariculture. A large number of seed of those species have been produced for cage culture and marine ranching. Progress in marine finfish genetic and biotechnological research has been slow because of lack of knowledge on fundamental aspects of their biology. Research and development efforts aimed at improve the seed quality genetically are underway. Retarded growth, morphological deformities, increase incidence of diseases and mortality of hatchery produced seeds have been reported. The present paper is review of recent development in marine finfish breeding and genetic.

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A model fish is important for the experiment of fish genetics and breeding science. One of the role of model experimert in fish genetics is to perform the experiment which need long time in the commercially important fish. The guppy, Poealia reticulate, has been frequently used as model experimert of fish genetics, because of its many varieties and breeds, short life cycle, ease of breed and reproductive capacity.
In this review, inbreeding depression and genetic influence for the growth were considered. In the former problem, small number of parents leads the genetic drift and homozygotes of lethal recessive genes were observed And in I after problem, it was suggested that the small number of geves whichl ocate on sex-chromosome are influencing the growth in the guppy.

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This paper reviews the recent genetic studies of pearl oysters with reference to future perspective of pearl culture. Using hatchery technique, selective- and crossbreeding, and chromosome manipulation have been conducted. Traits studied were the size, shape and color of shells and maturation and spawning which are important for improvement in terms of production of pearls. Studies on classic breeding have provided the interesting results. Heritabilities of shell traits are rather high and useful for selective breeding in some traits. Chromosome manipulation has not provided stable results in triploid studies applicable to pearl culture with variable performance related to sterility. Primary cell cultures derived from several tissues have been made in pearl oyster. Information on molecular genetics has been scarce until recently. Genetic mechanism of pearl formation has been studied by cloning of cDNA related to mineralization of pearl substances and will be important for genomics assisted breeding. It is important to conserve the genetic diversity of the populations of each species of pearl oysters to respond to the various demands of farmers or consumers in future with regards to genetic resources.

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Abalone is one of the most important mollusca species in global for aquaculture, Technology for artificial seed production and a rearing system has been developed and established for the species. Specialized culture strains are expected. Genetic differences among species and local races have been analyzed by genetic markers for the purpose of introducing a new culture species. Heritability for growth has been calculated from the data of mating experiments for selective breeding. Chromosome manipulation techniques have been developed for the fixation of traits. We discuss the present and future of abalone culturing.

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Chromosome manipulation has been developed so as to develop a systematic technology applicable for genetic improvement of aquaculture species by combining with related techniques such as hormonal sex-control and conventional hybridization. This paper reviews current status of the monosex, sterile, allopolyploid and isogenic populations practically used in the aquaculture of salmonids. Chromosome manipulation would be promising, if it integrated with modem molecular techniques to promote genomics, transgenics and other biotechnology and then to develop more advanced system useful in future aquaculture.

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Large numbers of seed fish have been produced in both public and private hatcheries for stock enhancement programs and aquaculture of red sea bream, Pagrus major for several decades in Japan. Production increased to about 120 million seed fish in 1997. Artificial propagation using a small number of parental fish in hatcheries may result loss of genetic variation and increase of inbreeding that may induce negative effects on the genetic diversity and fitness of both hatchery stocks and wild populations. Since microsatellite loci provide co dominant DNA markers that are usually inherited in a Mendelian fashion and are hypervariable compared with conventional protein markers, microsatelilite polymorphism is expected to be an effective tool for studies on the genetic divergence of wild populations as well as for the broodstock management in aquacutture.
In this report, I review the researches on the genetic analysis of wild population and brood stock in red sea bream (Pagrus major) in Japan. The importance of population analysis with help of hypervariable DNA markers is emphasized in relation to the estimation of effective population sizes (Ne) and inbreeding coefficients (F) for the broodstock and seed fish. The paper also consideres procedures for managing and conserving the genetic diversity of the broodstocks and wild populations of red sea bream.

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