Search

Post-thawed larval rearing in Pacific oyster Crassostrea gigas was performed to investigate the survival rate with time course in three kinds of larvae cryopreserved. The highest survival rate and larval activity index (LAI) of post-thawed larvae were obtained from the permeation in 0.2 M sucrose and 2.0 M ethylene glycol (EG) at -1°C/min in freezing speed showing the survival rates just after thawing of 63.8% in trochophore, 84.1% in D-shaped veliger and 56.3% in early umbo veliger. In post-thawed larval rearing with food supply, the larvae lasted their lives until 24 hours in trochophore, 75 hours in D-shaped veliger and 57 hours in early umbo veliger. The results suggested that each larval stage post-thawed revealed no more further development to subsequent respective stage.

The effects of photoperiod, temperature, and fish size on oxygen consumption (OC) in the black porgy Acanthopagrus schlegeli, a euryhaline marine teleost, were studied using a closed recirculating seawater system with a respiratory chamber. Fish reared in indoor recirculating seawater tanks were divided into two groups: small (15.7-55.8 g, mean 38.115.9 g) and large (108.7-238.8 g, mean 181.854.9 g) fish. The OC of the fish showed a clear diel rhythm, with higher values in the daytime and lower values at night, in accordance with light (09:00-20:59 h) and dark (21:00-08:59 h) cycles. The OC of the fish increased linearly with the water temperature. The OC was the highest at 10:00 h, one hour after the onset of daylight and was the lowest at 03:00 h, six hours after dusk. The average OC at during the light period was as high as 219.8 mg /kg/h in the small fish and 156.3 mg /kg/h in the large fish, while during the dark period it was as low as 130.5 and 110.4 mg /kg/h, respectively. The OC during the dark period, which showed limited variation, could be regarded as the resting OC, and was 107.6, 130.5, and 219.8 mg /kg/h at 15, 20, and , respectively, in small fish, and 52.3, 110.4, and 171.0 mg /kg/h in large fish. As the body weight of black porgy increased, the OC decreased exponentially and the relationship was expressed as OC=1,222.8, OC=1,113.2, and OC=1,495.3 at 15, 20, and , respectively. At a fish density of 14.5 g/L at , black porgy had the highest OC per breath compared to fish at the same density at 15 or . This suggests that the black porgy responds to the stocking density (15 kg/) and water temperature () conditions commonly observed in intensive aquaculture with the deepest breath and the highest metabolic activity.

Spawning induction, egg development and larval growth of ark shell (Tegillarca granosa) (L.) were investigated. The most effective method of spawning induction was steady temperature increasing from with irradiation of sea water by UV after T. granosa was exposed to air at Optimum condition for larval roaring was under the 32.4 psu and two temperature . Fertilized eggs was demersal isolated eggs, and egg diameter was . D-shaped larvae appear about 20 hr after hatching with in shell length and in shell height. Ten days were required from hatching to umbo larva stage, of a mean shell length . On 25th day, the larva grew to in shell length and began to settle on the bottom. Effect of temperature between (control group) and on larval growth was not different. Survival rate of larvae settled on the bottom was about in both temperatures conditions .

Gonadal development and gametogenic cycle of the equilateral venus, Gomphina collected in the coastal waters of Gangneung, Gangwon-do, Korea were investigated by means of histological method from March 2001 to February 2002. Sex of the clam was dioecious. The gonads are composed of a number of gametogenic follicles. The gonad index (GI) was reached the maximum in June (3.87), and the minimum in August (0.66). The condition index (CI) was reached the maximum in May (0.051), and the minimum in January (0.028). The gametogenic cycle of the clam could be divided into five stages inactive (September to November), early active (November to March), late active (April to May), ripe (June and July) and spent/degenerative stage (July to August). Sex ratio (male/female) was 1:0.9.

The gonadal development and the gametogenic cycle and the fine structure of ripe germ cells of the cultured Pacific oyster, Crassostrea gigas were investigated using oysters monthly collected from the southern coast of Korea from October 2000 to September 2001. Monthly changes in the condition index were similar to that of meat weight rate and the highest value was observed in between April and May, and the lowest value in August. The external colors of the testis and the ovary were milky white and yellowish, respectively. The spawning period of the Pacific oyster was continued from May to September, with a peak in July. The gametogenic cycle could be classified into five successive stages: multiplicative stage (December to March), growing stage (March and April), mature stage (April to June), spawning stage (June to August) and resting stage (August to January). Variety of egg yolk granules, lipid granules, mitochondria, and endoplasmic reticula were observed in cytoplasm of ripe oocyte. The spermatozoon consisted of the head, middle piece and tail; including cap-shaped acrosome with domed structure, elliptical shaped nucleus, four mitochondria, two centrioles and flagellum.

Ultrastructure of germ cell during gametogenesis of surf clam, Spisula sachalinensis were investigated by electron microscopic observations. Oogonia are oval in shape and 5-6 in diameter. They contain a large nucleus and have several mitochondria in the cytoplasm. Vitellogenic oocytes grew attached by a stalk to the germinal epithelium in the ovarian sac and their cytoplasm contained many yolk granules, lipid granules and mitochondria. Mature oocytes measuring 50-60 in diameter have a nucleus containing an electron dense nucleolus, and a lots of yolk granules, lipid granules, mitochondria, rough endoplasmic reticulum and cortical granules were present in the cytoplasm. The surface of the plasma membrane in mature oocytes was formed of microvilli approximately 1.5 long and enveloped in the vitelline layer. Spematogonia are oval in shape and about 5 in diameter. Sprmatogonia develop into spermatocyte, spermatid and spermatozoon. The spermatozoon consisted of the head, midpiece and tail. The sperm head with diameter of about 1.5 was ovoid, and contained the nucleus which consisted of acrosome. The four mitochondria encircled the centrosome in midpiece. The flagellum measuring about 40 long had the classical 9+2 axoneme structure.

We have experimentally evaluated the content of thyroid hormones (THs), the growth and activity of larval rockfish (Sebastes schiegeli) born from parturient mother fish injected with 20 g/g BW of 3,5,3-triiodo-L-thyronine (). There was no difference of L-thyroxine () levels between controls (sham control and control) and groups in yolk-sac larvae just born from broodstock, while level of group was significantly increased compared with controls. In addition, the both larval and levels in group were always higher than those of control during experimental period. Also, there were significant differences in the development of larvae from the two groups. The larval growth in total length and body weight according to the elapsed days after parturition showed the linear and curve equations, respectively, and the slopes of group were significantly higher than those of control. The survival rate of larvae in group was higher than that of control. Although the survival rate in group under the condition of starvation was significantly depressed compared with the control, larval swimming index in group was higher than control. Finally, these findings suggest that the exogenous could be transferred into hatched larvae in parturient rockfish by maternal injection, and subsequently the exogenous hormone could play some roles on physiological metabolism of larvae after parturition and may confer a distinct advantage to the fragile larvae during the early developmental stage.

Comparison of blood properties in juvenile black seabream (Acanthopans schlegeli) between transfer from seawater to freshwater (sFW) and transfer from freshwater to seawater (fSW) were investigated for 60 days. Plasma cortisol levels in sFW were significantly increased from 34.2 28.6 ng/mL at the beginning to 365.6 136.0 ng/mL at 3 hours, and decreased to the beginning level at 24 hours. However, in fSW, no significant differences in the cortisol levels were recognized throughout experimental period. No significant difference was found in the glucose levels between sFW and fSW. The transfer from seawater to freshwater of juvenile black seabream resulted in reduced concentrations for 24 hours (decreasing from 165.3 2.5, 146.0 2.2 to 118.3 12.3, 78.0 7.0 mEq/L, respectively), but these were completely recovered the beginning levels at 30 days. Total protein and AST showed no significant differences between the two rearing conditions, while ALT was markedly elevated at 3 hour in sFW and at 24 hours in fSW. Ht in sFW was increased from 18.5 at the beginning to 25.3 at 12 hours, and was decreased to the beginning level at 24 hours. Ht, RBC and Hb in fSW were also significantly higher at 12 hours, but recovered to their initial levels at 24 hours. All fish were dead until 50 days in sFW while survival rate in fSW was at the end of experiment.

The physico-chemical properties of fresh milt of marbled sole, Limanda yokohamae, brown sole, Limanda herzensteini, starry flounder, Platichthys stellatus and olive flounder, Paralichthys olivaceus among flatfishes, and the fine structure of their cryopresserved spermatozoa were investigated. The highest concentration of sperm among these four species was in marbled sole. Osmolality and pH of seminal plasma in four flatfish species were approximately 330 mOsm/kg and 7.6-8.1, respectively. Seminal plasma compositions showed interspecific differences. The sperm heads of marbled sole, brown sole and starry flounder were ellipsoidal and that of olive flounder was round. The numbers of mitochondria of these four species were eight in marbled sole, seven in brown sole and starry flounder, and six in olive flounder. Cross-sectional view of flagellum showed typical 9+ 2 structure in all species. Most of sperms cryopreserved with a proper method had no visible ultrastructural changes after freeze-thawing, compared with the fresh sperm, but in a few cases, swelling of their heads and midpiece regions were observed.

The proper conditions for cold storage of milt in four species of flatfish were investigated. Various diluents were tested for the preservation of marbled sole, brown sole, starry flounder and olive flounder milt at for 7 days. The most effective diluent was NaCl for marbled sole and Stein's extender for brown sole, starry flounder and olive flounder. After 7 days of storage in different dilution ratios (milt: diluent), marbled sole milt diluted with 1:3-10 and brown sole, starry flounder and olive flounder milt diluted 1:1-10 maintained good sperm activity index (SAI). SAI was affected by storage volume and presence of antibiotic. SAI was lower after 7 days storage in the volume of 1.5 mL than in 0.5 or 1.0 mL. SAI after 29 days storage was markedly enhanced by addition of antibiotic in marbled sole (400 ppm gentamicin, 400 ppm neomycin, 200-400 ppm streptomycin), brown sole (600 ppm gentamicin), starry flounder (1,000 ppm gentamicin) and olive flounder (200-1,000 ppm gentamicin, 200-400 ppm neomycin, 200-1,000 ppm streptomycin).

The ovary of the rockfish, Sebastes inermis was cystovarian condition and consists of numerous ovarian lobules. Previtellogenic oocytes were embedded in the connective tissue of the ovarian lobules. As the oocytes grows, it protruded into the ovarian cavity and form grapes cluster-like structure with egg stalk-like structure. Yolk granules and zona radiata were not observed in the embedded early oocytes about 20 m in diameter. In the oocytes about 80 m in diameter, yolk granules with electron dense were abundant in the ooplasm near the egg stalk-like structure. However, pinocytosis was not obsened in the pore canal system of the zona radiata. In this stage, microfilaments, developed endoplasmic reticula, tubular mitochondria, granular materials with low electron density and active multivesicular bodies were observed in the egg stalk-like structure. This results suggest that the egg stalk-like structure of the rockfish are related with the oocyte attachment and exogenous vitellogenesis of the intial vitellogenic oocyte.

In order to obtain the basic information for the seedling production of surf clam, Spisula sachalinensis, sperm motility and optimal method for fertilization were investigated. Sperm concentration of S. sachalinensis milt was and approximately of sperm showed forward movement after exposure to seawater. When sperm and eggs obtained by incision method were fertilized in 1 hour and 4 hours, respectively, high fertilization and hatching rate were achieved. The optimal sperm concentrations and egg density for fertilization and hatching were 10100 inds./egg and 100200 inds./mL sea water, respectively.