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ISSN : 1225-3480
Distribution, population structure, and growth of the bivalve Protothaca euglypta were investigated for clams collected from the northwestern part of the East Sea of Russia. This species is distributed in further northern area than it was found earlier. In the southern area, this clam is found in the intertidal zone, up to 8 m in depth. It is one of the most numerous infaunal species of bivalves, and protected to wave action in the gravel-pebble and sand with rubble biotope. Population density of P. euglypta reaches 500 <TEX>$spc./m^2$</TEX>, and biomass 2 <TEX>$kg/m^2$</TEX>. Size and age composition of the local settlements and allometric growth of P. euglypta depend on a biotope. The growth rate of P. euglypta considerably reduces in case of the northern boundary area, whereas life span increases.
A new species of the mytiloidean freshwater bivalve is described from Baengnyong Cave, Pyeongchang-gun, Gangweon-do. Limnoperna coreana n. sp. belongs to the genus Limnoperna Rochebrune, 1882 with the byssus. This species has a small shell with the glossy surface and rounded-triangular and differs morphologically from all of its congeners.
The Korean freshwater Sphaeriid clam species, Pisidium(Neopisidium) coreanum is re-described and illustrated, based on the type locality specimens. Authors considers that original description of this species is by Kwon, Pisidium(Neopisidium) sp. in 1990.
The gonad index, reproductive cycle and first sexual maturity of Sinonovacula constricta collected from Simpo, Kimje-gun, Korea were investigated by histological analysis. The gonad index(GI) in both sexes of S. constricta increased from April and reached a maximum in July when the water temperature rapidly increased. And then, the GI values gradually decreased by spawning from August through October. Monthly variations in the GI showed a close relationship with ovarian development. The reproductive cycle in females and males can be classified into five successive stages: early active stage(March to June), late active stage(May to July), ripe stage(July to September), partially spawned stage(August to October), spent/inactive stage(October to March). The percentage of first sexual maturations in female and male clams of 50.1-60.0 mm in shell length was over 50%, and for clams over 70.1 mm in shell length, it was 100%. Because harvesting clams < 50.1 mm in shell length could potentially cause a drastic reduction in recruitment, a measure including a prohibitory fishing size should be taken for adequate improved fisheries resource management.
Two trochid shells of the genus Ginebis, G. crumpii(Pilsbry, 1893) and the genus Enida, E. japonica A. Adams, 1860, collected from the coast of Jeju Island in Korea are reported. Ginebis crumpii and Enida japonica are closely related to Calliostoma Swainson, but can be differentiated by the features of the aperture and umbilicus. These species are a new records to the Korean Molluscan fauna. At present, G. crumpii and E. japonica are the only species of the represented in Korean water. Including the new records in this study, the family Trichidae contains 30 genera and 57 species in Korean water.
In order to investigate the possibility of yearly-harvest, we carried out growth experiment(shell height, meat weight and condition index) for of the artificial oyster spat, which suspended in three different times before the season for natural spat around coastal waters of Gyeongnam Province. Shell growth of spats suspended in June showed higher than those in April and May. In meat weight, the growth of spats was significantly elevated from October, of which significant difference was observed depending on growing farms(Gosung<Tongyeong and Koje). Using condition index, we found that the spat deployed in April and May were spawned on August or September, however, could not that in June. The estimated yield time were accounted for September on the shell height level(<TEX>$\geq$</TEX>80 mm) and October on the meat weight level(<TEX>$\geq$</TEX>5 g).
In other aquaculture species, large improvements in growth have been achieved through selective breeding. Ezo abalone(Haliotis discus hannai) and disk abalone(H. discus discus) are major aquatic animals cultured in Asia, but selective breeding for the promotion of growth with these abalones has not been actively pursued. Recently significant efforts are being made to promote production of these species through selective breeding in Korea. The aims of this work were to estimate the general genetic parameters, heritabilities, and genetic and phenotypic correlations on growth-related traits at 1-year old in two Korean abalone subspecies, H. discus hannai and H. discus discus, by using multiple trait animal model. The data were collected from the records of 1,504 individuals produced from 22 sires and 26 dams in H. discus hannai and 297 individuals produced from 5 sires and 6 dams in H. discus discus, which evaluated by the Genetics and Breeding Research Center, National Fisheries Research & Development Institute(NFRDI). Genetic parameters were estimated for these abalone subspecies raised in Bukjeju branch, NFRDI, from May 20, 2004 to May 16, 2005, respectively. The heritability estimates obtained from restricted maximum likelihood(REML) were higher than expected, ranging from 0.40 to 0.43 for growth traits shell length, shell width and body weight in H. discus hannai and from 0.26 to 0.51 in H. discus discus, respectively. The heritabilities for shell shape and condition factor were lower than others of growth traits such as ranging from 0.09 to 0.19 in H. discus hannai and from 0.10 to 0.23 in H. discus discus, respectively. Genetic and phenotypic were > 0.93 between shell parameters and weight in two abalone species, respectively, indicating that breeding for weight gains could be successfully achieved by selecting for shell length.
Growth and survival of the spat of arkshell, Scapharca broughtonii were investigated for the improvement of survival in intermediate culture with different shape of protective net and type of preventive net of spat loss. The growth performance of the spat of arkshell was observed for 60 days by using different forms of protective net, as the exposure form with an average shell length of <TEX>$12.8{\pm}3.2$</TEX> mm(P<0.05), the fish pot form with <TEX>$12.2{\pm}3.5$</TEX> mm, the cylinder form with <TEX>$11.9{\pm}3.8$</TEX> mm and the last one is the rectangular form with <TEX>$10.9{\pm}3.7$</TEX> mm. Their numerical value did not show any marked difference with each other. But in case of survival rate, the fish pot form showed highest survival rate which is 43.7% and the significantly lowest was showed by the exposure form, which is 5.4%(P<0.05). The cylinder form and rectangular form showed 41.2 and 31.6% respectively. And then the growth of the spat of arkshell was observed for 163 days by rearing in a sort of preventive net, the first group was in a blackout curtain with average shell length of <TEX>$13.9{\pm}3.1$</TEX> mm, the next group was in a balsam pear net with <TEX>$12.9{\pm}3.0$</TEX> mm, in a polyethylene net with <TEX>$11.8{\pm}3.1$</TEX> mm and the control with <TEX>$12.6{\pm}3.3$</TEX> mm which was not installed by preventive net of spat loss. The survival rate was 91.5% in a blackout curtain, 90.1% in a polyethylene net, 88.5% in a balsam pear net and 61.5% in a controlled group. It is seen that the highest growth and survival rate were observed in a fish pot form and cylinder form. These results were a little bit difference from those of the spat of arkshell cultured in the form of different preventive nets. There was no significant difference in survival rate in relation to the sorts of preventive net against carrying-away, but there was a difference in survival rate by more than 30% as against the non-installed controlled group. We expect that survival rate would be highly improved in intermediate culture carried out with fish pot form and cylinder form of protective net and preventive net of spat loss.
Growth and survival rates dependent on the density of a pen sell, Atrina pectinata were measured from Duekryang bay in Korea. Annual water temperature and salinity of the study area were ranged from 14.5 to <TEX>$28.0^{\circ}C$</TEX> and from 27.98 to 31.89 psu, respectively. The pH, DO, COD, DIN, Chl-a and SPM in the study area ranged from 7.78-8.35 mg/L, 7.07-7.90 mg/L, 1.20-1.70 mg/L, 2.88-6.02 mg/L, 0.20-0.79 mg/L and 10.8-21.4 mg/L. The IL, COD and AVS in sediments ranged from 4.0-4.6%, 7.28-10.76 mg/L and 0.03-0.05 mg/L respectively. The daily growth rate of shell height and total weight were 0.27%, 0.33%(5 indiv./<TEX>$m^2$</TEX>), 0.26, 0.29%(10 indiv./<TEX>$m^2$</TEX>) and 0.21, 0.20%(35 indiv./<TEX>$m^2$</TEX>). The survival rate also decreased along the density gradient; highest at the lowest density of 5 indiv./<TEX>$m^2$</TEX> and lowest at the maximum density of 35 indiv./<TEX>$m^2$</TEX>.
We studied the management policy for Haliotis diversicolor fisheries in the coastal area of Sungsanpo using Yield-per-recruit model from 2004 to 2006. The age at first capture(<TEX>$t_c$</TEX>) and fishing mortality(F) annually estimated during the study period decreased and increased, respectively. The maximum yield-per-recruit in 2004 was increased by increasing <TEX>$t_c$</TEX> from the 2.012 year of current <TEX>$t_c$</TEX> to 2.7 year or increasing F from the 0.574/year of current F to 0.800/year, and that in 2005 was increased by increasing <TEX>$t_c$</TEX> from the 1.946 year of current <TEX>$t_c$</TEX> to 2.5 year or increasing F from the 0.578/year of current F to 0.880/year. In 2006, the maximum yield-per-recruit was increased by increasing <TEX>$t_c$</TEX> from the 1.926year of current <TEX>$t_c$</TEX> to 3.1 year or decreasing F from the 1.088/year of current F to 0.810/year. Further, although the current F in 2004 and 2005 was lower than the estimated <TEX>$F_{MAX}$</TEX>, that in 2006 was higher than the estimated <TEX>$F_{MAX}$</TEX>. These results indicate that the likelihood of growth overfishing with increasing catch of smaller H. diversicolor in 2006 was greater than in 2004 and 2005. As action that could prevent growth overfishing in fisheries management of H. diversicolor, increasing for the current <TEX>$t_c$</TEX> could be a more appropriate policy because the artificial decrease of the number of woman divers related F is actually difficult.
We investigated artificial mass seed production of a Chinese scallop, Patinopecten yessoensis, in 2004. The GSI(gonad somatic index) of the Chinese scallop, P yessoensis was 17.2 on mid-February, 20.2 on mid-March, while that of Korean scallop, P yessoensis was 6.9 on mid-February, 10.8 on mid-March. Matured 120 females and 350 males were selected for artificial mass production. They were exposed in air for 1 hr at over <TEX>$20^{\circ}C$</TEX>, and placed into a spawning tank(20 ton) containing sea water treated with UV radiation at <TEX>$12^{\circ}C$</TEX>. We gained a total of 228,000 thousand scallop embryos between March 10th and 15th, and reared larvae at the indoor tank during 25 days. When the mean shell length of larvae reached 250 <TEX>${\mu}m$</TEX> and they have eye-spots, the number of pre-settling larvae was 47,500 thousand. We gained 1,850 thousand attached scallop spats from two kinds of collectors. Attached spats were reared in indoor tank for different periods from 5 days to 60 days. They were divided into 5 groups according to the length of reared days. Each group of attached spats was moved to intermediate rearing sites at Yangyang fishing port in Gangreung-city for acclimation to ocean environments. The highest survival rate of attached spats was 13.0% shown at the group reared for 12 days, but the significant difference in their growth was not found between the groups. The shell length of artificial attached spats increased from 0.9 <TEX>${\mu}m$</TEX> on July 10th to 24.7 <TEX>${\mu}m$</TEX> on December 16th with the survival rate of 85.0% while that of natural attached spats increased from 0.6 <TEX>${\mu}m$</TEX> on July 10th to 23.9 <TEX>${\mu}m$</TEX> on December 16th with the survival rate of 85.7%.
