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ISSN : 1225-3480
The influence of individual size, sediment, gain size, water temperature, salinity and air exposure on burrowing rate was investigated in order to obtain the basic biological data on applying shellfish farm for a sustainable production of ark shell, Scapharca broughtonii (Schrenk). The burrowing rate on individual size 300 minutes after starting the experiment was the highest in the shell length <TEX>$16.3\;{\pm}\;1.2\;mm$</TEX>, 97.7%. The highest burrowing rates were 97.0% in <TEX>$12.8\;{\pm}\;0.8\;mm$</TEX>, 96.7% in <TEX>$9.2\;{\pm}\;1.0\;mm$</TEX>, and 96.3% in <TEX>$5.9\;{\pm}\;0.7\;mm$</TEX>. The clams over 6 mm of shell length had burrowing ability and the burrowing rate was not related to the shell size. The burrowing rate depending on the kind of grain at the bottom after 300 minutes was the highest, 98.3%, in the mixture of sand and silt with a ratio of 75:25. The rates were 98% in silt (100%), 97.3% in mixture sand and silt with a ratio of 50:50, 97.3% in sand and silt ratio of 25:75, and 86.3% in sand (100%) in this specific order. On grain size of the soil in the seafloor, the burrowing rates after 300 minutes was at its highest in the group of sand in pore size 1 mm with 85.0%, and the <TEX>$12\;{\mu}m$</TEX> to 1 mm in the grain size was fitted to burrowing of artificial seed. In the case of water temperature, the burrowing rates were at its highest after 300 minutes. In <TEX>$30^{\circ}C$</TEX> group, the rate was 96.7% and in <TEX>$25^{\circ}C$</TEX> and <TEX>$20^{\circ}C$</TEX>, 90.0%. The rates decreased as the water temperature decreased below <TEX>$15^{\circ}C$</TEX>. The burrowing rates on salinity were the highest in 30 psu with 93.3% and at 15 psu and below, there was no noticeable change in the burrowing rate. On air exposure, the burrowing rates after 300 minutes were the highest in 1 hour with 93.3%, and remarkably decreased as air exposure time is longer after 12 hours of air exposure.
Data obtained from field observation revealed that the degree of shell bioerosion of the scallop, Patinopecten (Mizuhopecten) yessoensis, by endolithic organisms significantly higher on the muddy sand than on the sand. At the area studied, the polychaete worm, Polydora brevipalpa (=Polydora ciliata brevipalpa, Polydora ciliata Okuda, Not Johnston, Polydora variegata), which is common symbiotic species for the scallop made 95-100% of total scallop shell bioerosion at the area studied. The muddy bottom sediments enriched by organic matter create favourable conditions for development of microphytobenthos and bacteria, which are predominantly consumed by P. brevipalpa. Linear regressions for the degree of shell bioerosion on the scallop shell height, total wet weight and adductor muscle wet weight revealed negative relationships between them for the scallops inhabiting both sand and muddy sand. The influence of polychaetes on scallops is complex. They may be food competitors. Polychaete can directly affect the host through their boreholes. Scallop expends energy for shell regeneration to prevent the polychaete penetration into its interior cavity. It was found that the degree of shell bioerosion increased considerably with scallop age.
Samples of Potamocorbula ustulata ustulata were collected monthly from October 2004 to November 2005 in the Jujin estuary of Gochang, Chollabuk-do, west coast of Korean peninsula. Age of P. ustulata ustulata was determined by the rings on the shell. The relationship between the shell length and the ring diameter in each ring group was expressed as a regression line. Therefore, there is a correspondence in each ring formation. Based on the monthly variation of the marginal index (MI') of the shell, it is assumed that the ring of this species was formed once a year during October to December. The relationship between the shell length (SL) and the shell height (SH; mm) was highly correlated with shell height as the following equation: SH = 0.6438 SL + 0.5642 (<TEX>$r^2\;=\;0.978$</TEX>). The shell length (SL) - shell width (SW) relation was also expressed by the following equation: SW = 0.4352 SL - 0.5675 (<TEX>$r^2\;=\;0.957$</TEX>). Shell length (SL; mm) and the total weight (TW; g) followed: <TEX>$TW\;=\;6.999\;{\times}\;10^{-5}\;SL^{3.2542}(r^2\;=\;0.975)$</TEX>. Growth curves for the shell length and the total weight fitted to the von Bertalanffy's growth curve were expressed respectively as: <TEX>$$SL_t=30.77[1-e^{-0.4572(t+0.7371)}],\;TW_t=4.87[1-e^{-0.4572(t+0.7371)}]^{3.2542}.$$</TEX>
In order to estimate the ecological parameters of the population, short-necked clams, Ruditapes philippinarum, were collected from Jindu coast at Hansan Island, from April to December in 2005. The growth of the clam was estimated by von Bertalanffy growth model and each parameters were obtained from a nonlinear regression as <TEX>$L_{\infty}\;=\;48.8\;mm$</TEX>, k = 0.28 and <TEX>$t_0\;=\;-0.88\;(R^2\;=\;0.994)$</TEX>. Instantaneous coefficient of total mortality (Z) and fishing mortality (F) was calculated to be 0.8614/yr. and 0.6122/yr, respectively. The age at the first capture was estimated to be 2.88 year. Using the present parameter for clam fishing, the yield-per recruit (Y/R) was estimated to be 3.44g. Although the maximum Y/R was obtained under the parameters (<TEX>$t_c\;=\;3.48\;yr$</TEX>. and F = 0.9295/yr), it is favorable to maintain the current fishing effort considering the annual fluctuation of the parameters.
Population ecological parameters and stock biomass of the purplish washington clam, Saxidomus purpuratus (Sowerby), in the southern coastal areas of Korea were determined based on the fishery data from the Divers Fisheries Cooperative and other available biological data. Instantaneous coefficient of total mortality (Z) of purplish Washington clam was estimated to be 0.7479/year. The estimated instantaneous coefficient of natural mortality (M) was 0.2012/year. From the values of Z and M, the instantaneous coefficient of fishing mortality coefficient (F) for the recent years was calculated to be 0.4578/year. The age of purplish Washington clam at its first capture (<TEX>$t_c$</TEX>) was 2.7506 year. Yield-per-recruit and spawning biomass-per-recruit were estimated under harvest strategies that bases on <TEX>$F_{max}$</TEX>, <TEX>$F_{0.1}$</TEX>, <TEX>$F_{35%}$</TEX> and <TEX>$F_{40%}$</TEX> were shown as 81.60 g, 61.68 g, 115.07 g and 131.51 g, respectively. The acceptable biological catch (ABC) was estimated to be about 1,404 metric tons.
We investigated to understand the differences in the karyotypes and the reproductive characteristics between the diploid clam, Corbicula japonica in the brackish water and the triploid clam, C. fluminea in the freshwater. The number of chromosomes of the diploid C. japonica were 38, which can be grouped into 19 pairs of two homologues. These can be divided into 11 pairs of telocentric, 4 pairs of subtelocentric, 3 pairs of submetacentric and one pair of metacentric chromosomes. C. japonica is oviparous and dioecious. The clam has two pairs of gills, with the inner and outer-demibranchs, however, they do not act mainly as marsupia. External fertilization occurs in the brackish water. The triploid marsh clam, C. fluminea has 54 chromosomes, which can be grouped into 18 sets of three homologues. These 18 sets can be divided into one metacentric group, five submetacentric groups and 12 subtelo- or telocentric groups. C. fluminea is ovoviviparous and functional hermaphrodite. The triploid condition may be closely related to hermaphroditism. This species has the inner-demibranchs acting mainly as marsupia. The depletion of ripe eggs occurred in the inner-demibranchs of the gill during the incubatory periods, and ripe eggs produced in the hermaphroditic follicles in the gonad during the non-incubatory periods. The gonad developmental stages of two marsh clams (C. japonica and C. fluminea) can be divided into five stages: early active stage, late active stage, ripe stage, partially spawned stages, and spent/inactive stage.
This study examined the possibility on the dietary value and cryopreservation of the marine microalga, Isochrysis galbana. Four cryoprotectants, dimethyl sulfoxide (DMSO), ethylene glycol (EG), glycerol (Gly) and 1.2-propanedial (PD) were tested at the concentrations of 1.0, 1.5, 2.0, 2.5 and 3.0 M respectively. The highest survival rates were obtained with 1.5 and 2.0 M of four cryoprotectants yielding a survival rate of 80%. Cell concentration of <TEX>$30\;{\times}\;10^4\;cell/ml$</TEX> at the initial point of the experiment was increased to <TEX>$365\;{\times}\;10^4\;cell/ml$</TEX> in 1.5 M of dimethyl sulfoxide, <TEX>$298\;{\times}\;10^4\;cell/ml$</TEX> in 1.5 M of ethylene glycol, <TEX>$512\;{\times}\;10^4\;cell/ml$</TEX> in 1.5 M of glycerol, and <TEX>$385\;{\times}\;10^4\;cell/ml$</TEX> in 1.5 M of 1.2-propanedial after five days, respectively. In dietary value experiment, survival rate and growth were not significantly different.
The chromosome numbers and karyotype of Euphaedusa fusaniana, a kind of Korean land snail are investigated here. From E. fusaniana, chromosome numbers of 28 (n) and 56 (2n) were counted. Euphaedusa fusaniana has 15 pairs of metacentric chromosomes and 13 pairs of submetacentric chromosomes. The mean total length of all chromosomes was <TEX>$128.7\;{\pm}\;9.93\;{\mu}m$</TEX>. The maximum length of chromosomes No. 1 was <TEX>$9.6\;{\pm}\;0.21\;{\mu}m$</TEX>.
This catalogue is the result of a four-year survey of the mollusks of Jeju Island, the southernmost island in the Republic of Korea. Forty-eight survey stations were visited, with a total of 82 specific localities being sampled. Literature records were also obtained. Local and world distribution of each species is included. This survey reports a total of 1,072 mollusk species and subspecies; 1,015 marine and 57 land and freshwater. There are 812 gastropods, of which 755 are either entirely marine or have marine affinities. The best represented of the marine families are the Pyramidellidae, Trochidae, and Ovulidae. There are 225 bivalves, none being freshwater species, with the Veneridae, Mytilidae, and Arcidae having the largest number of species. Among the smaller classes there are sixteen Cephalopoda, eleven Polyplacophora, and eight Scaphopoda. Compared to mainland Korea, Jeju Island has a rather small terrestrial mollusk fauna and a depauperate freshwater one, with mainly Palearctic connections. The Helixarionidae and Bradybaenidae are the largest terrestrial families. The marine faunal affinities with the neighboring Japonic and Indo-West Pacific provinces are also discussed, revealing that this island's mollusk fauna is a blend of warm-temperate and subtropical-tropical species.
We have investigated introduced foreign molluscs into Korea since 1993. A total of 2,338 species of 157 families were investigated. Among them, 2,013 species of 106 families were gastropods, 307 species of 44 families were bivalves, nine species of two families were scaphopods, and nine species of four families in cephalopods. 2,128 species were newly given Korean name.
