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open access
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ISSN : 1225-3480
The Jugyo intertidal zone, located in Boryeong of Chungcheongnam-do Province on the west coast of Korea, is a well-known for natural seed production of the Manila clam Ruditapes philippinarum. In the present study, to understand the spatial distribution and density of natural seeds of wild Manila clams inhabiting this tidal flat, sediments were collected from 48 sites during mid-March in 2017 and 2018, and the density and size of the clams were measured. The collected clams were divided into five size groups (< 5mm, 5-10 mm, 10-20 mm, 20-30 mm, and > 30 mm). In addition, the clams were various ages, from spats measuring < 5 mm in length to those longer than 30 mm. In particular, during the 2017 survey, the densities of the five groups were comparable however, during the 2018 survey, over 90% of the individuals were spats of < 5 mm, whereas large individuals over 40 mm were not observed. Taken together, these results indicate that in the studied tidal flat, annual production fluctuates greatly, thus stable seed production should be induced through the continuous inhabitation of large individuals that serve as brood stock, as well as maintaining suitable sediment type.
In this study, commonly known as “starry night octopus” or “small-spot octopus”, Callistoctopus luteus (Sasaki, 1929), was newly recorded in Korea. This species is distributed in warm temperate oceans and is found at depths of up to 82 m. To data, 13 species in genus Callistoctopus have been recorded worldwide, but none have been reported in Korean waters. Herein, we provide the diagnostic characteristics with descriptions and pictures of C. luteus and with mitochondrial cytochrome c oxidase I (cox1) partial sequence.
The purpose of this study is to improve economical seed production of ark shell, Scapharca subcrenata by remote induced setting method. The setting rate according to the ark shell setting method differed from the set on net by 5.7% and high-density settlement system (Downwelling system) by ranging from 11.1-19.8%. Setting rate of high-density system was significantly influenced by initial stock in density were setting rate of high-density system was variable, at stocking density 30 × 104 individuals per setting aquarium with a setting rate 19.8%. however setting rates of between 60-90 × 104 individuals per setting aquarium were 13.8-11.1%, with higher density leading to higher setting rate. Using substrate in the high-density setting system, the setting rate was investigated and without substrate, microcultch 300 mL and microcultch 600 mL experimental condition with a non substrate condition was 17.2%, the microcultch 300 mL condition was 14.1%, the microcultch 600 mL condition 13.8%. The stimulation of increased setting rate by less substrate as microcultch, a situation beneficial to setting efforts for the species. As a result of investigating the new setting method of S. subcrenata artificial seeds, the hige-density setting method (Downwelling system) was able to produce 85 times higher per unit area than existing natural setting method, and it is expected that mass artificial seed production, S. subcrenata will be possible.
This study was conducted to investigate the influence of environmental factors such as water temperature, rearing density, food organism and feeding amount on the growth and survival of spat in surf clam, Tresus keenae. As a result of this study, the optimum conditions of spat rearing were as follows. The optimum range of water temperature is 22℃ to 25℃, the optimum rearing density is 500 ind./cm2 and the supply of mixed feed organism for spat rearing such as Isochrysis galbana, Chaetoceros simplex and Tetraselmis suecica is 50 × 104 cells/ml-100 × 104 cells/ml. The results of this study suggest that the optimum conditions of environmental factors in spat rearing of Tresus keenae contribute to productivity improvement through rapid growth and high survival.