While Suminoe oyster Crassostrea ariakensis (Fujita, 1913) occurs widely in subtidal estuaries on the south coast of Korea, few studies have reported their reproduction. In the present study, we estimated reproductive effort of female Suminoe oysters from Seomjin River estuary on the south coast of Korea during spawning and post-spawning. Gametogenic condition was assessed using histology and reproductive effort and/or fecundity was determined using an indirect enzyme-linked immunosorbent assay (ELISA). Histology revealed that at Seomjin River estuary in 2008, the females spawned mostly in August and September. Gonad somatic index (GSI, the reproductive effot) of the female in ripe stage was estimated as 0.346, which was equivalent to 108 million eggs. The potential fecundity of Suminoe oyster determined in this study was smaller than the fecundity reported previously from the same sampling site (162 to 910 million/oyster), possibly due to size of the oysters used in the analysis.
The alleged Karenia mikimotoi involvement in Haliotis discus hannai mass mortality has been controversial as the low toxicities might not be consistent with the mortalities. Laboratory test might be a likely approach to explain the inconsistence. Tested were a series of exposures of K. mikimotoi (KM02 KSS) concentrations (0, 5, 10, or 20 x 103 cells ml-1) to adult H. discus hannai at 5 temperatures: 3 for 23, 26, and 28℃ during increasing period (23A, 26A, 28A) and 2 for 28 and 26℃ during decreasing period (28B and 26B). K. mikimotoi damage was highly temperature-dependent. Of 5 temperatures, 28A was the single damage inducer. The abalone mortality at 28A appeared to be due to loss of physiological strength caused by temperature itself, which was evidenced by increased mortality of abalones growing at the same condition in the commercial farm from which abalones were sampled for each exposure. Control mortality (15%) at 28A also endorsed the estimation. Cochlodinium polykrikoides (NIFS CP001) damage was viewed at lower temperature or when the abalones were still strong enough, suggesting the algal damage potential might be bigger than K. mikimotoi. Findings from K. mikimotoi together with those from C. polykrikoides suggest that K. mikimotoi damage potential to the abalones might be minor or inconsistent with the alleged mass mortality of the abalone.
Owing to limited production of juveniles, Manila clam (Ruditapes philippinarum) aquaculture in Korea has increasingly relied on imports of juvenile Manila clams from China. This study compared survival and physiological status of domestic and imported juvenile Manila clams. Domestic juvenile Manila clams were collected from Boryung, Chungnam Province, Korea, while imported juveniles were purchased from a trader who imported juvenile Manila clams. Clams of similar sizes were selected, and sown in clam cages installed in Gomso Bay, on the west coast of Korea. The mortality rate, growth, infection, reproductive cycle, and physiological response were monitored monthly from April 2015 to February 2016. Higher mortality and low immune parameters with higher pathogen infection rate were observed for imported clams compared to domestic clams during the experiment. It was hypothesized that the high mortality and low physiological status of imported clams might be caused by high levels of stress during the long period of transportation. High level pathogen infection in imported clams suggests that quarantine procedures should be consolidated to prevent the import of new diseases to the seas around Korea.
In order to understand the gene expression of the Pacific oyster, Crassostrea gigas, during the early development stage of fertilized egg, transcriptome analysis was carried out to identify the embryogenesis-related genes from mRNA of each stage of embryo such as pre-fertilization-, fertilization membrane-, and polar body release-stage, respectively. Specifically expressed genes identified MYC, CDC25B, CCNB1, CLN3, DMC1, ADCY2, ADCY6, FBXO5 in prefertilization-stage, GRR1, CLB3_3, FBXO43 in fertilization membrane-stage, and BUB1B in polar body release-stage, respectively. A quantitative analysis of gene expression identified 6 candidates for embryogenesis regulation genes including PPP1CB, AUR, CDC25A, SLK, NCAPD2 and Hsp70 in the early stage of embryo development. These genes should be useful markers for further studies for gene regulation of polyploidy embryo development.
This study compared that the nutrient composition of two domestic commercial Yesso scallop (Korea: Gangneung hanging culture, Pohang sowing culture) and one imported commercial Yesso scallop (Japan: Hokkaido sowing culture), which are distributed on the east coast of Korea, for increasing their value and efficient utilization. The crude lipid content of carcass was 0.11-0.32%, the lowest among the proximate composition. A total of 18 amino acids were identified, the glutamic acid was the highest content of 13.9-14.6% of the total amino acids. A total 27 free amino acids were identified, free glycine content was highest at 34.3-42.9% of the total free amino acids. Eicosapentaenoic acid (EPA, C20:5n-3) and docosapentaenoic acid (DHA, C22:6n-3) content of Gangneung hanging culture scallop were highest at 326.2 ± 38.04 mg/100 g and 195.7 ± 23.10 mg/100 g in total fatty acids of scallops, respectively. Vitamin B2, niacin, sodium, potassium and magnesium content were significantly affected by habitats. Based on these results, each nutrients composition was affected by habitats and culture method. However, all Yesso scallop used for analysis were low fat seafoods and considered to be high-quality food rich in EPA and DHA.
This study was carried out to investigate the effects on the occurrence of clam spats resources by sand supplement and plowing at the natural seedling fields of manila clam (Ruditapes philippinarum) in Geunso bay, Taean-gun, of the west coast of Korea. The sand addition and plowing were conducted on the tidal flats of Pado-ri and Beopsan-ri in Geunso bay in August 2013. We monitored the variation of newly recruited clam spats (shell length (SL) ≤ 5 mm), adult clams (SL ≥ 10 mm) and the change of sediment from January 2014 to December 2015. In the Pado-ri tidal flats (with 2-4 hours mean air-exposure time), the density of newly recruited clam spats in the experimental site (sand added) was higher 1.5-4.0 times than that of control (sand not added) from October 2014 to April 2015. And the highest clam density was 25,750 ± 1,708 clams per square meter in January 2015. The density of adult clams in Pado-ri was also higher in the experimental site than control until June 2015. However, despite lots of juvenile clams (SL ≤ 20 mm) were observed in control site, adult clam density in Pado-ri has changed from July 2015 due to decrease of sand proportion in sediments. In Beopsan-ri experimental site (with 4-6 hours mean air-exposure time), the newly recruited clam spats was less than 3,000 clams per square meter, which was lower than control. As the results of the study, it seems that clam spats increased by sand addition and plowing are likely to be decreased in a short period of time due to deposition of fine sediment and other adverse environments (such as long air-exposure time). Therefore it seems to be necessary to examine carefully the various environmental factors before trying to improve the environment of natural clam seedling beds by sand supplement and plowing.
Imports of aquatic products continue increasing every year. When imported into Korea, the common name of a similar aquatic product is used instead of a scientific name, causing many confusions. In this study, in order to cope up with this issue, four countries with the highest number of imported bivalves were selected. The collected bivalves were totally classified into 10 orders, 17 families, 39 species. Also, the collected bivalves in the current study were identified by morphological classification. Moreover, sequence analysis of COI gene was carried out for all the collected species. The COI gene sequence was obtained with 3 type of primers. All COI sequences analyzed were subjected to molecular phylogenetic analysis. As a result, it was possible to draw conclusions very similar to the morphological classification results. Taken together, it is preferable to perform the universal primers and the lobo primer simultaneously for analyzing the COI sequence of bivalves. On the other hands, to obtain the results for scallops, the Matsumoto primers were available to conduct the analysis.
The bivalve molluscan fauna of Jeju Island (Jeju-do), the largest island of Korea, is reviewed based on original and literature data. An annotated and illustrated catalogue of species with indication of local distribution and taxonomic comments is prepared, supplemented also with data on general distribution, habitats, and primary synonyms. This first part of the paper includes 105 species belonging to 21 families (Nuculidae through Limidae). The history of Jeju molluscan research, a bibliography on all aspects of mollusk biology, and the general ecology of Jeju bivalves in various habitats are also included. Five species are reported as new for Jeju Island, two species as new for Korea, and 11 species have been reported in literature but were not included in the first bivalve catalogue of Jeju by Noseworthy et al. (2007); in total 16 species are added to the fauna.