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ISSN : 1225-3480
For the health levels of the tidal flat and manila clam, (Ruditapes Philippinarum) in the west coast of Korea, the habitat characteristics of tidal flat and the biomarker genes of manila clams were investigated. Surface sediments and manila clams were collected from eight site of west coast of Korea, they were examined the geochemical characteristics and manila clams were analyzed the Poly Aromatic Hydrocarbons (PAHs) and heavy metals and the total RNA of these meat part with RT-qPCR method. Total RNA such as heat shock protein 70 (Hsp70), heat shock protein 90 (Hsp90), glutathione S-transferases (GST) and thioredoxin (TRX) was extracted from the meat part of the collected clams. Expression of the genes was analyzed by PCR method and the expression of biomarker genes were changed in the eight sites analysis areas. These results indicate that biomarker genes can be used to assess the condition of the environment. That is related to stress, immune and antioxidant related genes. Results showed that the expression of biomarker genes were changed in the eight sites and were relevant with the heavy metals and PAHs concentration of sediments, respectively. We suggested that biomarker genes were impressed an important role for the health level assessment of tidal flats.
Recirculating aquaculture systems (RAS) can improve the production of farmed abalone, but there are issues with using such systems. An important issue is that the health of shellfish reared in such systems is largely determined by feed type. Therefore, it is important to optimize diets to improve the production of abalone. In this study, Haliotis discus hannai in a recirculating aquaculture system were fed with three types of dry seaweed Saccharina japonica, Undaria pinnatifida, and Pyropia tenera) together with formulated diet (FD) in five different ratios. The different feed treatments were run for 90 days to examine the effects on abalone growth. The highest growth rate was 12.35%, which was observed for shell length in the group fed Pyropia tenera, with 7.01 and 7.14% growth rates in the groups fed Undaria pinnatifida and formulated diet, respectively. A 3.36 % growth rate was observed in the group fed Saccharina japonica alone. However, the addition of appropriate proportions of seaweed to the mixed diet led to better growth, indicating protection against the nutritional deficiencies of FD. The CaCO3 abalone shell mainly comprises aragonite and calcite. Rearing in RAS and natural seawater resulted in 7:3 and 6:4 aragonite to calcite ratios, respectively, with no feed type-based difference. We, therefore, speculate that shell composition is influenced more by the environment than the feed in that the metastable aragonite crystal structure is converted to a stable calcite crystal structure in natural seawater, where minerals are abundant.
In Korea, Longline oyster farms are located near shipping routes, where continuous artificial waves are generated by the movement of ships, causing physical stress, known as the "tumbling" phenomenon, which has been reported to result in reduced growth. Therefore, to develop suitable suspended cutchless oyster farming techniques in the korea, the relationship between physical impacts and the growth of suspended cutchless oysters was investigated. The oysters in the 0 m and 1 m experimental groups showed higher growth in terms of condition index and flesh weight in April compared to other groups. Cutchless oysters in the suspended group exhibited relatively higher whole and flesh weights throughout the period, confirming faster growth compared to hanging cultured oysters. Shell height growth was recorded in the following order 3 m depth group, 1 m depth group, hanging cultured oysters and the 0 m depth group. This slow growth in the 0 m depth group appears to be due to damage to the shell edges caused by physical impacts. However, whole weight was similar in both the 1 m and 3 m depth groups, with the 0 m depth group showing relatively lower growth, apparently due to physical stress. This study confirmed shell edge damage and partial growth retardation of individual suspended oysters caused by physical impacts as a function of depth.
Tetrodotoxin (TTX) is a potent neurotoxin commonly found in pufferfish and various marine invertebrates. Previous studies conducted in southern Taiwan and Japan have reported that species within the genus Umbonium, a group of marine trochid snails, act as vectors for TTX. Although these trochid snails are also commonly found on sandy or muddy tidal flats along the west and south coasts of Korea, no studies have yet investigated the presence of TTX in these snails. In this study, we screened U. costatum, a species widely distributed along Korea's west and south coasts, for the presence of TTX. In 2023, we collected U. costatum specimens from Myeongsa Beach on the south coast and Seonyudo Beach on the west coast, and analyzed their tissues for TTX using a competitive enzyme-linked immunosorbent assay (cELISA). The cELISA results indicated that TTX concentrations in the tissues of all collected snails were below the detection limit. Based on these findings, it appears that U. costatum from the west and south coasts of Korea may lack the capacity to accumulate TTX, or the absence of TTX may be due to the lack of TTX-containing prey in their environment. However, further investigations, including monthly toxicity screenings and studies on the TTX tolerance capacity of U. costatum, are needed to understand TTX dynamics in this species better.
Previous studies have shown that the apicomplexan protist Perkinsus olseni induces both sublethal and lethal effects on the Manila clam (Ruditapes philippinarum) along the west and south coasts of Korea, including Jeju Island. In this study, we assessed the prevalence and infection intensity of P. olseni in Manila clams from sand beaches on Jeju Island in July 2022, using Ray's fluid thioglycollate medium assay (RFTM) and histology. Condition index (CI) as the proxy of the fitness of clams (i.e., the ratio of dry or wet tissue weight to the shell weight) collected in July 2022 ranged from 74.5 (Jongdal-ri) to 122.9 (Segwipo), or 0.27 (Moseulpo) to 0.62 (Segwipo). The mean infection intensity, measured as P. olseni cells per gram of gill tissue in clams collected from six sites, ranged from 0 (Geumneung, Gimnyeong, and Moseulpo) to 56,000 cells/g of gills (Seongsan), with prevalence rates (i.e., the percentage of infected clams) ranging from 0 to 47%. Similarly, infection intensity in total tissue ranged from 0 (Geumneung and Gimnyeong) to 47,870 cells/g of tissue (Seongsan), with prevalence rates between 0 and 83%. Histological analysis corroborated these findings, revealing low infection intensity, with infection scores ranging from 0 to 1.0 across the six sites. Despite rising sea surface temperatures in Jeju Island over recent decades due to global warming, P. olseni infection prevalence and intensity appear to have remained stable. The low density of Manila clams in Jeju Island may partially explain the observed low infection intensity and prevalence.
