<P> 본 연구는 해상가두리에서 양성중인 2년생 북방전복의 최적 사양관리 기준을 탐색하는 것이 목적으로 수용밀도, 먹이공급량 그리고 청소 빈도의 차이에 의한 전복의 성장과 생존을 조 사하기 위해 수행되었다. 실험에 사용한 가두리의 규격은 2.4m × 2.4m × 5.0m 크기였고, 12절 그물코를 사용하였으며, 전복의 평균 크기는 각장 64.7 ± 0.7 mm, 중량 38.3 ± 2.2 g 이었다. 사육 밀도는 가두리 1칸 당 800, 1,100, 2,000 마리였고, 먹이 공급량은 한 가두리 당 1.3, 2.0, 3.0, 6.0 kgㆍday<SUP>-1</SUP> 을 공급하였다. 가두리 청소 횟수는 1회ㆍmonth<SUP>-1</SUP>, 0.5회ㆍ month<SUP>-1</SUP>, 미청소 실험구였다. 실험종료 시 사육 밀도의 경우 가장 밀도가 높았던 2,000 마리 실험구의 무게 성장이 다른 실험구들보다 유의하게 낮았지만, 생존율에서는 차이를 보이지 않았다. 가두리 청소 빈도는 전복의 성장과 생존에 모두 영향을 미쳤는데, 성장은 한 달에 1회 청소하는 실험구에서 가장 높았고 생존율은 한번도 청소를 하지 않은 실험구가 가장 낮았 다. 먹이공급량 실험에서 2 kgㆍday<SUP>-1</SUP>와 6 kgㆍday<SUP>-1</SUP> 공급한 실험구들 사이에서 유의한 차이가 없었지만, 6 kgㆍday<SUP>-1</SUP> 공급한 실험구의 생존율이 유의하게 낮아졌다. </P>
The recent decline in Manila clam landings in Korean waters is, in part, linked to a high level of infection by the protozoan parasite Perkinsus olseni. In this study, we first surveyed the infection status of protozoan parasite P. olseni in the juvenile and small Manila clams using Ray’s fluid thioglycollate medium assay (RFTM). A total of 578 clams of shell length (SL) ranging 9.2 to 29mm were collected from 9 tidal flats in Gyeonggi Bay, the coast of Taean, Garorim Bay, and Gomso Bay in January and November 2008 and March 2010. The smallest clam (SL 9.2mm) of the survey was originated from Sungam in November 2008, which was infected by P. olseni with the infection intensity of 570, 000 cells/g tissue. RFTM revealed that the juveniles (10-15 mm SL) in Gomso Bay are infected by P. olseni with a mean infection intensity of 491,000 cells/g tissue, suggested that P. olseni infection in the juveniles can be initiated as early as a few months after the settlement. The juvenile (SL 20-25 mm) and small clams (SL 25-30 mm) in Hwangdo Island were heavily infected by P. olseni, with the mean infection intensity of 1.751 x 106 and 4.830 x 106 cells/g tissue, respectively. The survey confirmed that most of the juveniles and small clams in major clam beds on the west coast were infected by P. olseni, and it is believed that P. olseni infection is not limited to the adult clams.
The purpose of this study was to test the potential of digital PCR (dPCR) for diagnosing Perkinsus olseni. dPCR is currently one of the most effective molecular diagnosis techniques, as it is capable of quantifying the target sequence without a standard. Here, a primer pair and a probe were developed in the non-transcribed spacer region for diagnosis of P. olseni. In the sensitivity and specificity test, dPCR was able to detect as little as one P. olseni trophozoite, and could discriminate P. olseni from P. marinus. The number of P. olseni cells measured by dPCR was very similar to that determined by conventional cell counting. In conclusion, this study confirms that P. olseni can be quantified using dPCR. Additional validation is needed to access the efficiency of the technique in host tissues or environmental samples.
Growth and age of the Surf clam, Tresus keenae (Bivalvia: Mactridae) were collected from Yeosu coast in Korea. Relative growth equations among SL, SH, SW and TW of Tresus keenae were ranged from 0.8188 to 0.9468. The ring radius were estimated from a von Bertalanffy method with the values of SL1.54 = 44.72 mm, SL2.54 = 70.97 mm, SL3.54 = 91.57 mm, SL4.54 = 107.09 mm, SL5.54 = 122.86 mm. Back calculated total weight at the formation of annual ring on the shell of Tresus keenae with the values TW1.54 = 310.99 g, TW2.54 = 467.72 g, TW3.54 = 595.14 g, TW4.54 = 690.65 g, TW5.54 = 786.58 g. Growth curves for shell height (SH) and total weight (TW) fitted to the von Bertalanffy equation were expressed follows : SLt = 200.02(1 . e.0.1987(t + 0.14)) TWt = 1,711.93(1 . e.0.1987(t + 0.14))2.8225
The gonadal development, fatness index and spat recruitment of the marsh clam, Corbicula japonica were investigated by using both histological observations and population structure data. Specimens of C. japonica were collected from March 2017 to November 2018 in the Eulsuk tidal flat of the Nakdong River estuary, Korea. The mainly adult clams consisted of shell length 21 to 30 mm, and their density ranged from 8 to 32 ind./m2. The monthly density of Corbicula spats was very low and in the range of 0 to 22 ind./m2, and the highest density occurred in July 2017. Monthly variation of fatness index showed similar patterns to the variation of gonadal development. The sex ratio of male and female was 1:1.4. The gonadal maturity cycle of C. japonica could be classified into five stages according to its developing conditions with the ripe stage from July to August. From the results on gonadal development, fatness index and in-situ spat recruitment, the spawning season of C. japonica in the study area was estimated to be from July to September, and main recruitment might occur in August.
In this study, we examined influences of inland pollution sources on oysters (Crassostrea gigas) produced in Kamak bay. According to survey results, 3 sources of major inland pollution sources exceeded 1 km of radius of influence from January 2017 to December 2017. And from January 2017 to June 2019, the range of Fecal coliform, geometric mean and 90th percentile for 15 seawaters adjacent major pollution source were < 1.8-130 MPN/100 mL, < 1.8-2.3 and 1.8-7.3 MPN/100 mL. Also the range of Fecal coliform, E. coli and viable cell counts were < 18-790, < 18-230 MPN/100 g and < 30-850 CFU/g respectively. These results indicate that sweater and oyster of Kamak bay meets the standard of shellfish hygiene of Food Sanitation Act and assessed to be the Grade A. But some inland pollution sources affect Kamak Bay, so improvement or expansion of sewage treatment plant are necessary.
Laboratory exposure tests are helpful for specific clues between harmful algae and marine animals, but have a subject to be answered. That is if the cultured strains are as potent as the wild ones in nature. We tested damage potentials of cultured and wild strains of Cochlodinium polykrikoides to two aquaculture species, abalones Haliotis discus hannai and black scrapers Thamnaconus modestus at 26℃ for 24 hours in culture chamber (80 L) carrying each strain (50 L each) at around 2,000 cells mL-1 and two references, alga-free seawater and Tetraselmis suecica at 10 × 104 cells mL-1. The toxicities were species-specific. They were harmless to the abalone as were two controls. But both were acute to the fish with bigger potential of cultured one. In cultured strain, the fish reached mortality 40% at hour 0.25 and then total mortality at hour 2. The wild one was also damageable but less than cultured one with first and total mortalities at hour 2. All the findings were significant at least at P < 0.05. In the theory of allelochemical dynamics, dinoflagellate toxicity becomes more potent in nutritionally unfavorable waters. In our study, a conspicuous difference between the two strains was length of majority chain, 2-4 cells for cultured one and 8-16 cells for wild one. The shorter chain of cultured strain was reminiscent of the algal growth in less favorable nutrition and of higher production of allelochemicals, and thus might make it more toxic. Our estimation might be worth interpretation in exposure test of harmful dinoflagellates to marine animals.
This study was conducted to investigate the growth and survival rate of Haliotis discus hannai in sea cages due to differences in stocking density, cleaning frequency and seaweed supply amount. In the process of abalone aquaculture, the experiment was carried out to measure the management efficiencies according to the culture densities (800, 1100, 2000 seeds per cage), diet supply amounts (1.3, 2.0, 3.0, and 6.0 kg/day/cage), and cage cleaning cycles (once and twice per month). The sea cage used in the experiment was 2.4 m × 2.4 m. At the end of the experiment, the weight growth of 2000 stocking density was significantly lower than that of the other experimental groups, but the survival rate was not significantly different among the experimental groups. The frequency of cage cleaning affected both the weight growth and survival rate of the abalone. Weight growth was the highest in the experiment cleaned once a month and survival rate was the lowest in the experiments that had never been cleaned. In the diet supply amount experiment, there was no difference in weight growth between the 2 kg/day and 6 kg/day experimental groups, but the survival rate of the 6 kg/day group was significantly lower.
In the tidal flat oyster rack culture introduced in 2010, we investigated the parasitic infection from November 2015 to June 2017. The water temperature and salinity were ranged from 7.32℃ to 27.18℃ and from 27.6 psu to 32.7 psu, respectively. From the two serial growth experiments, commercial market sized oysters can be achieved within 18 months, one size group from the 2015 population with 88.67 ± 7.52 mm in shell length, 79.74 ± 13.33 g in total weight in August 2016 and, and the another from the 2016 population with 93.77 ± 12.11 mm in shell length, 78.99 ± 20.84 g in total weight in June 2017, respectively. Sex ratio represented at 1:1 ratio being closed to mature season but some intersex oysters were observed in immature period. Parasitic infection was ranged from 26 to 100% in prevalence and from 1.6 to 4.0 in intensity, which being associated with water temperature and gonad development index. Using the PNA clamping PCR, the parasite was identified as Apicomplexa which including Perkinsiosis pathogen in manila clam. There is no evidence which Apicomplexa can negatively affect cultural performance of oyster but more elaborated studies are necessary to maintain the sustainability of the rack oyster culture in Wando coast, Korea.
Domoic acid (DA) is a neurotoxin produced by the diatom genus Pseudo-nitzschia. This toxin is particularly problematic for bivalves that are cultured for human consumption. Scallops have especially low metabolic rates and readily accumulate toxins in their tissues. In this study, bay scallop were exposed to three concentrations of DA (20, 40, and 60 ng/mL) for 48 h, and immunological responses were investigated. Immune parameters were evaluated by estimating the levels of reactive oxygen species (ROS) in the hemolymph, and peptidoglycan recognition proteins (PGRP), fibrinogen-related proteins (FREP), and heat shock protein (HSP) 70 mRNAs in the digestive diverticula of bay scallops. Results showed that not only ROS but also PGRP, FREP, and HSP70 mRNA levels were elevated under exposure to high concentrations of DA. However, mRNA expression levels peaked at different times during exposure, with subsequent declines. Our results suggest that exposure to DA induce protein denaturation and damage, and bay scallops have insufficient defense to repair denatured proteins, owing to the toxicity of DA.
The invasive Caribbean false mussel, Mytilopsis sallei (Recluz, 1849) (Dreissenidae), established in Asia during the 20th and 21st centuries, is recorded for the first time in southern Vietnam in brackish-water Ba Tai Lake (Kien Giang Province). Colonies of this species were found in 2017, mollusks were attached to stones on the muddy bottom, at a depth of 0.3-0.7 m and salinity of 15-20‰, and water temperature of up to 35-40°C. M. sallei was not registered in Baс Lieu Province (Mekong Delta), in mangroves of the Red River Delta and Con Dao Archipelago during recent surveys (2017-2019) as well not known in regional literature; closest localities are southern Thailand and Hainan Island.
