Vol. 16 No. 10 (2018)

Swollen siphon disease has been considered as a serious threat to otter clam farming in Vietnam. Virus-like particles (VLPs) were identified asthe main causative agent of the disease, however, the transmission pathway and the pathogenesis of the disease has not been clarified yet. In this study, by using electron microscopy analysis, some host species such as otter clam spat and venerid clam (Tapes dorsatus) were selected to screen for the presence of VLPs and VLPs were further analyzed and described their size, structure and location in the host cells. The studies showed that VLPs were found in otter clam spat that were sampled from the hatchery. This finding indicated that the otter clam spat is one of the causes of spead of the wollen siphon disease in otter clam. VLPs have rod-like shape with the size ranging from 70-90 nm x 600-1.000 nm. They consist of outer shell, outer membrance, inner membrance, coreand are located in the cytoplasm of the host cells. Thesestudiesare playsed as scientific basis for developing strategies for classification of VLPs and control, prevetion and treatment of swollen siphon disease in otter clam.

A survey was conducted to assess variation of marine fishery resources in the Gulf of Tonkin from 2000 to 2015. The swept area method for demersal and near demersal fish groups and hydroacoustics method for pelagic fish group were used. The survey data on fishery resources conducted annually in the Gulf of Tonkin during 2000-2015 period revealed about 568 marine fishery species/groups belonging to 321 genera, 145 families, including demersal fishes (197 species), pelagic fishes (70 species), crustaceans (47 species) and squids (30 species). In 2000-2005 period, the total standing biomass (TSB) was estimated at about 453,000 tones and the maximum sustainable fishing yield (MSY) about 225,000 tones. From 2010 to 2015, the TSB was estimated about 752,000 tones and 719,000 tones, respectively, for the NE and SW monsoon seasons, and the estimated MSY was about 350,000 tones. Noticeably, the pelagic fishes accounted for about 70-80% of the MSY values while the figure for the demersal fishes was only about 20% in both periods.

A study was conducted to determine the changes in tannin,vitamin Candpolyphenolscontentsand antioxidant activity of the cashew apple juiceat different maturity stages.The cashew apples were collected in Binh Phuoc province and classified into 4 different maturity stages including: green (X), color turning (VC), ripe (CV) and over-ripe (CM). Results showed that the tannin, vitamin C and polyphenol contents of cashew apple juice decreased from 470±0.02mg/100ml, 334±3.7 mg/100ml and 1873±5.2 mg/100ml at green (X) to 130±0.01mg/100ml, 176±3.1 mg/100mland280±3.5 mg/100ml at over-ripe (CM), respectively. The antioxidant activity of cashew apple juice was determined basedon the IC50value of DPPH free radical scavenging method and the optical density value(OD) of reducing power method. The IC50 value of DPPH free radical scavenging capacity were 32.3±2.3 gdry matter/ml for green group (X), followed by VC (IC50 = 172.4±2.5gdry matter/ml), CV (IC50= 239.6±2.1gdry matter/ml) and CM (IC50= 407.1±2.1gdry matter/ml). Reductingpower of the cashew apple juices decreased during ripening of cashew apple in the order: X > VC > CV > CM. Thus, the contentsof tannin, vitamin Csndpolyphenolsand antioxidant activity of the cashew apple juice decreased also in the order: X > VC > CV > CM. The results suggestedthat the cashew apple in ripe (CV) and over-ripe (CM) maturity stage aresuitable to produce cashew wineorcashew juice.

Thepaper investigatespig production towardsfood safety in Luong Tai district, Bac Ninh province. Descriptive statistics, classification, comaprison and F test and Chi-squaretest are methods utilized to implement the study. It has been found that there is an improvement in some farming practices to reduce pig diseases and increase food safety in pork. For example, pig houses are designed well to mitigate the disease spreading from outside. Pig manure is treated by biogas and composting. In addition, piglet and feed are also well managed. However, there are certain practices that affect the spread of diseases and food safety including the treatment of inorganic waste in pig production in combination with domestic waste, the direct dischange of livestock wastewater into dranage system,selling and slaughtering sick pigs for home consumption. Recommendations for improvement of pig health risk to mitigate food safety risk in pig production in Luong Tai district are drawn accordingly.