• Journal of fish pathology
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• v.35 no.1
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• pp.27-40
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• 2022

Yellow head virus (YHV), Infectious hypodermal and hematopoietic necrosis (IHHNV), Taura syndrome virus (TSV), and Infectious myositis virus (IMNV) cause serious mortality to Penaeidae shrimp in the aquaculture. In this study, YHV, IHHNV, TSV, and IMNV were surveyed from imported frozen shrimps between 2019 and 2020 via molecular diagnostic assay. Among 10 shrimp groups, YHV (n=1) and IHHNV (n=4) were detected by RT-PCR and PCR, respectively. From the phylogenetic analysis based on the partial ORF 1b region of YHV, YHV was classified into YHV genotype 3 (YHV3). And IHHNVs (n=2) detected from Litopenaeus vannamei belong to infectious IHHNV type 2. Although IHHNVs (n=2) identified from Penaeus monodon showed PCR positive results (MG 831F/R primer set), the sequences of ORF 2 and 3 were not amplified, suggesting that those samples might possess type A IHHNV related sequence of P. monodon. Furthermore, in the challenge test, even though PCR-detected isolates (YHV3/type A IHHNV related sequence or infectious IHHNV type 2) were not induced mortality to L. vannamei, viral genes were amplified suggesting that the viruses in the frozen shrimp could be non-pathogenic particles which are not enough to induce mortality.

• Fisheries and Aquatic Sciences
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• v.26 no.8
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• pp.470-481
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• 2023

Algal overgrowth in shrimp culture ponds can affect the quality of the aquatic environment, thereby adversely affecting the shrimp and causing economic losses. The objective of this study was to evaluate the variation in phytoplankton composition in intensive shrimp ponds in Bac Lieu province, Vietnam. Phytoplankton samples were collected in three black tiger shrimp (Penaeus monodon) ponds and three whiteleg shrimp (Litopenaeus vannamei) ponds. The collected data were analyzed using SPSS and canonical correlation analysis softwares. In total, 75 species of phytoplankton were recorded in black tiger shrimp ponds and 64 species in whiteleg shrimp ponds. Diatoms had the highest species diversity with 29-30 species (39%-47%), followed by green algae with 9-19 species (14%-25%); species numbers of other phyla varied from 5-12 (8%-16%). The total number of phytoplankton species throughout the study varied from 34-50 species. Algal density was relatively high and ranged from 497,091-2,229,500 ind./L and 1,301,134-2,237,758 ind./L in black tiger shrimp and whiteleg shrimp ponds, respectively. The diatom density tended to increase during the final stage of the production cycle in black tiger shrimp ponds. Blue-green algae and dinoflagellates also increased in abundance at the end of the cycle, which can affect shrimp growth. Diatoms were significantly positively correlated with pH, salinity, total ammonia nitrogen, and nitrate (NO₃^-) concentrations (p < 0.05). Blue-green algae and dinoflagellates were positively correlated with salinity, phosphate (PO₄^3-), and NO₃^-. Algal species diversity was lower in the whiteleg shrimp ponds than in the black tiger shrimp ponds. Several dominant algal genera were recorded in the shrimp ponds, including Nannochloropsis, Gyrosigma, Chaetoceros, Alexandrium, and Microcystis. The results of this study provide basic data for further investigations, and they contribute to the management of algae in brackish-water shrimp ponds.