No abstract

The population dynamics of eight commercial species of shrimp (Haliporoides sibogae, Harpiosquilla harpax, Metapenaeus affinis, Metapenaeus brevicornis, Metapenaeus tenuipes, Parapenaeopsis cultrirostris, Parapenaeopsis gracillima and Parapenaeus maxilipedo) distributed in littoral marine zone of the Mekong Delta were investigated. Length-based stock assessment using FiSAT II software package was used to assess the growth and mortality parameters: Asymptotic size (L8), growth coefficient (K), total (Z) and natural (M) mortality, exploitation rate (E), recruitment pattern, current probability of capture and selectivity of fishing gears. Yield-per-recruit analyses were carried out showing different levels of the exploitation. Results showed that the maximum sustainable yield would be reached for an exploitation rate higher than the current one for each population. However, the size of first capture should be increased for every population. The findings indicated that the current exploitations of shrimp populations distributed in littoral marine zone of the Mekong Delta are under exploitation level for maximum sustainable yield; however, all the shrimp populations are subject to growth over-exploitation.

Pancreatic ribonucleasc and sucrose (ribonuclease-free) were purdiased from Schwarz/ Mann (Orangeburg, NJ). Ribonucleases S and N, bacieriophagc MS2 and Esdjeridjia coli iRNA and rRNAs were obta ned from Miles Laboratories (Elkhart, IN). Pronasc was supplied by Calbiodiem (Los Angeles, CA), and proteinase K was obtained from EM Laboratories (Elmsford, NY). All other enzymes were purdiased from Wonhington Biochemical Corporation (Freehold, NJ).SBMV virions (bean strain) were propagated in Phaseolus vulgaris h. 'Bountiful' and purified according to Hsu, SEHGAL and PICKETT (1976). SBMV-RNA was isolated and purified by the procedure of Hsu, WHITE and SEHGAL (1977). Infectivity assays were performed on the primary leaves of P. vulgaris 'Pinto' (SEHGAL 1973a). Virions (2-3 mg/ml) were treated (5°C, 1 h) with EDTA (15 mM) dissolved in 0.1 M sodium phosphate buffer, pH 7.5. All enzyme treatments were done at 5 ^C for I h.The following procedure was used in removing nueleases from the treated virions prior to RNA extraction. To the virion suspension, sucrose (3 %) was added and this sample (2.5 ml) was layered on a 2 ml suerose cushion (10'}?} in a 1.3X6.4cm uhracentrifuge tube. The remainder of the tube was filled with 0.02 M phosphate buffer, pH 7.5. After centrifugation at 27,000 rpm (rotor #30, using 6.5 ml adapter, Bcdtman Instruments, Inc., Palo Alto, CA) for 3 h at 5'^'C, the virion pellets were washed gently with 0.02 M phosphate buffer, pH 7.5, and then suspended (ca. 6-8 mg/ml) in the same buffer. Approximately, 80-95% of the virus was recovered by this procedure judging from A^^^ values. Virions were then exposed to the pH 7.5-dissociative medium (0.1 M phosphate buffer pH 7.5, containing 1 mM EDTA, 1 % SDS, and purified bentonite, 50 //g/ml), to release RNA. These samples were then analyzed with density gradient sedimentation (SEHGAL 1973b, Hsu, WHITE andSEHGAL 1977).Sucrose density gradient centrifugations were performed in linear 5-30% gradients (prepared in 0.02 M phosphate buffer, pH 7.0), E.coli tRNA (5 S), rRNA's (17S and 23 S), bacteriophage MS2 (DOS), and tobacco mosaic virus (190S), served as the sedimentation markers, Polyacrylamide gel (5%) electrophoresis for SBMV protein was performed in the neutral-SDS buffer system of MAIZEL (1969) and molecular weight estimations were made according to WRBER, PRINGLE and OSBORN (1972). Negatively stained samples were examined with a Jeol 100 B electron microscope (SEHGAL and Hsu 1977). Ouditerlony double diffusion tests were performed according to SEHGAL and SINHA (1974).

No abstract

A study on the major fisheries was conducted from August 2017 to April 2018 in coastal provinces of the Mekong Delta, Vietnam. Results showed that the gillnets, trawl nets, and stow nets were the main fishing gears, accounted for the highest number of fishing boats and yields. All the fishing gears exploited for the whole year-round. The results also indicated that gillnets fishery is the largest scale (10.99 tons). The most effective fishing activity of gillnets fishy was the highest profit (298 million VND per year) (p <0.05). However, the highest fishing yield (20.42 tons/year) was found in trawler but it had the lowest rate of return (0.45 times) and trash-fish portion accounted the highest ratio (38.4%). Although the stow nets had highest rate of return (1.41 times), but they were lowest yield (7.17 tons/year) and high portion of trash-fish. The high proportion of trash-fish may affect to fisheries resources. For the sustainable development of the fisheries in the Mekong Delta, the development and management of fisheries resources should be promoted, supporting fishermen to access low interest rates to invest in capture production, and training fishermen to use advanced fishing gear to increase their fishing efficiency.