Vol. 16 No. 9 (2018)

This study was conducted to analyze the economic efficiency of skipjack tuna (Katsuwonus pelamis) value chain capturedin south central regionand to propose solutions for upgrading the chain. Data collected through interviews with 175 actors involved in the skipjack tuna value chain in 2017were used forchain economic analysis. Results showed thatthe profit distributionsper kg and ofthe total volume of raw skipjack tuna(about 83,000 tonnes/year) between the respective chain actorswere63.4 and 74.2% for fishermen, 4.9 and 5.6% for middlemen; and 31.1% and 20.18% for processing enterprises, respectively. However, if calculated on a chain actorbasis, the average profit distribution per fisher wasverylow, as this actorgroup mainly organized themselvesinsmall-scale productionat householdlevel(about 2,000 fishing households),leadingto low production efficiencyand lack or limited capacity to link with other actors in the chain. The solutions to improve the value chain of skipjacktunain the direction of efficiency and sustainabilityinclude: promotingchain linkages to increase the scale of production and improve the quality of raw materials; product diversification and branding; and developing policies to support the development of the chain (credit, insurance, risk sharing).

This study compared the growth and survivalratesofwhite-leg shrimp (L. vannamei) which were reared in freshwater at 0 ppt and in saline brackishwater at 30 ppt. PL34 shrimps were reared at the density of 1 individiual/L (200shrimp/m2) for 21 days. Shrimps of each treatment were reared in three 40 L tanks. Results showed that there was no significant difference in survival and growthratesofthe white-leg shrimpshrimpbetween the two treatments during the whole culture period. The survival rates of shrimp reared at 0 ppt and 30 ppt were 62.5 ± 10.9% and 69.17 ± 7.64%, respectively. The weight gain of shrimp reached113.33± 15.28% for shrimp at 0 ppt and 106,67± 11,55% for those at 30 ppt. The specific growth rate of shrimp at 0 ppt and 30 ppt was 3.78 ± 0.36% and 3.63 ± 0.28%, respectively.In conclusion, white-leg shrimp could be reared in freshwater 0 ppt.

Neobenedenia girellaeand Benedenia seriolaeare the two most common capsalid monogeneans of more than 100 marine fish species distributed worldwide. However, these two parasitic species have similar morphology, making it difficult for farmers to distinguish. Praziquantel is the most common selection for treatment of these two parasites, but outbreaks sometimes occurr after treatment. The aim of this study was to evaluate the efficacy of praziquantel to N. girellaeand B. seriolaeon experimentally infected Amberjack for effective control. In this study, eggs and larval development of N. girellaeand B. seriolaewere examined and they were used to infect the experimental fish, Amberjack (Seriola dumerili). The infected fish were then treated with praziquantel at the same dosage of 100 mg/kg body weight/day for three consecutive days. After treatment, the number of live flukes present on the fish was separated usingfreshwater bath containing Aqui-S (1: 1000). The results showed that B. seriolaepost-treatment reduction was 100%, while only 44.6% of N. girellaewere killed post-treatment. This indicates thatpraziquantel is completely effective in controlling B. seriolae, but less effective for N. girellae. The results of this study suggestthat the outbreak occurringpost treatment is probably caused by N. girellae. It is thus necessary to develop a rapid and simple methodto distinguish between B. seriolaeand N. girellaeprior to treatment to achieve the highest efficacy in disease management.

A study was conducted to investigate the effects of different stocking densities and dietary protein levels on growth, survival rates and feed conversion ratio (FCR) of armorhead catfish (Cranoglanis henrici). Juvenile fish at the size of 16.79 ±0.92 g/fish and 39.91±0.75 g/fish, respectively,were located into two separated trials of three stocking densities(30, 45 và 60 fish/m3) and three diets containing graded levels of dietary protein (30, 35,and 40% CP). Triplicate groups of 8m3indoor circular tanks were used for arearing period of 60 days. Results showed that significant FCR was recorded at the density of 60 fish/m3(2.96) compared to that at the treatments of 45 fish/m3(2.81) and 30 fish/m3(2.68) while no significant difference (P>0.05) in growth was found. The fish weight ranged from 33.04 to 34.55 g/fish and survival rate washigher than 88% after 60 days of culture. The growth rates of fish fed protein levels of 35% (0.52 g/fish/day) and 40% (0.53 g/fish/day)were similar and significantly higher (P<0.05) than that of 30% (0.35 g/fish/day), while the survival rate over94% were recorded in all treatments. Based on the above results, it is recommended that armorhead catfish juvenile can be reared at stocking densities (in composite tanks) of 45-60 fish/m3and feed containing 35-40% crude protein isoptimalfor growth and FCR.

Real surface temperature and vegetationare important factors providing information on soil moisture. Surface temperature may increase quickly when land surface is waterless or plants are not supplied with enough water. In this study, the surface drought situation in Luc Ngan District, BacGiang Province was assessed by quantifying the relationship between real temperature and vegetation coverusing Temperature Vegetation Dryness Index (TVDI) derived from Landsat satellite images. The study producedthree mapsof surface temperature distribution and three maps of surface drought classification of Luc Ngan district on 24 May 1999, 3 May 2010 and 28 May 2017 asthe scientific basis for the assessment of drought situation and solutionsto minimize the damage of drought toagricultural production.

The present study used numerical simulation method by Eta/ Dynaform software as the basis for the analysis and evaluation of metal deformation process. This restrictsand overcomesthe errors that may occur during manufacturing, saving the time of moldingandfabrication details, saving materials,reducingthe price, and improvingthe quanlity of product after stamping. Based onsimulation problem on the deformation process of some typical partsin agricultural machines from sheet metal, optimal technologicalparameters for shapingwere proposed. On this basis, it is possible to apply virtual technology into production of equipment,machines and products in engineeringin general and agricultural engineering in particular.

The objective of the present study was to purify and determine the properties (optimal temperature, heat stability, optimal pH, pH stability, effects of metal ions) of cellulase derived from Bacillussp. M5strain. The crude enzyme produced from the culture of cellulase-producing bacillus M5 strain was collected by centrifugationand precipitated for purification andcharacterization. To investigate the enzyme's characteristics onoptimal temperature, pH as well as heat stability, pH stability and the effect of certain metal ions, the enzyme fluid was treated under different conditions. The enzymewas disolvedin acetate buffer pH 5.50 mM to determine enzyme activity. Results showed that the cellulase from Bacillus M5 strain was active at an optimaltemperature of 65C; optimalpH of 5.5; heat stability at about 50C (activity remains53% after 120 minutes); pH of 6.0 to 6.5.Ca2+and Mg2+metal ions increasedenzyme activity and Zn2+ion decreasedenzyme activity. The enzyme hadthemolecular weight of 45 kDa.