Experimental assessment of the utility of visible implant elastomer tags in a stock improvement programme for giant freshwater prawn (Macrobrachium rosenbergii) in Vietnam

An important requirement of many breeding programmes for aquaculture species is the ability to identify organisms individually or at least by family. While a variety of external and internal tagging methods have been developed that can provide efficient identifications systems, most have specific drawbacks. The present study assessed the efficiency of an internal tagging method that can be applied to family selection programmes in crustacean species. Experiments were conducted to test the efficacy of applying visible implant elastomer (VIE) tags to juvenile giant freshwater prawn (GFP). The first experiment assessed performance of VIE tags in juvenile GFP of different size classes and stability of tags placed in different positions in the abdomen with different numbers of tags implanted. The second experiment applied VIE tags in a long term, large scale, field‐based farming experiment. The third experiment tested the reliability of the system. Results showed that juvenile GFP at 2 g were of suitable size for VIE tags with no negative effects evidence on growth and survival. Tag retention rates were above 97.8% in all experiments and tag readability rates were 100% with a correct assignment rate of 95% through to mature animal size of up to 170 g.     

Identifying resource competition in maize-based soil conservation systems using 13C and 15N isotopic discrimination

Soil conservation measures such as establishing grass barriers or cover crops effectively control erosion but also provoke competition, which reduces yields of companion crops. We used ¹³C and ¹⁵N natural abundance profiles to identify the causes of competition of soil conservation measures on a field with 59% slope in Northwest Vietnam three years after establishment. Treatments were maize under farmer’s practice (T1, control), maize with Guinea grass barriers (T2), maize under minimum tillage (MT) with Pinto peanuts as cover crop (T3), and maize under MT and relay cropped with Adzuki beans (T4). A pretest using data from zero-N plots revealed that abundance of water and limited nitrogen availability induced low grain N concentrations, enriched leaf δ¹³C, and reduced maize grain yield. Similar low N leaf concentrations and elevated δ¹³C values were observed in maize growing close to frequently pruned grass barriers under positive water balance conditions, indicating that yield decline in these rows can be attributed mainly to N competition. Enriched δ¹⁵N values of maize from rows next to barriers indicated reliance on soil N rather than on ¹⁵N-depleted fertiliser N. Vigorous cover crop growth under MT resulted in maize yield decline due to N competition while relay-cropped legumes did not trigger inter-species competition having a similar maize yield, leaf N concentration, δ¹³C, and δ¹⁵N as the control.     

A Natural Forest of Commercial Timber Species: Logging or Not Logging

Most tropical forests outside protected areas have been or will be selectively logged because the timber industry is a main income-generating resource for many developing countries. Therefore, understanding the composition of commercial timber species and logging types is key for sustainable forest management in countries like Vietnam as they move toward fulfilling Reducing Emissions from Deforestation and Forest Degradation (REDD+) agreements. Seven 1-ha plots were surveyed in the Central Highland of Vietnam, and 18 commercial tree species from these plots, whose timber is widely used by local people for housing and furniture making and timber is easily sold at local markets for high prices, were analyzed. In total, 151 tree species with a diameter at breast height (DBH) of ≥?10 cm were recorded. The 18 commercially valuable species assessed in this study accounted for 33.2% of all stems (total of 524 stems ha^?1 for all species), 47.1% of basal area (total of 34.35 m² ha^?1 for all species), and 50.8% of aboveground biomass/AGB (total of 262.68 Mg ha^?1 for all species). Practicing diameter-limit harvesting of all commercially valuable species with DBH of ≥?40 cm, which is widely performed in Vietnam, will reduce the number of stems by 7%, basal area by 31.6%, and AGB by 38.2%. Because such harvesting practices cause severe ecological impacts on the remaining forest, logged forests may require >?40 years to recover the structure status of a pre-logged forest. In addition, the recovery of the 18 commercially valuable species may require a much longer time because they comprised 33.2% of stems. Permission for logging natural forests should be given in Vietnam to sustain lives of local communities, where logging has been prohibited. However, alternative harvesting systems, such as reduced-impact logging systems, should be considered. The systems selected must simultaneously generate economic returns for local people and respect the REDD+ agreements with regard to protecting biodiversity and reducing carbon emissions.     

Genotypic variations in the plasticity of nodal root penetration through the hardpan during soil moisture fluctuations among four rice varieties

Rainfed lowland rice fields are characterized by soil moisture fluctuations (SMF) and the presence of hardpan that impedes deep rooting and thus limits water extraction from deep soil layer during the periods of drought. In this study, we used rootboxes with three layers; shallow layer, artificial hardpan, and deep and wet layer below the hardpan, to evaluate differences in the plasticity of nodal roots elongation through the hardpan and promote root branching below the hardpan in response to SMF among four rice varieties; Sasanishiki, Habataki, Nipponbare, and Kasalath. Experiments were conducted during the summer and autumn seasons. Plasticity was computed as the difference in root traits within each variety between the SMF and continuously well-watered treatments. In both experiments, Habataki consistently tended to exhibit higher root plasticity than the other three varieties by increasing number of nodal roots that penetrated the hardpan during rewatering period in SMF, when the soil moisture increased and penetration resistance decreased. This root plasticity then contributed to greater water use at the deeper soil during the subsequent drought period and overall shoot dry matter production. Habataki had significantly higher δ¹³C value in roots at deep layer than roots at the shallow and hardpan layers under SMF, which may indicate that these were relatively newly grown roots as a consequence of root plasticity. This study also indicates that CSSLs derived from Sasanishiki and Habataki varieties may be suitable for the analysis of QTLs associated with root plasticity expression in rainfed lowland with hardpan and experiencing SMF.     

Warming Increased Nitrogen Availability and Tree Growth During the Last Five Decades as Revealed by Annual Ring Data of Pinus merkusii in Central Vietnam

The effects of climate change including warming on nitrogen (N) availability and growth of Pinus merkusii in central Vietnam were investigated using the relationship between climate variables (rainfall and temperature) and tree-ring parameters (ring width, density, basal area increment, and N concentration) for the last five decades. Rainfall was not correlated with any tree-ring parameters, indicating that water availability did not limit tree growth in the study site probably due to sufficient rainfall. Temperature was positively correlated with ring N concentration, basal area increment, and ring density, probably reflecting the positive effects of warming on soil N mineralization, net photosynthesis, and cell wall thickness, respectively. Therefore, this study suggested that global warming during the last five decades increased N availability and the increased N further helped warming-induced increases in the growth of P. merkusii in central Vietnam.     

Incorporation of rice straw mitigates CH4 and N2O emissions in water saving paddy fields of Central Vietnam

This study evaluated the effects of rice straw and water regimes on CH₄ and N₂O emissions from paddy fields for two rice growing seasons (summer 2014 and spring 2015). Water regimes included alternating wet–dry irrigation (AWD) maintained at three levels (–5 cm, – 10 cm and –15 cm) in comparison to continuous flooding irrigation (CF). Rice straw (5 t ha^–1) was incorporated into the top soil (0 – 15 cm), distributed and burned in situ. Results showed that using burned in situ rice straw was found to reduce seasonal cumulative CH₄ emission (24–34% in summer; 18–28% in spring), N₂O emission (21–32% in summer; 22–29% in spring) and lower rice yield (8–9%) than rice straw incorporation into top soil. AWD methods reduced the amount of CH₄ production (22.6–41.5%) and increased N₂O emission (25–26%) without any decrease in rice yield. Rice straw incorporation into the top soil with AWD had higher water productivity (23–37%) than rice straw when burned in situ with CF. The results conclude that AWD and rice straw management can be employed as mitigation strategy for CH₄ and N₂O emissions from paddy fields in Central Vietnam.     

Efficiency of amino acid utilization in the growing pig at suboptimal levels of intake: lysine, threonine, sulphur amino acids and tryptophan

A series of N balance experiments using growing pigs was conducted to study the efficiency of utilization of lysine, threonine, sulphur amino acids and tryptophan and to estimate their maintenance requirements. Purified diets based on casein and crystalline amino acids as the sole source of N contained graded levels of each amino acid, corresponding to expected protein accretion rate of 0, 33, 66, 99 and 132 g/day, respectively. N retention increased linearly (p < 0.01) as the dietary concentration of the limiting amino acid increased. Based on linear regression equations relating amino acid deposition in body protein to amino acid intake, marginal efficiencies of ileal digestible amino acid utilization were calculated to be lysine 0.91, threonine 0.83, sulphur amino acids 0.85 and tryptophan 0.66. Extrapolating the regression equations to zero N retention, the daily requirements of amino acids for N equilibrium were estimated to be (mg/kg(0.75)) lysine 39, threonine 49, sulphur amino acids 46 and tryptophan 16.     

Susceptibility of freshwater rearing Asian seabass (Lates calcarifer) to pathogenic Streptococcus iniae

Asian seabass (Lates calcarifer) has been recognized as an economically important aquaculture species which can be adapted to and cultivated in wide range of salinities. The number of freshwater intensive seabass farms in Thailand is increasing annually. Here, we first describe the susceptibility of Asian seabass, which were cultured in freshwater, to Streptococcus inae (SI) and their pathological changes. Three isolates of putative SI were identified using a combination of standard biochemical assays and species‐specific PCR prior subjected to in vivo challenge. Accumulated mortalities of the fish which received 10⁷ CFU fish^?1 of either SI1J, SI SGSA or SI2J were 90%, 90% and 100% at 7 days‐post infection (dpi), respectively, and mortalities increased sharply between 3 and 5 dpi. Clinical signs such as erratic swimming and opaque eyes were identified from a few infected fish, while most died rapidly without any abnormal signs. Histopathological manifestations were observed in the multiple organs (kidney, liver and brain). Haemorrhage, hyperhemia, cellular degeneration and inflammatory cells infiltration were commonly found within the internal organs. Notably, the formation of numerous encyst‐like lesion aggregated by eosinophilic cells, resembling macrophages, were typically found in the brain of the infected fish. Summarily, this study first revealed that freshwater reared Asian seabass is highly susceptible to SI infection and haemorrhagic septicaemia was a major pathological change that could be found in the infected fish.     

Salinity and temperature effects on productivity of a tropical calanoid copepod Pseudodiaptomus incisus

Pseudodiaptomus species are major live feeds for the early stages of economically important marine fish in hatcheries in the South China Sea. However, we know little about the combined effects of multiple environmental parameters such as salinity and temperature on copepod productivity. To address the issue, we cultured a tropical coastal copepod Pseudodiaptomus incisus in one of 24 combinations of 8 salinities (5, 10, 15, 20, 25, 30, 35 and 40 ppt) and 3 temperatures (26, 30 and 34°C). We determined development, biomass of all stages, fecundity, percentage of females with hatched eggs and 30 hr nauplii production. Overall, the biomass, fecundity and nauplii production of P. incisus were highest at the salinity of 15–20 ppt, especially at 26°C. P. incisus showed a lower performance at both lower and higher salinities. Elevated temperatures resulted in faster development, but lower biomass, fecundity and nauplii production. Especially, nauplii production was reduced by 74% at 35–40 ppt and 34°C compared to at 15–20 ppt and 26°C. Our study provides essential information for optimizing the biomass culture of P. incisus.