The effects of density and artificial substrate on intensive shrimp Litopenaeus vannamei nursery production

Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m⁻³, low-density with substrate LDS, high-density HD; 3000 PL/m⁻³), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m² of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO₂-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m⁻³) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account.     

Commuting distances to local non‐farm workplaces and out‐migration: The case of Northeast Thailand

The relationship between commuting distances and where people work has been studied for urban contexts in both developed countries and developing countries. However, few studies have examined the situation in rural areas, and none look at commuting distances to non‐farm workplaces in rural areas of developing countries. This paper investigates how commuting distance, and thus accessibility, to local non‐farm work influences non‐farm employment and out‐migration from rural villages in Northeast Thailand. The main issues examined are: (i) the distance that rural residents travel to work in local non‐farm jobs; and (ii) the influence that local non‐farm employment has on the number of outmigrants from rural villages. The study finds: (i) distance between villages and non‐farm work sites impact the number of villagers who are employed in regular wage work; (ii) beyond 20 km villagers are less likely to travel to non‐farm employment using their own means of transportation; and (iii) employment in regular wage work decreases outmigration. The findings from this study contribute to the debates over the drivers of rural out‐migration, rural livelihood changes, and agrarian changes that are taking place in Southeast Asia.     

Assessing the efficacy and impact of management of an invasive species in a protected area: Poa annua on sub‐Antarctic Macquarie Island

Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub‐Antarctic temperatures and their off‐target impacts may increase eradication success. With interest in controlling non‐native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub‐Antarctic biotype) in sub‐Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub‐Antarctic Macquarie Island through field‐based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub‐Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one‐off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow‐up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site‐specific testing of control methods and understanding off‐target impacts of control when managing alien plant species in protected areas.     

基于GEE的东南亚主产区橡胶林分布遥感提取

为遥感监测全球橡胶主产区橡胶的长势,选取橡胶产量最大的泰国、马来西亚、印度尼西亚三国,开展基于Google Earth Engine（GEE）的橡胶林分布遥感提取研究。通过目视解译选择典型样本区,根据Landsat 7多波段光谱特征、MODIS NDVI反映的植被物候特征建立分类回归树CART分类模型提取橡胶林分布。精度评价显示模型总体分类精度为95.8%,Kappa系数为0.94,生产者精度达到94.8%,用户精度为88.2%,达到较高水平。模型提取结果显示：橡胶林在泰国中部、南部半岛,马来半岛的东部和南部地区,苏门答腊岛分布较为集中,而泰国北部、加里曼丹岛及其他岛屿橡胶林相对稀疏。     

The effects of protein kinase A catalytic subunit on sperm motility regulation in Pacific abalone Haliotis discus hannai

Protein kinase A plays a central role in the regulation of sperm motility from echinoderms to mammals, but the information about its regulatory role in molluscs is very limited. In this study, a protein kinase A catalytic subunit (designated as HdPKA‐C) was identified from Pacific abalone Haliotis discus hannai. The open reading frame of HdPKA‐C was of 1,077 bp, encoding a peptide of 358 amino acids with a typical protein kinase domain. HdPKA‐C shared 82%–87% sequence similarities with other PKA‐Cs, and it was clustered first with gastropod PKA‐Cs in the phylogenetic tree. The mRNA of HdPKA‐C was constitutively expressed in examined tissues, with the highest level detected in hepatopancreas. The phosphorylated form of HdPKA‐C (p‐HdPKA‐C) was localized at the acrosome, connecting piece and flagellum of spermatozoa with variable intensity. Its phosphorylated substrates were also detected in these regions with much lower intensity at the connecting piece. The inhibition of HdPKA‐C activity with H‐89 led to a significant reduction in the percentage of motile sperm and sperm velocities. p‐HdPKA‐C was detected by Western blot in strip‐spawned sperm, naturally spawned sperm and H‐89‐treated sperm with almost the same intensity. The intensity of p‐HdPKA‐C substrates in naturally spawned sperm was higher than that in strip‐spawned sperm, and it was roughly the same as that in H‐89‐treated sperm except for two bands at 50 and 60 kDa. These results collectively indicated that HdPKA‐C played an important role in the regulation of abalone sperm motility by altering its substrates phosphorylation.     

Time‐varying relationships between ocean conditions and sockeye salmon productivity

Environmental change is occurring at unprecedented rates in many marine ecosystems. Yet, environmental effects on fish populations are commonly assumed to be constant across time. In this study, I tested whether relationships between ocean conditions and productivity of North American sockeye salmon (Oncorhynchus nerka) stocks have changed over the past six decades. Specifically, I evaluated the evidence for non‐stationary relationships between three widely used ocean indices and productivity of 45 sockeye salmon stocks using hierarchical Bayesian models. The ocean indices investigated were the Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO), and sea surface temperature (SST). I found partial support for time‐varying salmon–ocean relationships. Non‐stationary relationships were strongest for the NPGO and weaker for the SST and PDO indices. Productivity–NPGO correlations tended to shift gradually over time with opposite trends for stocks in British Columbia (B.C.) and western Alaska; for B.C. stocks, the NPGO correlations shifted from significantly negative prior to 1980 to significantly positive after 1990, whereas for western Alaska stocks, the correlations shifted from positive to negative. Productivity–SST correlations showed declining trends for B.C. and Gulf of Alaska stocks, that is, correlations became more negative (B.C.) or less positive (Gulf of Alaska) over time. For the PDO, correlations weakened during the 1980s for western Alaska and B.C. stocks. Overall, these results provide evidence for time‐varying relationships between salmon productivity and environmental conditions over six decades, highlighting the need to recognize that historical responses of salmon populations to environmental change may not be indicative of future responses.     

What the past tells us about the future of Pacific salmon research

The Larkin lectures are held every two years at the University of British Columbia in recognition of Dr. Peter Larkin's contributions to fisheries science. The lecture I presented in November 2015 coincided with an announcement that the Institute of Fisheries that Peter Larkin founded in the 1960s would be restructured as the “Institute for Oceans and Fisheries” with an emphasis on fisheries and oceans issues important to British Columbia as well as the rest of the world. I decided to look back at research issues that Peter Larkin thought would be important for Pacific salmon (Oncorhynchus spp.) in the future and see what has happened as a way of identifying the complexity that the Institute for Oceans and Fisheries in particular and the science community in general will face. I chose five themes from Peter Larkin's talks: 1 understanding marine survival, 2 ocean carrying capacity, 3 aquaculture, 4 climate, Pacific salmon and climate change and 5 informing the public, and then added my opinion about research priorities for the future. Peter Larkin recognized the future relevance of these examples, but he probably could not have imagined how these and related issues will challenge his renamed institute and the rest of the research community over the next 50 years.     

Fluorescence of Extracts from Argentine Hake (Merluccius hubbsi) Muscle and Its Correlation with Quality Indices During Chilled Storage

Argentine hake (Merluccius hubbsi) was stored chilled for 8 days. The evolution of fluorescence of the aqueous and organic extracts of muscle during storage at 4°C was studied and correlated with common damage indices; pH, total volatile basic nitrogen, free fatty acids, and the fluorescence intensity of the aqueous phase showed a good correlation with storage time. The excitation-emission matrices of the aqueous extracts were also obtained. A fluorescence landscape that could be attributed to tryptophan decreased with storage time, meanwhile a peak (around 340 and 400 nm for excitation and emission wavelengths, respectively) is developed during chilled storage.     

Diazotroph community structure and abundance in wheat–fallow and wheat–pea crop rotations

Biological input of nitrogen (N) from the atmosphere by free-living diazotrophs can help alleviate fertilizer use in agricultural systems. In this study, we investigated the effect of N fertilizer and winter pea (Pisum sativum L.) crop on the community structure and abundance of free-living diazotrophs in a two year study of dryland winter wheat (Triticum aestivum L.) no-till production system in Eastern Oregon, USA. Based on quantification of the nifH gene, diazotroph abundance was strongly influenced by plant species and the crop year in which the soil samples were collected. A greater amount of nifH copies was recovered in 2012 compared to 2011 either as copies per gram soil or normalized to the abundance of bacterial 16S rRNA genes. The quantity of genes was greater under pea than wheat in 2012 although no difference was observed in the preceding year. The nifH gene abundance was positively correlated to ammonium concentration in 2011 and bacterial abundance in 2012. Nitrogen application did not influence diazotroph abundance in the top 0–5 cm; however the abundance was reduced by application at the lower 5–10 cm depth under wheat crop. The diazotroph community structure appeared to be influenced more by N fertilization rather than plant species with the exception of wheat in 2012. Changes in the community structure over the two years were greater for fertilized than unfertilized soil. Collectively, these data suggest that year-to-year variability had a greater influence on diazotroph communities rather than specific parameters of plant species, fertilization, total N, total organic C, or soil pH. Multi-year studies are necessary to define the specific drivers of diazotroph abundance, community structure and function.     

Effect of disinfection with peracetic acid on the microbial community of a seawater aquaculture recirculation system for Pacific white shrimp (Litopenaeus vannamei)

When tropical shrimps are kept in recirculating aquaculture systems (RAS), one of the limiting factors is the maintenance of a sufficient water quality, and therefore, often disinfectants like peracetic acid (PAA) are added to the water either as prophylactic or treatment measure. In this study, PAA in concentrations of 0.1 mg/L, 1 mg/L and 10 mg/L was applied continuously for 56 days to small-scale seawater RAS stocked with Litopenaeus vannamei. Treatment with 0.1 mg/L did not result in a reduction in the total bacterial amount and therefore was not effective. A concentration of 10 mg/L led to significant changes in the chemical water parameters already after 2 days and was therefore not recommendable. A concentration of 1 mg/L led to increased levels of ammonia and nitrite within 2 days and to a significant increase in the bacterial amount in the water, most probably due to an enhanced growth of heterotrophic bacteria. The microflora showed significant fluctuations, and there were indications that the welfare of the shrimps was affected. Using 1 mg PAA/L for prophylactic use is therefore also not recommendable but might be an alternative option for short-term treatment in cases of disease outbreaks.