Showing papers by "Johan A.J. Verreth published in 2016"

Probiotic legacy effects on gut microbial assembly in tilapia larvae

Abstract: The exposure of fish to environmental free-living microbes and its effect on early colonization in the gut have been studied in recent years. However, little is known regarding how the host and environment interact to shape gut communities during early life. Here, we tested whether the early microbial exposure of tilapia larvae affects the gut microbiota at later life stages. The experimental period was divided into three stages: axenic, probiotic and active suspension. Axenic tilapia larvae were reared either under conventional conditions (active suspension systems) or exposed to a single strain probiotic (Bacillus subtilis) added to the water. Microbial characterization by Illumina HiSeq sequencing of 16S rRNA gene amplicons showed the presence of B. subtilis in the gut during the seven days of probiotic application. Although B. subtilis was no longer detected in the guts of fish exposed to the probiotic after day 7, gut microbiota of the exposed tilapia larvae remained significantly different from that of the control treatment. Compared with the control, fish gut microbiota under probiotic treatment was less affected by spatial differences resulting from tank replication, suggesting that the early probiotic contact contributed to the subsequent observation of low inter-individual variation.

Economic feasibility of recirculating aquaculture systems in pangasius farming

Abstract: This study aims to analyze the economic feasibility of recirculating aquaculture systems (RAS) in pangasius farming in Vietnam. The study uses a capital budgeting approach and accounts for uncertainty in key parameters. Stochastic simulation is used to simulate the economic performance of medium and large farms operating with a traditional system or RAS. Data are obtained through structured surveys and a workshop in the Mekong River Delta. Results show that for large farms, net present value increases from an average of 589,000 USD/ha to 916,000 USD/ha after implementing RAS. Overall, the probability that RAS is a profitable investment is found to be 99% for both farm sizes. With RAS, the crucial parameters determining profitability are price, yield, costs of fingerling, feed, and initial investment. Findings on the robustness of the economic performance of RAS are useful to support public and private decision making towards increasing the sustainability of pangasius production.

Feed intake, growth and nutrient retention of common sole (Solea solea L.) fed natural prey and an artificial feed

Abstract: This study compares growth, intake and retention efficiencies of nutrients and energy between common sole (Solea solea L.) fed ragworm (Nereis virens, Sars), blue mussel (Mytilus edulis L.) and an artificial (commercial) feed. Food types were fed to common sole (mean initial body weight: 44.9 ± 2.3 g) in excess three times a day over a 54-day-period. The growth rate in common sole fed the natural prey (8.5 g kg-0.8 d-1) was significantly higher compared to the growth rate in fish fed the artificial feed (5.1 g kg-0.8 d-1). Nutrient and energy intake was significantly lower in common sole fed the artificial feed than in fish fed natural prey. The only exception was fat intake which was higher in common sole fed the artificial feed in contrast to fish fed the natural prey. Nutrient and energy retention efficiencies were significantly lower in common sole fed the artificial feed than in fish fed the natural prey. In conclusion, the low growth in common sole fed the artificial feed was related to lower nutrient and energy intake as well as lower nutrient and energy retention efficiencies. It is suggested that reduced intake of the artificial feed might be related to the high dietary fat content of the artificial feed.

A Decision Tree Analysis to Support Potential Climate Change Adaptations of Striped Catfish (Pangasianodon hypophthalmus Sauvage) Farming in the Mekong Delta, Vietnam

Abstract: This study uses the decision tree framework to analyse possible climate change impact adaptation options for pangasius (Pangasianodon hypopthalmus Sauvage) farming in the Mekong Delta. Here we present the risks for impacts and the farmers' autonomous and planned public adaptation by using primary and secondary data. The latter studies showed that a proportion of the pangasius farms located in the coastal provinces will be affected by salinity intrusion in the dry season. Options to adapt to this are: modify pangasius farming practice, stock other species or stock saline-tolerant pangasius. With research and extension support, farmers can further improve their already adapted practice to deal with salinity or use water recirculation systems for prolonged nursery rearing. A breeding program for saline­ tolerant striped catfish requires a medium-to long­ term investment (0.4 % of the production cost) from government and/ or private company. Pangasius farms in up- and mid-stream regions and in coastal areas, which are not located within upgraded government dyke-protected areas, will be affected by flooding at the end of each rainy season. This implies an increased cost for dykes to about 0.34% and 0.25% of the total variable costs for one harvest per ha in the up- and mid-stream regions, and in the downstream region, respectively.