Improving Sustainability of Striped Catfish (Pangasianodon Hypophthalmus) Farming in the Mekong Delta, Vietnam, Through Recirculation Technology
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Improving sustainability of striped catfish (Pangasianodon hypophthalmus) farming in the Mekong Delta, Vietnam, through recirculation technology Nguyen Nhut Thesis committee Promotor Prof.Dr J. A.J.Verreth Professor of Aquaculture and Fisheries Wageningen University Co-promotor Dr M. C.J. Verdegem Associate professor, Aquaculture and Fisheries Group Wageningen University Other members Prof. Dr. M.K. van Ittersum, Wageningen University Prof. Dr. H.H.M. Rijnaarts, Wageningen University Dr A.A. van Dam, UNESCO-IHE, Delft Prof. Dr D.C Little, University of Stirling, United Kingdom This research was conducted under the auspices of the Graduate School of Wageningen Institute of Animal Sciences (WIAS). Improving sustainability of striped catfish (Pangasianodon hypophthalmus) farming in the Mekong Delta, Vietnam through recirculation technology Nguyen Nhut Thesis submitted in fulfillment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus, Prof.Dr A.P.J Mol, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Monday 19 December 2016 at 11 a.m. in the Aula. Nguyen Nhut Improving sustainability of striped catfish (Pangasianodon hypophthalmus) farming in the Mekong Delta, Vietnam through recirculation technology, 180 pages. PhD thesis, Wageningen University, Wageningen, NL (2016) With references, with summary in English. ISBN: 978-94-6257-919-4 DOI : http://dx.doi.org/10.18174/394644 Abstract The aim of this thesis was to document improvements in sustainability indicators of striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878) production through the application of recirculation and waste treatment techniques. To be able to document improvements in sustainability, in each system studied the same set of twenty sustainability indicators were measured. Indicators related to the use of fingerlings, water, diesel oil, electricity, labor, chemicals and antibiotics. Also, indicators related to nutrient utilization efficiencies and waste discharge were monitored. In addition, a sampling scheme, allowing to calculate organic matter, nitrogen, phosphorous and chemical oxygen demand mass balances covering a full production cycle and applicable in different production systems, was developed. Overall, from a sustainability point of view, striped catfish culture in ponds compared well to other important aquaculture species. Although favorable, it was concluded that water, chemicals and antibiotics use, survival, and the amounts of waste discharged could be further reduced through recirculation and treatment of solid wastes. The realized improvements through RAS technology and waste treatment technology were quantified in lab or pilot scale experiments. Large improvements were realized for water, antibiotic and chemical use, survival, waste discharge and color grade of striped catfish fillets at harvest. In addition, in RAS, utilization efficiencies of nutrients supplied through feeding were improved. Solid wastes removed from ponds or RAS could be partially re-used by making compost or producing methane for generating electricity. Another approach tested was the integration of a denitrification reactor in the recirculation system, which allowed to decompose solid waste and reduce nitrogen discharge. Denitrification in RAS did not affect fish growth, nutrient retention efficiencies and the quality of the fish fillets produced, and thus also improved sustainability of striped catfish farming. In conclusion, application of recirculation and waste treatment techniques tested in this thesis improved the sustainability for striped catfish culture. The challenge remains to scale up RAS and waste treatment technology for striped catfish to the production volumes handled in outdoor ponds without raising production costs. Contents Chapter 1. General introduction 7 Chapter 2. Nutrient mass balance and water use in striped catfish 19 (Pangasianodon hypophthalmus, Sauvage, 1878) pond culture: down-stream versus up-stream Chapter 3. Nutrient mass balances, water quality and water use of striped catfish 51 (Pangasianodon hypophthalmus, Sauvage, 1878) in flow-through and recirculation systems Chapter 4. Biogas production and compost composition of sludge from striped 85 catfish (Pangasianodon hypophthalmus, Sauvage, 1878) ponds and recirculating systems Chapter 5. Effect of an upflow-sludge-blanket denitrification reactor on 113 environmental sustainability of striped catfish production (Pangasianodon hypophthalmus, Sauvage, 1878) in recirculating aquaculture systems Chapter 6. General discussion 143 References 155 Appendices 168 Summary 169 Acknowledgements 173 Curriculum vitae 175 Training and supervision plan 179 Colophon 180 CHAPTER 1 General introduction 7 Chapter 1 1.1. Striped catfish culture Striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878) is a facultative air breather (Lefevre et al., 2011c), endemic to the Mekong basin in Cambodia, Laos, Thailand and Vietnam and the Ayeyawady basin of Myanmar. It has been introduced to many other Asian countries, including India, China, Bangladesh, Indonesia and the Philippines (FAO, 2010). Today, Vietnam is the largest producer of striped catfish in the world, producing 1.1 million tonne per year in 5,000 ha of ponds. The product is exported to more than 130 countries (MARD, 2014a). Initially, different culture system models were used, including poly and mono culture ponds, cages and pens (Figure 1.1). 2000 Total Cage 1800 Pen 1600 Pond 1400 1200 1000 800 600 400 Striped catfish production (x 1000 MT) 1000 (x productionStriped catfish 200 0 1997 1999 2001 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 1.1:Striped catfish production by production system in Vietnam (MARD, 2014a) Today, striped catfish is raised in none aerated 2 to 6 m deep ponds, realizing productions of 70 to 850 metric tonnes per ha per crop (Phan et al., 2009). Almost all ponds are located along tributaries of the Mekong river which is convenient to discharge nutrients to the river 8 General introduction and to transport feed, fingerling and market size fish to or from the farm. The amount of water used per kg fish produced ranges between 2.5 and 9.1 m3 (Anh et al., 2010; Bosma et al., 2009; Phan et al., 2009). Commercial floating 22 – 30% protein pellets are fed, realizing a feed conversion ratio ranging between 1.5 and 1.8 (Bosma et al., 2009; Phan et al., 2009). Per kg striped catfish produced, waste containing 46 g nitrogen (N) and 14 g phosphorous (P) is produced (De Silva et al., 2010). About 70% of striped catfish farmers discharge untreated effluents to the river. The remaining 30% of farmers discharge to rice fields or gardens (Phan et al., 2009), where part of the nutrients are reused. Discharging effluents pollute surface waters and increases the risk of horizontal disease transmission (Nguyen et al., 2007). Survival in striped catfish ponds is less than 70% mainly due to disease. More than 15 diseases/syndromes are commonly occurring in striped catfish farming (Phan et al., 2009). Diseases are treated with different antibiotics and chemicals (Bosma et al., 2009; Rico et al., 2013). However, consumers do not accept residues of antibiotics and chemicals in fish products leading to national and international laws and regulations that limit the number and amounts of chemicals and antibiotics farmers can use. When applying chemicals or antibiotics farmers are advised to ban application during the last 2 months before harvesting (BMP, 2009; MARD, 2011) . Consumers prefer white fillets, but fillets can have grades of pink or yellow colour (Sang et al., 2009). Only white fillets are of export quality and fetch a higher price (Khoi, 2011). The fillet colour of striped catfish produced in deep ponds in the Mekong Delta is predominantly white. The high depth and water turnover rate of the pond farming system in the Mekong delta might contribute to more white fillets (Phu et al., 2014). Farmers will be willing to switch to less polluting farming systems, provided the colour grade of the fillet is maintained. 1.2. Aquaculture sustainability indicators Sustainability includes environmental, economic and social dimensions (Verreth and Oberdieck, 2009), and to monitor and compare sustainability performance indicators are required that are measurable and easy to apply at farm level. Basic indicators used to assess sustainability of aquaculture production systems are listed in Table 1.1 (Boyd et al., 2007; Verreth and Oberdieck, 2009). 9 Chapter 1 Comparisons of sustainability indicators across species, farming systems and countries or regions is important to develop standards for sustainable aquaculture. For example, trout production in Europe consumes more water in raceways than in recirculating aquaculture systems (RAS) (d’Orbcastel et al., 2009b), water use per kg fish produced being a sustainability indicator. Combining the different sustainability indicators, fish production in RAS showed better sustainability than production in raceways, cages or ponds (Eding et al., 2009). However, RAS technology has not been widely adopted due to high costs and the level of knowledge required (Ngoc et al., 2016a). Today, numerous fish farmers are willing to voluntarily adopt best management practices to reduce negative impacts from aquaculture on the environment and to better satisfy consumer demands for healthy and sustainable produced fish (Boyd et al., 2007; Ngoc et al., 2016a). Table 1. 1: Some basic sustainability