As the nursery fever reigns, in Vietnam, the three-phase BIOSIPEC system comprising highdensity nursery and pre grow- out phases isolates each phase with its own unique biosecurity protocol and reduces risk of crop failures.
By Marcell Boaventura, Georges Hetzel, Cuong Huynh Tran, Sjoerd Bakker and Marc Campet
Worldwide, the effects of disease outbreaks remain the most serious restraint for the growth of the shrimp industry. Disease-led crop failures have been prompting producers to investigate new sustainable technologies for increased consistency of output. The implementation of modular intensive farming systems is challenging, but highly rewarding in terms of infrastructure utilisation, shrimp growth and survival as well as feeding management along with higher and more consistent output. The nursery phase is an intermediate step between the hatchery and grow-out stages and is responsible for substantial improvements in performance and the efficient use of resources. This article describes the main principles and advantages of the nursery system and displays the achievement of consistent results of BIOSIPEC, a three-phase modular system, which combines applied science and technology with the needs and realities of commercial production.
Incoming water is the main path for the introduction of pathogens in the rearing system. Operating systems under strict biosecurity control require the full disinfection of incoming water. Effective water disinfection systems are expensive, hence reducing water requirements with closed systems and semi-biofloc and biofloc, help to maintain the efficacy of filtration at a low operation cost for successful and sustainable intensification of production. In the past, intensive systems required high water exchange to maintain the water quality.
Figure 1 below shows the development of farming areas in India and reminds us that pristine water is no longer available in most farming areas given the growth of aquaculture in the last decade. A number of publications document the reduction in water requirements and discharge of nursery systems (Cohen et al., 2005; Khanjani et al., 2016) and this is a crucial factor for the sustainable development of the shrimp industry.
In intensive semi-biofloc nursery systems, strict control must be given to the following: biosecurity, post larvae quality, stocking density, feed quality and feeding ration, dissolved oxygen, suspended solids, free carbon dioxide, pH, alkalinity and light penetration. The biofloc system passes through a maturation process. In the early days while the system is still immature, heterotrophic bacteria are responsible for the recycling of all nutrients. At this stage, continuous addition of a carbon source is required. In the secondary stage, chemo-autotrophic bacteria communities are also established; the feed along with alkalinity management becomes the main sources of carbon.
In the early days, excess microalgae can delay the achievement of the optimum balance of microorganisms mainly to the fluctuations of pH and dissolved oxygen levels. These systems work well at low levels of microalgae. Shading the culture or maintaining it indoors represents a major advantage to achieve the consistent equilibrium of the microbiota communities.
Post larvae quality is fundamental to achieving good results. While specific pathogen tolerant (SPT) and specific pathogen resistant (SPR) animals are desirable, working with specific pathogen free (SPF) stock is usually sufficient, given that the system aims for the complete isolation of the animals from the external environment, throughout most of the cycle. Nevertheless, continuous application of commercial probiotics and health surveillance are required for the early detection of potential breaches in the biosecurity system. The continuous maintenance of an integrated farming system, which focuses on the optimum operation practices as demonstrated in Figure 2 is also important. Not to forget, record keeping and traceability are of the highest importance. Accurate information of each supplies including detailed information on post larvae must be available and diligently recorded.
Semi-biofloc as a tool to reduce water exchange
The effluents of intensive nursery systems are rich in nutrients such as nitrogen and phosphorus, along with suspended organics and high biochemical oxygen demand (BOD, McIntosh et al., 2001). With adequate management and control of carbonaceous substrate, microorganisms can uptake these metabolites, maintaining the water quality, reducing nutrient release and recycling the waste into nutritious biofloc, which is a natural food for detritivores such as shrimp. In a study comparing efficiency of a biofloc system using low and high protein content, no detrimental effects to water quality could be linked to the use of a high protein diet (Brito, 2018)
In an intensive biofloc system, up to 40% of shrimp biomass can be obtained from the biofloc produced and consumed in the system (Burford et al., 2004; Cardona et al., 2015). The direct benefits are a reduction in feed demand and feed conversion ratio (FCR) along with an increase in efficiency. These days, the availability of post larvae from strong family selection systems is a reality. Fast growth is one the main traits targeted by the global shrimp breeding centres, but only gives a potential of what the shrimp can achieve in terms of growth. To reach that potential, protein along with other nutrient requirements are required in adequate levels. The supply of highly digestible protein with the proper amino acid profile is key in reaching the potential of the new shrimp genetic lineage but also reduce pollution of the rearing water. A recent study conducted at the Institute of Marine Sciences – Labomar, in Brazil, demonstrated a 12% gain in survival, 8% reduction in FCR along with a reduction of size variability by half when using BernAqua’s MeM (a cold microextruded diet), in comparison to a regular crumble, during a 56-day nursery process.
2.5 years of experience on nursery and biosecure intensive shrimp farming
Running since September 2017, BIOSIPEC is the Bio-Secure Intensive Shrimp Production pilot of ADM in Vietnam. The production cycle in this system is divided into three phases: a nursery, a pre grow-out and a grow-out phase. Having the production cycle divided into three phases will allow for five cycles per year, adjustment of energy consumption for each phase and a better control of the environment. (Table 1 and Figure 3)
In this nursery system, there is a 30m3 raceway located in a greenhouse and thus protected from the rain, light and external contamination. The cycle starts with post larvae (PL10) and runs for 4 weeks with a density ranging from 8 to 10 PL/L to reach a survival of over 80% and FCR around 0.95. From the beginning, the animals are fed with formulated feed to avoid any contamination. The PL10 are fed with MeM 200-300 (BernAqua) at 30% of the biomass, before slowly decreasing the feeding rate to finish at 6% to 8% biomass with a specific extruded nursery feed, Vana Nano feed (Ocialis). At the end of 4 weeks, the shrimp reach 300mg on average, which may seem low when compared to the results in lower density cultures, such as at one PL/L, but higher density culture saves space and energy. Water consumption is around 300m3 for the nursery cycle, which represents around 3.6m3/kg of biomass produced. This represents a reduction in cost as well as a minimising risks with introduction of pathogens.
Low water consumption also allows the regulation of the mineral balance of the water. Indeed, during the nursery phase, shrimp can undergo 10 to 15 moulting during which it is crucial to have the perfect mineral balance. In cases of low salinity, successful artificial salinity and mineral balancing have been performed at BIOSIPEC.
A few steps ahead of the development of shrimp nursery
The last few years have seen the concept of nursery spreading across all shrimp production regions such as Vietnam, India and the Philippines. Farmers quickly calculated the advantage of a nursery phase compared to direct stocking. However, the current trend is to run low-density nurseries (1PL-2PL/L), which barely compensates for the investment costs. BIOSIPEC is two steps ahead of this trend and adopts the following features:
- More cycles per year, higher density, with optimisation of the surface and energy consumption,
- Partitioning the usual farming cycle into three phases and isolating each phase, which allows the implementation of a specific biosecurity protocol for each phase and reduce the risk of crop failures.
Having a BIOSIPEC demo-farm has allowed ADM to develop its own expertise in innovative and intensive shrimp production. Currently, the demo-farm serves as a training site for customers and technical teams to be acquainted with products and protocols adapted to the requirements of a high-density nursery.