Thursday, June 23, 2016

Shrimp biofloc technology – efficient and biosecure operation system

Author: Nyan Taw PhD
Published in November/December 2015 AQUA Culture Asia Pacific Magazine

For sustainable and efficient intensive shrimp farming, consider these three major factors: farm biosecurity, energy efficiency and bioflc technology

Shrimp farm biosecurity

Farm biosecurity begins with the design and construction of the farm. Historically, the development of shrimp farms started with ponds utilising simple water flw-through systems in the 1980s. Later, reservoirs to treat incoming water before use were established. The main purpose of reservoirs was to have consistently good water quality, mainly with regard to salinity, temperature and pH as well as the presence of the correct species and amount of phytoplankton in the reservoir and the culture ponds. This will reduce stress to shrimp as well as minimise the presence of Vibrio from the incoming water. In the early 2000s, prior to the introduction of biofloc systems in Asian shrimp farming, green water was normally used in shrimp ponds or in hatcheries. Before stocking post larvae, there should be a certain
level of phytoplankton developed in pond water

Today, modular systems using reservoirs to treat incoming water and minimising water exchange in the culture ponds provide the biosecurity required to control emerging viral problems (Taw, et al 2002; Taw, 2005; Taw, et al 2007). In fact, the shrimp biofloc system was adapted from systems which utilise low water exchanges. These systems develop phytoplankton fist and later a cross over to bioflc colonies. The major differences are with the use of molasses or grain pellets as the carbon source to increase the ratio of carbon: nitrogen (C:N), use of aerators throughout the culture duration and the use of 10% more energy input is to provide the dissolved oxygen required by heterotrophic bacteria within a biofloc colony (Taw, et. al 2004; Taw, 2005; Taw, 2012: Taw 2013; Taw, 2014 and 2015).

As biofloc technology uses zero water exchange, it reduces risks of diseases entering the farm facility through the incoming water. However, in this case, reservoirs, culture ponds, water supply, discharge canals and gates need to have the same level of biosecurity. The practice is to develop flocs in culture ponds. Water from reservoirs is used to compensate for pond water loss from evaporation and to replace water lost through siphoning while cleaning ponds. With a biosecure farm design and construction, a biosecure operating system needs to be in place (Taw et al, 2009; Taw 2010, 2012). Recently, shrimp farms especially in Malaysia are required to have effiient waste water treatment systems before discharging water into the environment. Considering the major challenges faced by farmers today, biofloc technology appears to be the way to go.

Energy effiiency
In intensive shrimp culture systems energy is a major cost factorAn extra one hp used in a pond costs more not only in terms of equipment but also with costs for maintenance, energy and manpower. In Indonesia, Thailand and Malaysia, it is common for one hp of aeration to produce an average of 500 kg of shrimp in conventional intensive systems. However, in biofloc systems, the effiiency can rise to as high as 680 kg/hp (Kopot and Taw, 2004; Taw et al 2012, 2013).

At the Belize Aquaculture Ltd farm, McIntosh (2000) reported 450-550 kg shrimp/hp of paddlewheel aeration in culture ponds using the biofloc system. With partial harvesting, the effiiency can be at a maximum of 1,124 kg/hp (Taw, et al. 2008, Figure 1). McNeil (2004) reported that pressure differential piping (PDP) which produces slower-rising bubbles could achieve 700 kg/hp shrimp whereas paddle wheel aerators could produce between 400-450 kg/hp. A combination of paddle wheel aerators and PDP has better effiiency (Taw, et al. 2008). Measuring shrimp production is much more accurate using energy input than by pond area (per hectare basis) as pond depths may range from 1.2 to >2.0 m.

Figure 1. Energy effiiency of shrimp culture in algae and biofloc systems

In shrimp bioflc technology system, the carrying capacity of the pond has to be determined for effiient and optimum production. This will depend on the size, depth and type of pond and availability of energy input. Another important factor will be the type and effiiency of aerators used. Basically, the farmers need to know the equipment being used. Aeration systems are not meant to increase but rather to maintain the dissolved oxygen (DO) levels in culture ponds, contrary to the perception of many technicians.

Paddle wheel aerators used for shrimp bioflc ponds in Indonesia and Malaysia can create effective water currents reaching an optimum length of 50 m and a maximum of 60 mFor HDPE lined ponds, the current could reach an optimum depth of 1.4 m and a maximum of 1.5 m only. With this level of effiiency, aerators need to be positioned to create optimum currents to suspend the bioflc colonies, clean pond bottom and direct sludge to the centre of the pond to facilitate siphoning when necessary.

Depending on the targeted stocking density, the number of aerators (energy input) and the correct positioning of the aerators are crucial. In shrimp biofloc systems, only 10% more aeration is needed if compared to phytoplankton system to provide available dissolved oxygen for heterotrophic bacteria. In addition, aeration using air blowers can also be applied.

The basic concept on currents created by aerators is that these currents do not block or cross (horizontal or vertical) so that optimum effiiency of the aerators is maintained. Studies showed that paddle wheel aerators (1 hp) with current flw of 500 m will produce 500 kg shrimp/hp. Shrimp bioflc systems do not need as much aeration as in fih bioflc systems. Excess aeration capacity of up to more than 45 hp/ha with an estimated effiiency of only 250 kg shrimp/hp has been observed in many shrimp farms using bioflc system. Many technicians are not aware that there are limits to dissolved oxygen levels in pond water, regardless of how much aeration is provided. The solubility of dissolved oxygen to saturation point, in waters of different temperatures and salinities was reported by Boyd (2001). Aerating without following any basic concepts on direction or position could lead to lower growth or mortality during operations. With correct positioning of paddle wheel aerators, there should be areas for feeding and resting, and sludge collection within the pond - aspects which are essential for shrimp health.

Figure 2. Effiiency of paddle wheel aerators

Shrimp biofloc technology
For optimal and sustainable commercial biofloc shrimp culture, HDPE or concrete-lined ponds are basic requirements. High stocking densities of 130-150 post larvae/m2 and high aeration rates of 28-32 hp/ha are also essential for a production of more than 20 tonnes/ha. Energy effiiency is 680 kg/hp and can be as high as 1,000 kg/hp with partial harvesting. A maximum production of nearly 50 tonnes/ha has been achieved with stocking density of more than 250 post larvae in small HDPE lined ponds (Taw, 2005; Taw, et al 2008).

Taw (2014 and 2015) gave details for simple operational protocols on shrimp bioflc technology for commercial scale shrimp culture in large ponds. To achieve best results, only specifi pathogen-free post larvae should be stocked. Using Imhoff cones for assessment, biofloc volumes need to be maintained below 10 mL/L for full biofloc and 5 mL/L for semi-bioflc systems. Green or brown water is acceptable, but black water is an indicator of abnormal conditions. Grain pellets and molasses supply carbon as needed. Generally, grain applications vary from 15 to 20% of  the total feed used during operations at the early culture stages and increases to 25 to 50% nearer to harvesting. This depends on whether the system is full or semi-biofloc.

                       Figure 3. Positioning of paddle wheel aerators in 0.5 ha pond
              (15 hp/0.5ha)

Dissolved oxygen concentrations need to be monitored frequently to keep levels higher than 4 mg/L. Particularly in biofloc systems, aerators need to be constantly monitored for malfunctions and repaired or replaced without delay, as the aerators need to operate at least 22 hours a day. The suspended biofloc must be readily available as feed for shrimp. Pelleted grain, a mixture of ground wheat, corn and soy with a protein level between 14 and 18%, and molasses are used to sustain C:N ratios above 15. This provides an inexpensive organic substrate on which bioflcs can develop, in addition to increasing C: N ratio. Shrimp feed could be high (35 to 40%) or low (29 to 30%) in protein. Molasses can be applied two or three times per week at 15-20 kg/ha. In addition to typically used chemicals such as dolomite and lime, kaolin applied at 50-100 kg/ha is required in the preparation of pond water and during operations. Kaolin particles suspended in pond water are thought to become the nucleus of the bioflc community in pond water.

Biofloc technology for biosecurity
Biosecurity or bioflc technology per se cannot prevent or control emerging shrimp diseases such as white spot syndrome virus-WSSV, infectious myonecrosis virus-IMNV or early mortality syndrome/acute hepatopancreatic necrosis disease- EMS/ AHPND. With emerging new viral diseases such as EMS/AHPND in Asia, preventive solutions have become essential for sustainable production in shrimp farming.

Biofloc technology was used in Indonesia without incidences of WSSV when this was a threat to shrimp farmers during the early 2000s (Taw, 2005 and 2011; Taw et al, 2010, 2011 and 2013). In the late 2000s, IMNV outbreaks in Indonesia caused huge losses to Indonesian shrimp farmers, before bioflc technology was adopted. During this time, a small shrimp farm in Northern Bali using appropriate bioflc technology protocols with strict bio security did not succumb to shrimp disease (IMNV, Taw and Setio, 2014). In Malaysia, bioflc technology was applied at the Blue Archipelago shrimp farm from October 2011 and since then is operating successfully without any incidence of EMS/ AHPND (Taw, et al. 2013 and 2014). Shrimp farming with bioflc technology and disease prevention control was published by Taw (2014 and 2015).

In summary, fild experiences has indicated that with strict biosecurity, energy effiiency and applying correct bioflc technology protocols, shrimp farms have much higher probability of effiient and sustainable production.

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