Dr Yoram Avnimelech, Technion, Israel Institute of Technology introduced bioflc technology (BFT) for intensive farming of both fish and shrimp. Avnimelech, an expert in BFT has coauthored three practical guides on the technology. The third was recently published in 2014.

“Aquaculture has to be more effiient in the use of water resources and one direction is in intensive aquaculture in closed systems with zero or low water exchange. However, the high biomass means high accumulation of organic matter: as in the case of shrimp, for each kg of feed with 35% protein and 54 g of nitrogen, 38 g is excreted into the water. In conventional systems, to remove nitrogenous wastes, the options are water dilution, using plant and algae to consume the nitrogenous wastes or nitrifiation by autotrophic bacteria. This means that culture water needs to be recycled through a series of biofiters to treat the water adding up to costs in production.”

“The principles of BFT include: zero or minimal water exchange; the development of a dense microbial population as part of the pond ecosystem; and a carbon to nitrogen (C:N) ratio of 15 to control inorganic nitrogen concentration in the water. Water treatment depends on the control of heterotrophic bacteria with the culture component in tandem with nitrifying bacteria and algae. In addition, feed nutrients are recycled, doubling the utilisation of protein.”

 Avnimelech compares BFT with an external biofitration systewhich is effective in removing nitrogenous wastes but at a high cost. “BFT is best explained as an integrated system within a pond. The bioflcs are an ecological niche containing bacteria, algae, protozoa and zooplankton feeding on fih culture residues and recycling the feed within this niche. Bacteria are small but a dense population join together in a flc. It is possible to change the size composition of bacteria in a flc. We can use microbes to degrade the wastes, part of it to carbon dioxide and about 50% to microbial biomass.

 “On how much carbon is required, Avnimelech said that 20 g of carbohydrate such as from molasses, cassava etc. are needed to sequester 1 g of ammonium. “This is calculated when there is no algae and no nitrifiation. This is the maximum amount to add although often there are some algae in the pond. Adding too much is not harmful, just additional cost.”

 Commercial applications
Dr Nyan Taw, Blue Archipelago, Malaysia provided examples of how BFT is applied in commercial farms. A farm in Belize was the fist to carry out vannamei shrimp farming in bioflcs. It achieved 13.5 tonnes/ha production when conventional shrimp farming in the US yielded only 3.5 tonnes/ha. At that time, bioflc was known as bacteria flc. In the early 2000s, R&D on biofloc systems for vannamei shrimp ponds in Indonesia produced yields as high as 50 tonnes/ha/crop. The fist commercial application of biofloc in 26 semi-lined ponds yielded 22 tonnes/ha of vannamei shrimp. Feed conversion ratio was 1:1.

 “Today, using full bioflc systems, commercial production of vannamei shrimp reach 20-25 tonnes/ha/crop whilst with semibioflc systems, the average production of vannamei shrimp is around 15-16 tonnes/ha/crop. In the US, Samocha (2009), reported production of up to 12.0 kg/m3 (120 tonnes/ha) in closed super-intensive biofloc raceway systems of vannamei shrimp. Smith (2008) reported on semi bioflc systems with Penaeus monodon in Australia which yielded 10.0 to 12.0 tonnes/ha with stocking density of 45 PL/m3 from stable bioflc” said Taw.

 “What is usually misunderstood is that we start with a normal phytoplankton system. Molasses and wheat flour grain are added as the carbon source and there is a transition time of 4-5 weeks. There is actually a flctuation between algae and bioflcs in ponds; pH flctuation is narrow and alkalinity will go down. It must be clear to pond technicians that contrary to conventional farming systems, brown and foamy water in bioflc ponds are not signs of poor culture conditions and the health status of shrimp is demonstrated by shrimp actively jumping in the ponds. Biofloc populations differ in size and species composition from one pond to another.

 Taw summarised the principles in shrimp farming using BFT. “This is a system for intensive culture in zero water exchange where evaporated water is replaced by treated water. In full

bioflc systems, the stocking density is 130-150 post larvae (PL10)/m2 with strong aeration (28-32 HP/ha) using 15 paddle wheels/ha running continuously for 22/24 hours. The positioning of the paddlewheel is critical to suspend the flocs and particularly essential to centralise sludge for easy siphoning out of ponds. Biofloc is controlled at 15 ml/L. Grain pellets do not act as feed but for balancing C:N ratio at more than 15 and suspended particles provide the attachment for the bacteria flocs to form larger colonies.

 “Semi bioflc systems require a lower level of management at floc control of less than 5 ml/L. The stocking density is 80-100 PL10/m2, while paddlewheel requirement is 22-24 HP/ha.

Recently, we have discovered that shrimp farming in bioflocs can work well in HPDE lined, concrete lined as well as earthen ponds. In general, shrimp from biofloc systems have darker red colouration when cooked, with a score of 30-31 on the “Salmon scale,” said Taw.

 Both Avnimelech and Taw emphasised the advantage of the system relating to biosecurity and disease prevention, which has been supported by research output and anecdotal information. Taw quoted the case of a farm in Bali which previously had problems with white spot syndrome virus (WSSV) and infectious myonecrosis (IMNV). Since 2009, upon adoption of bioflc systems, production reached 33 tonnes/ha with no incidences of disease. The South China Sea Fisheries Research Institute in China reported that high dissolved oxygen conditions and promoting heterotrophic bacteria growth are two important methods to prevent disease outbreaks after a tropical storm in 2010.

 Biofloc as feeds
In his second presentation, Avnimelech discussed the use of bioflocs as feed within the pond system and as a feed ingredient. “Suspended bioflcs in intensive systems without or with limited water exchange carry a high feed equivalent. In ponds with a biofloc of 100 mg/L, the equivalent feed potential stored in the pond is about 1000 kg/ha. Shrimp and fih can harness this feed. Research indicated that external feed can be reduced by 20%. However, what the quantity of bioflcs consumed represents is a saving on feed costs and this is the added value of the biofloc.”

Bioflocs contribute 35-50% crude protein and crude lipid fro- 0.6 to 12% (Conquest and Tacon, 2006); according to various research, bioflcs are also able to supply enough fatty acids, vitamins and trace minerals. “However, there is a defiiency in arginine, lysine and methionine,” said Taw.

 Feed ingredient

According to Avnimelech, “In the last few years there has been an effort to use treated bioflocs as feed ingredients. We have some data indicating some ingredients of bioflocs are better than conventionally manufactured feeds. Industry looks for recipes to reproduce biofloc as feed ingredients.

 Some recent work was quoted. In Australia, Glencross et al. (2014) reported that in farm trials, monodon shrimp fed with the feed additive Novacq (from controlled production of marine microbes) grew on average 30% faster, are healthier and can be produced with no fih products in their diet. Ju and co-workers (2008) found that microbial biomass inclusion in the feed pellets raised growth rates of vannamei shrimp by 21% as compared to commercial feed.

 Published in January/February 2015 AQUA Culture Asia Pacifi Magazine