WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2017 25 assimilation into new bacterial cell biomass. BFT simultaneously provides an abundant source of “bacterial plankton” and a rich source of goodquality protein and nutrients for filter-feeding fish and shrimp — BFT is then rather like killing two birds with one stone. Figure 2 provides a schematic of the process of Biofloc Technology (BFT) to promote nitrogen uptake by heterotrophic bacteria which then becomes a food source for tilapia and shrimp. Experience raising tilapia in BFT, where feeding rates per unit area are at least 4 to 5 orders of magnitude greater than shrimp BFT systems, is limited. Knowledge gaps remain about BFT engineering economics, tilapia feeding systems and bioenergetics, cost factors and the economics of this new technology relative to conventional tilapia aquaculture systems. Insightful experience gained at Chambo Fisheries fills many of these knowledge gaps. Chambo Fisheries Chambo Fisheries is purportedly the world’s largest tilapia biofloc technology (BFT) tank farm and the largest such tank farm in Africa, located on the outskirts of Blantyre, Malawi (Fig. 3). The farm became operational in 2013 based on the mandatory production of Mozambique tilapia Oreochromis mossambicus and Shiranus tilapia O. shiranus due to restrictions that forbid the importation and culture of farmed breeds of Nile tilapia O. niloticus in the country. Despite the slow growth of Mozambique and Shiranus tilapias, compared to the best farmed breeds of Nile tilapia, good flavor quality without purging, low feed conversion ratios (FCRs), yearround production potential (upon completion of a shallow solar pond supplemental heating system) and favorable economic factors has Chambo Fisheries poised for expansion regionally. The system design was developed by the author of this article in his capacity as Chief Technical Officer of SustAqua Fish Farms (Pty) Ltd. (SAFF), a South African concern, who developed the farm blueprints, production schedules, management systems and executed start-up, monitoring and management training. Malawi — a Fish Eating Nation Although Malawi is endowed with the ninth largest lake in the world and the third largest and second deepest lake in Africa, overfishing resulted in the collapse of the tilapia fishery around 19901991. Tilapia, known locally as chambo, is the country’s favorite fish and now costs from US$ 4.00-8.00/kg (R55-110/ kg) for whole or live fish. This is a result of market scarcity which is unfortunate considering the massive demand for the fish and its abundant availability at very affordable prices (< US$1.50/kg) prior to 1990. Population growth at nearly 3 percent per annum in Malawi since 1990 has put the anticipated supply shortfall of fish in the country at around 80,000 t for 2017 based on sustaining 1990 per capita supply levels. Tilapias are the preferred fish and the national dish in the country. A substantial market exists for producers capable of providing whole fish more competitively than dressed broiler chickens, less than a cost of US$2.40/kg (R33.00/kg) in Malawi. Under favorable economies of scale and scope, tilapia production using biofloc technology represents an attractive investment proposition if that selling price can be matched. Biofloc Technology Biofloc Technology (BFT) is a relatively new and potentially revolutionary technology that is especially productive for tilapia and shrimp aquaculture. BFT is a sustainable and environmentallyfriendly method of aquaculture that controls water quality and harmful pathogens along with providing value-added production of microbial protein feed for the aquatic farm system. Bioflocs are clustered aggregations of microbial communities such as phytoplankton, bacteria, and living and dead particulate organic matter (Fig. 1). Shrimp and tilapia especially benefit from BFT due to their ability to filter-feed on floc in the water column, thereby reducing feed costs by improving feed conversion. The beauty of BFT is in the mechanisms for ammonia removal from water. Using feeds with a carbon to nitrogen (C/N) ratio greater than 15 results in the dominance of heterotrophic bacteria as the major pathway for the removal of toxic nitrogenous compounds via Large-Scale Biofloc Tank Culture of Tilapia in Malawi – a Technical Success Story Ray Kourie FIGURE 1. Imhoff cones are used to measure biofloc volume in BFT tanks at Chambo Fisheries. (CONTINUED ON PAGE 26)
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