28 JUNE 2022 • WORLD AQUACULTURE • WWW.WA S .ORG FIGURE 3. Perceived quality versus prices for the most common whitefish species (from Geldenhys 2013 and Lallemand et al. 2014). Aquaculture Stewardship Council (ASC) certified marine cultivated tilapia (izumidai) and Marine Stewardship Council (MSC) certified hoki were added above based on their market value (THAPI Aqua-Kulcha 2021b). Taiwanese marine farmed tilapia fetch a premium price of US$12/kg for fillets in Japanese sushi markets, where seawaterfarmed tilapia hybrids are called izumidai (Infofish 2003) and are sold for a price that is about 80 percent higher than the retail price of Cape hake fillets. (See Figure 3 for perceived price-quality rankings of the major whitefish species.) Exports from a future east coast marine tilapia industry are not among the objectives of the THAPI Marine Tilapia Vision 2035. The marketing of higherquality marine-cultivated tilapia aims to leverage market share rather than higher local prices or exports. A fairly sanguine outlook prognostication can be expected for this new farmed whitefish industry based upon the seawater culture of Mozambique tilapia over that of freshwater farmed tilapia due to several added advantages apart from improved texture and flavor properties: 1) Based on several studies, Mozambique tilapia use feed more efficiently, capable of achieving lower Feed Conversion Ratios in seawater over freshwater farming systems (Ron et al. 1995, Iwama et al. 1997, Barreto-Curiel et al. 2015). These advantages are further amplified by the use of Biofloc Technology (BFT) with seawater. Using all-plant based feeds with a lower protein content of just 20 percent, FCRs are anticipated to be lower than around 1, as achieved in freshwater BFT systems in Malawi (Kourie 2017b). 2) Reduced energy inputs of 1.05kWh/kg of farmed tilapia production output in seawater can be attributed to a higher alpha factor of 2.5 for sub-surface aeration (in comparison with a freshwater α factor of 0.92-1.0) at sea level and salinities of 32-36 ppt (Boyd and Watten 1989, Ruttanagosrigit et al. 1991, Fast et al. 1999). The main air blowers used to furnish air for diffused airlift aerators in seawater would require 29.2 kW (1.02 kWh/ kg of tilapia produced) as opposed to 39.8 kW (1.40 kWh/kg of tilapia produced) in a 250-t freshwater, multi-cohort, sequentially managed BFT tank system. 3) Efficient use of capital for infrastructure based upon an optimized design philosophy (proven on a large scale in Malawi) applying a multi-cohort sequential production schedule that improves production throughput capacity by almost 50 percent on an annualized basis under similar capital expenditure outlays (Kourie 2017a, 2017c). 4) Upstream and downstream scale and scope economies and the beneficial effects of specialization including a reduced gestation period from investment to first income. 5) More efficient use of labour and management, an effect of farm size and the manageability of fewer larger-scale grow-out production units (20 tanks each producing 250 t annually = 5,000 t/yr per grow-out farm). The value proposition in the development of a scalable and competitive marine tilapia farming industry in South Africa hinges on the use of reduced-input, all-plant based, low-protein feeds and BFT aquaculture tanks placed under greenhouse enclosures to capitalize on solar heat gains to enhance productivity (unit production/unit volume or surface area) and hence capital employed in farm infrastructure under reduced land area requirements. Farm gate production costs for large-scale BFT Mozambique tilapia aquaculture in seawater systems are anticipated to be FIGURE 4. Top quality Taiwanese seawater reared red tilapia fillets packed for the Japanese sushi/ sashimi/nigiri markets brings a premium price (US$12/ kg) to Taiwanese fish farmers. FIGURE 5. Large-scale freshwater Biofloc Technology fish farm developed by ThapiAquakulcha in Malawi where Mozambique tilapia Oreochromis mossambicus and Shiranus tilapia Oreochromis shiranus were reared, achieving FCRs around 1.1 on 20%-protein, all-plant based feeds (Kourie 2017a).
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