26 JUNE 2017 • WORLD AQUACULTURE • WWW.WAS.ORG Vertically Integrated Farm Design Chambo Fisheries operates a vertically integrated farming operation that includes a quarantine facility, broodstock pairing tanks, an artificial incubation room for hatching eggs collected from female brooders, a dedicated nursery system, purging tanks, a moist feed milling plant, an ice plant and cold-storage facilities apart from the Biofloc Technology (BFT) grow-out tanks. Figure 4 details the farmed production cycle of Shiranus tilapia at Chambo Fisheries. The farm has eight large round-ended (R-ended) grow-out tanks, each holding 780 m3 of water and capable of producing up to 100 t of tilapia per tank in a year, or up to 130 kg/m3 of effective rearing volume per year via a multi-cohort sequential production schedule, although rearing densities average only around 20 kg/ m3. Because of the cool climate near Blantyre at 1130 m above sea level, all production facilities require placement within greenhouse enclosures. Supplemental heat is sourced from shallow solar ponds (SSP) coupled to a hydronic heating system that includes stainless steel heat exchangers built into the tank floor that are regulated by thermostatically actuated heat exchange pumps. The design of the R-ended BFT grow-out tanks by SAFF at Chambo Fisheries is novel in many respects. The tanks include a built-in lamella separator for solids capture and removal. Control over floc concentration in the water column and the retention time of fecal and organic material is achieved by regulating water flow through the lamella separator from a full-width floor drain in the main tank. Water is pulled through the lamella separator through development of a water head differential at the far end of the central channel by using a multiple-pod airlift pump that permits flexible control over water pumping rate. Every aspect of the BFT R-ended tank design aims to minimize capital and operating costs, taking full advantage of the superior hydraulic environment created by the integrated R-ended tank design, creating a beneficial streaming effect while improving the driving concentration gradient for oxygen transfer by carefully selected and positioned aeration devices. Forced moderate exercise has been shown to induce muscle hypertrophy, improve growth rates and reduce the energetic costs of protein accretion. Fish that are fed under continuous moderate exercise exhibit a shift in metabolism to derive energy for swimming activity largely from carbohydrates and lipids rather than protein, a survival mechanism to spare protein loss from the muscle. This results in fish at harvest with a lower fat content while FCRs are reduced, growth is enhanced, flesh texture firmness is improved, and fillet yields are elevated marginally (more plump fish relative to their body lengths). Horizontal water velocity control in the range 15-30 cm/sec is achieved by adjusting the submergence depth of the paddles on paddlewheel aerators. Multi-cohort Production The farm design has been tailored to take advantage of the benefits of continuous sequential production where each grow-out tank is stocked and harvested every three weeks. This production strategy is enabled by using screened compartments (Fig. 5) where fish are moved in a conveyer fashion every three weeks to a larger compartment using simple crowding screens. This management technique results in production output yields of 4.6-5.8 t every three weeks. This elevates the production to capacity (P:C) ratio to 5.5-6.2, indicating the high rate of crop turnover relative to system carrying capacity. The use of a multi-sequential, multi-cohort production system in essence doubles output production and halves input power costs in comparison to batch production, which yields an effective P:C ratio of only 2.4. Economic viability is greatly enhanced due to the doubling of production output based on the same investment in equipment and infrastructure compared to a batch production system. This unique innovation by SAFF, called the SAFF One-Tank Husbandry Approach, was first pioneered by the company in the Middle East on two RAS farms and a third RAS farm in Malawi. Shiranus tilapia reach an average marketable weight of 218 g in 189 days from hatch at a temperature range of 27-29 C. Although purging fish to improve flavor quality is practiced, it is unnecessary in well-managed BFT systems because the fish carry no off-flavors or flavor taints. Fish are sold whole on ice and no processing takes place on site. Specialized Feeds Produced On Site Feeds — including broodfish diets, starter feeds and specialized C/N ratio feeds — are produced on-site using a low-cost moist-pellet milling plant that produces sinking pellets of medium to low water stability. The major components of the Chambo Fisheries feed plant include a hammer mill and a combination grinder, mixer and moist feed pelletizer, and a horizontal dryer and grading sieves for starter feed production on-site. Feeds for fish >5 g are all animal protein-free and are based FIGURE 3. A battery of eight 766-m3 multi-cohort sequential SAFF-BFT grow-out tanks at Chambo Fisheries near Blantyre, Malawi. FIGURE 2. A schematic of the process of biofloc technology to promote nitrogen uptake via heterotrophic bacteria that becomes a food source for tilapia and shrimp.
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