WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2016 65 a live nutrition source. Recycling of nitrogen within the system in the form of microbial protein improves feed efficiency. Biosecure raceways involve a combination of physical, chemical and biological measures like use of specific pathogen free shrimp stocks, treatment of incoming water, a greenhouse shelter, no water exchange, and an airlift system for circulation and aeration to ensure high survival and production. System Specifications To enhance survival and yield during shrimp larval rearing, concrete nursery raceways were constructed in a greenhouse. The greenhouse is 20 m long by 10 m wide and was constructed using cast iron pipe pillars, framing and roof supports. The roof consists of 80 percent non-transparent white fiberglass sheets and 20 percent transparent fiberglass sheets. Sidewalls consist of removable green shade cloth (75 percent) affixed to wooden frames. Nursery raceways are 50 m3, rectangular (15 m long × 3 m wide × 1 m deep) and lined with HDPE. Each raceway had a central longitudinal partition placed over a 5.1-cm Schedule 40 PVC pipe designed to aid water circulation. Raceways were designed to allow drain harvest. Towards the drain end of two raceways, a single harvesting tank (2 m × 1.5 m × 2 m) was provided for water exchange, bottom waste clearing and harvesting. The outlet of raceways was located halfway between the end of the partition and the raceway end wall. Perforated filter pipes were mounted on the outlet to avoid losing shrimp when water is drained. The bottom of each raceway tank was constructed with a 0.5 percent slope to allow easy draining of water. Tanks were operated with a freeboard of 15 cm, resulting in a productive volume of 40 m3. Microbial flocs remain suspended by twin-lobe air blowers (5 and 10 hp) that provide aeration for dissolved oxygen management and air for operation of airlift pump systems for continuous water circulation The global shrimp industry is facing major challenges to its sustainability from dreadful diseases and a deteriorating environment. One effective strategy is biosecurity to isolate the farm physically from its surroundings and prevent waste accumulation through bioremediation and limited or no water exchange. Biosecurity and health management are among the top priorities to be addressed for the sustainable growth of shrimp aquaculture. To achieve this, innovative technologies and investments in closed systems are essential. In response to these requirements, aerobic microbial floc raceways engineered with biosecurity are being used for the nursery rearing of Pacific white shrimp in India. Nursery Phase—A Necessary Investment Nursery culture of shrimp serves as a primary quarantine to prevent the introduction of pathogens into grow-out ponds, improving shrimp survival and feed efficiency and reducing the culture period. This improves profit potential by permitting more crops per year. Size uniformity with efficient use of grow-out tanks can be achieved by maintaining stable water quality and good feed management. A nursery phase provides an opportunity for shrimp acclimation in inland areas where water has a salinity less than 5 ppt. Aerobic Microbial Floc Nursery Raceway Technology Aerobic microbial floc technology is based on microbial protein generation accompanied by decomposition of organic matter under continuously-mixed and aerated conditions in superintensive nursery raceways. The system functions by a synergistic interaction between algal and bacterial populations in water for in situ waste treatment and bioremediation, and the production of A Biosecure Nursery System for Disease Mitigation in Shrimp Farming in India S. Felix and M. Menaga FIGURE 1. Layout of the nursery raceway complex. Biosecure raceways involve a combination of physical, chemical and biological measures like use of specific pathogen free shrimp stocks, treatment of incoming water, a greenhouse shelter, no water exchange, and an airlift system for circulation and aeration to ensure high survival and production. (CONTINUED ON PAGE 66)
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