66 SEPTEMBER 2016 • WORLD AQUACULTURE • WWW.WAS.ORG Nursery Raceways for Rearing Pacific White Shrimp Nursery raceways to raise shrimp from PL10-15 to 2-3 g is a good approach for shrimp farmers to improve survival of shrimp in growout systems. Being the crucial phase of rearing, farmers will benefit by procuring seed from such raceway based nurseries because there is high risk to stock PL10-15 directly into grow-out ponds. Indoor nursery raceways are technically feasible and a potentially viable system economically as an approach to combat emerging pathogens in shrimp farming (Tables 1-3). Three advantages of this system are high output, efficient use of land and labor, multiple crops per year, lower cost per water volume and biosecurity assuring the health of the target crop by blocking introduction of excludable pathogens. An added advantage of zero water exchange driven technology is the enhancement of shrimp growth by microbial floc. (Fig. 1). Air is supplied by three 5-hp blowers that operate alternatively every three hours. Water circulation in raceways depends primarily on airlift pumps. Air is introduced at a depth of 30 cm to attain a maximum uplift of water through a vertical PVC pipe, which has a 90o elbow at the top. Water is lifted through the pipe from the bottom and is directed through the elbow in the desired direction to develop unidirectional water flow in the raceway. There are six airlift systems in each raceway, with three on each side of the central baffle, and each set is provided with three airlift pipes. Airlift pumps are fixed to wooden crossbeams with stainless steel screws that allow adjustment of the height of the airlift pump discharge in raceways when water level is low. A rapid sand filter (Waterco, Australia) with manual backwash and a water filtration capacity of about 20 m3/h was provided for each raceway. The sand filter can be used to filter incoming seawater or raceway water. The main water circulation bypasses the sand filter. Raceways (40 m3) using biofloc technology for nursery rearing of Pacific white shrimp. Checking the concentration of biofloc using an Imhoff cone. Settled biofloc in Imhoff cones. Stocking Pacific white shrimp post-larvae into biofloc nursery tanks. Nursery raceways to raise shrimp from PL10-15 to 2-3 g is a good approach to improve survival of shrimp in grow-out systems because there is high risk to stock PL10-15 directly into grow-out ponds. Advantages of this system are high output, efficient use of land and labor, multiple crops per year, lower cost per water volume and biosecurity.
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