14 JUNE 2015 • WORLD AQUACULTURE • WWW.WAS.ORG (4-20 m3) to larger (>100 m3) cages, 2) starting grow-out with juvenile fish (10-30 g), vaccinated or not, which has reduced risk in production and 3) size-grading tilapia over the grow-out cycle when disease or environmental stress factors do not affect production. Sex-reversed tilapia are usually sold to farmers as fry (0.2-1 g). In cages, 5 to 8 weeks are required to grow 0.5-g fry to 30-g juveniles, depending on stocking density, feed and water quality. Many farmers have found it more advantageous to stock juvenile tilapia of >10 g. This has allowed farmers to purchase fish that are more consistent in body weight, more resistant during growout, requiring less size-grading and handling during grow-out. Farmers also have the option of buying juvenile fish that have been vaccinated against Streptococcus agalactiae. The movement towards larger-volume cages has been imposed by the market and the drive to reduce production costs. Because tilapia sales were mainly domestic and retail, small-volume cages allowed multiple partial harvests of small quantities of fish. However, farms moved from small- to mediumscale operations as the market started to demand larger quantities of fish. As a result, cages that could sustain larger fish biomass (>5 t) were required. Smaller cages from which less than 1 t of tilapia can be harvested are still popular, but they are becoming less economically attractive due to greater labor costs associated with feeding and management. Size-grading has become a key management strategy when stress and diseases do not affect production. Fish are usually sorted manually (Fig. 8A) but, in large operations, this procedure is mechanized (Fig. 8B). This also allows moving the stock to cages that are clean with larger mesh sizes. Fish grading is usually carried out once or twice in a production cycle. This procedure has allowed a better estimate of the stocked fish biomass, allowing producers to harvest more consistent fish sizes. Feeds and Feeding Brazil is a key global producer of grains and livestock. This has given a competitive advantage to the aquafeed industry in the country, which uses Brazilian soybean meal, corn and rendered animal by-products as major dietary protein sources. As a result, the feed industry can rely on local commodities to supply the necessary protein sources that tilapia and shrimp require. With a strong presence as a global animal feed producer, Brazil has strict technical standards and guidelines involving hygienic, sanitary and operational manufacturing procedures. As such, most feed plants have obtained GMP (Good Manufacturing Practices) certification with an accredited FIGURE 8. Manual (A) and mechanical size-grading (B) of tilapia during grow-out in farms in northeast Brazil. Photos: Alberto Nunes. A. B. FIGURE 9. Industrially available shrimp and tilapia feeds in northeast Brazil are mostly sinking (A) and floating extruded (B) pellets. Photos: Alberto Nunes. A. B.
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