30 JUNE 2017 • WORLD AQUACULTURE • WWW.WAS.ORG is difficult to determine what is actually consumed. Shrimp biomass can be estimated based on historical survival rates, cast-net sampling, apparent consumption of feed from feeding trays, density-dependent growth rates or a combination of these techniques. However, these estimation techniques may not take account of specific mortality events and variations between crops, which can result in improper feeding. Feed tables are a common way to determine feed inputs and are most accurate if adjusted for site specific conditions and feed nutrient density. Tables should be specific to shrimp size, water temperature, and the feed type used in its creation. Feed tables also do not take into consideration natural productivity that is a major source of food for shrimp in almost all production systems. While the amount and quality of natural foods is difficult to quantify it is often left out of the feeding equation. The lack of accurate biomass data further complicates the use of feed tables. Another issue with using predetermined feed inputs is that feed consumption by shrimp can vary from day to day and there is no mechanism to confirm consumption. Farmers often use feed trays to check feeding activity and examine shrimp to determine gut fullness for confirmation of feed consumption. All or part of the feed is placed on a mesh tray suspended in the pond. Feed input is adjusted by removing trays after feeding and observing the amount of feed that remains. If excess feed remains, feed inputs are reduced or if there is no feed, feed inputs may be increased. Shrimp may also pick up feed and carry it off the tray and then may or may not consume it. This can potentially result in overfeeding. There are additional technical and logistical issues with the design and deployment of large numbers of feeding trays that can influence results, including the size, shape, number and distribution of trays. Other methods to predict feed inputs use various forms of nutrient modeling where the quantity of nutrients to obtain a specific level of growth are translated into feed inputs. In its simplest form, if the expected FCR under pond production conditions is 1 and 1 g of growth is desired, then 1 g of feed per shrimp would be applied. Another simple model would use expected protein retention under a given set of conditions and shrimp growth rates to predict feed requirements. Pacific white shrimp Litopenaeus vannamei is regarded as the primary cultured shrimp species worldwide and a high-value commodity. Production of around 4.5 million t in 2016 (Anderson 2016) accounts for approximately 11 percent of the total value of all aquaculture species. As shrimp consumption is likely to increase, it is vital to develop sustainable farming practices. Feed is one the largest variable costs (40 to 60 percent) and the initial source of all waste products. Consequently, the development of improved feeding practices plays an important role in ensuring profitability and allowing the shrimp industry to expand. Proper feed management also facilitates efficient feed consumption, minimizes waste and reduces overfeeding so a thorough understanding of feed management is critical to the vitality of shrimp farms and the industry. Feed Management Feed handling Proper feeding practices begin when feed is delivered to the farm. Each batch of feed should be inspected immediately for mold, physical properties (size, pellet integrity, etc.) and a sample should be analyzed to verify nutritional composition. If the feed fails to meet minimum standards, the shipment should be refused and the manufacturer contacted immediately. Once the quantity and quality of the feed has been verified, it should be stored in a cool, dry place. In the case of bagged feed, it should be stored off the ground and in an area in with good air circulation. Whether bagged or in bulk, feed should be used on a first-in, first-out basis. This minimizes older inventory, helps prevent spoilage and ensures a fresh supply of feed. Feed input Feed management is both an art and a science and no one system works for everyone in all circumstances. It is critical to understand basic feed management concepts and how they can be adapted to specific circumstances. The average weight of shrimp and growth rates are easy to determine based on sampling, but determining the actual population or total biomass is not so simple. And while we can quantify the amount of feed that is offered, it A New Paradigm for Managing Shrimp Feeding Carter Ullman, Melanie Rhodes, Terry Hanson, David Cline and D. Allen Davis Shrimp harvested from the Auburn University feeding method trial. Photo: Carter Ullman.
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