WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2017 31 (CONTINUED ON PAGE 32) Feeding practices Once the proper feeding rate has been determined, feed needs to be applied in a way that allows efficient consumption by shrimp. Efficient feed consumption relies on availability of feed at the right time in the right location. Feed can be applied by broadcasting (manually or mechanically) or by placing it on feed trays. Shrimp, because of their size, are assumed to move in a smaller area than fish, limiting their ability to move across a large pond to feed. This assumption implies that feed should be broadcast across large areas and/or numerous feed trays should be deployed to improve access. However, there is little data to support a specific number of trays that should be used or what proportion of the pond area must be covered with either feed trays or dispersed feed. Several studies have demonstrated that increasing the number of feedings can improve growth by increasing nutrient availability. Shrimp are continuous grazers and begin to digest feed almost immediately upon consumption. They do not store a large quantity of feed in the stomach. Feed intake is related directly to the amount of time that feed is available (Fig. 1). However, increasing the duration that feed is in the water, the more it will break down and more nutrients will be lost (Goddard 1996, Davis et al. 2006). With more feedings, feed intake is increased and the feed is fresher. In Asia, where four or more daily feedings are used, shrimp growth rates tend to be greater than in the Americas, where farmers tend to feed twice daily. Obviously, increasing the number of feedings increases labor cost and requires more time. Reconsidering Shrimp Feeding Efficient feeding is as much an art as it is a science. Traditional feeding techniques are site specific, lack critical control points, and are labor intensive. If feeding techniques for shrimp are to evolve, we must invest in standardized studies and develop technologies to permit improved monitoring. Using automatic feeders addresses the labor required to increase the number of feedings, but continues to require manual calculation of feed inputs, setting time intervals and observations of consumption. The AQ1 (Tasmania, Australia) feeding system improves on the automatic feeder by incorporating feedback from the shrimp. A hydrophone is used in the pond to monitor feeding response each time feed is added to the pond (Fig. 2). Sounds detected by the hydrophone are relayed to a computer system for analysis. The computer and feeding software uses the information to determine when and how much to feed (Fig. 3). This has the potential to improve the use of feed by only applying it during periods of active feeding. The AQ1 system is used in multiple countries around the world and experience on commercial farms indicates that its use increases shrimp growth by 23 percent and decreases FCR by 20 percent (Bador et al. 2013). Feeding Method Study To verify these claims, Auburn University performed a study that compared the use of standardized feeding input with feed broadcast twice per day, automatic feeders distributing feed six times per day, and the AQ1 feeding system that used acoustic analysis to provide feed on demand. The four treatments used to evaluate the potential for automation were; 1) a standard feeding protocol (SFP), 2) the SFP plus a 15 percent increase in daily ration for the final 8 FIGURE 1. Feed consumption of individual 5-g shrimp over time. The graph demonstrates the direct relationship between the time feed is available and the amount of feed that is consumed. FIGURE 2. The AQ1 feedback system uses a hydrophone to record the feeding response of the shrimp and then analyzes it to determine the appropriate feeding rate (Bador 2013). FIGURE 3. The hourly feeding rate is determined by an activity index that is calculated from the feedback recorded by the hydrophone. (The response is indicated by the red line.) The rate can change throughout the day as the shrimp consume more or less feed. The high activity levels between 2000 and 0700 h result from nighttime aeration and is an artifact of the small pond size.
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