10 March 2009 Table 3. Feeding chart for hypothetical fish. Values are in percent of body weight fed per day. Mean fish weight (g) 4.4-5.6ºC 6.1-7.2ºC 7.8-8.9ºC 0.9 3.6 4.8 6.9 1.4 3.5 4.7 6.5 2.3 3.4 4.6 6.1 4.5 3.2 4.5 5.7 5.6 2.9 4.3 5.4 8.2 2.7 4 5 11.3 2.5 3.8 4.6 13.6 2.2 3.5 4.3 22.7 1.9 3.1 4 31.8 1.6 2.7 3.7 38.6 1.4 2.4 3.2 45.4 1.3 2 2.9 68.0 1.2 1.8 2.5 79.4 1.1 1.6 2.3 90.7 1 1.5 2.1 181.4 0.9 1.3 2 317.5 0.8 1.2 1.8 454.0 0.7 1.1 1.7 Introduction to Feed Budget As we said, too little or too much feed going into ponds results in both biological and economic problems. When a farmer buys feed from a commercial source, the manufacturer will often include information about feeding rates and schedules. This will include what feed sizes should be for fish of different sizes (small fish are fed small granules, while big fish get large pellets) and the frequency that the fish should be fed (young fish are fed more often than older, larger fish); feed size and frequency are critical, but will not be considered in this exercise. The other information that you need, which again will typically be supplied by the feed manufacturer, is how much feed should be used per day. This is dependent on fish species, size/age and water temperature, all of which are factors determining the food conversion ratio (how much feed is needed to increase the weight of the fish by a given amount). In Table 3, a feeding chart for a hypothetical fish is shown. For any species, there is an ideal temperature for growth, and if growth is optimized, feed intake will be at its maximum to support that growth. Like many animals, commercially cultured fish need proportionately more feed when they are small, and less as they grow. Note, for example, that at 4.4-5.6ºC, fish weighing 0.9 g should get 3.6% of their body weight in feed each day, but large fish of 0.45 kg only need 0.7% of their body weight in food daily. To use Table 3, let’s say that you do a population inventory using marked fish and estimate that a pond has 5,000 fish. Based on the fish sampled you determine that the fish have an average weight of 13.6 kg; you also know that the average water temperature is 6.1ºC. Looking at Table 3, you see that the fish should be fed 3.5% of their body weight each day. Since there are 5,000 fish, with an average weight of 13.6 kg, you calculate that there are 68 kg of fish in the pond, and, therefore, 2.38 kg of feed per day are needed. In practice you can’t do daily inventories, and average fish weights will rarely match the table values exactly. While it is possible to use interpolation to calculate feeding rates, in many instances it is safer and easier to simply use a little less feed, since this will probably increase the digestive efficiency. It’s also worthwhile mentioning that slavish adherence to manufacturer feed charts is probably not in the best interests of the farmer, who should experiment a little and fine tune the feeding regimen for the particular situation.
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