58 DECEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG range, only the fish weight would be needed to determine FCR and % BW fed. One can plot the weights and FCR or % BW fed values from Table 1 graphically along x and y axes. The x axis is individual body weight and the y axis is either FCR or % BW fed. A curved regression line can be drawn to best fit the data (Figs. 1 and 2). Equations for these regression lines can be generated with common graphics programs. Those equations can be used to calculate FCR and % BW fed for any fish size within the range of values plotted. Using data from Table 1 for channel catfish weight, FCR and % BW fed from Robinson et al. (1998), equations were determined for FCR and % BW fed as a function of individual body weight (Wurts 2014). With these equations, accurate FCR and % BW feeding rate can be calculated for channel catfish ranging in size from 27 to 1362 g. Moreover, these mathematical relationships As production systems for channel catfish become more intensive, feeding must become more accurate, precise and efficient. Proper feeding practices are required to ensure good growth, health and survival. Feed conversion ratio (FCR) and amount fed are key components of growth and production biology. Feed conversion ratio and percent body weight (% BW) fed are basic calculations and critical to feeding practices. Feed Conversion Ratio FCR = feed fed/weight gain. Weight gain can be determined by re-arranging the terms of the FCR equation. Weight gain = feed fed/FCR. Percent Body Weight Feeding (% BW) Feeding according to percent body weight is most commonly used when the farmer has an accurate estimate of total fish biomass in the pond. Daily feed is provided as a percent of total biomass. For feed calculations, the percent is in decimal form (e.g. 3 percent = 3/100 = 0.03). The amount fed to 100 kg of fish at 3% BW would be 3 kg daily. 3% BW = 0.03 x 100 kg of fish = 3 kg of feed. FCR and % BW fed change as fish size increases As channel catfish grow their feed intake as a proportion of their individual body weight decreases (Table 1). However, feed is not converted as efficiently, increasing FCR; that is, the amount of feed it takes to produce a kilogram of fish increases. When water temperatures are between 24 and 29 C, catfish fry will consume feed at 10 percent BW daily, and 454-g food fish will eat at a rate of 1.4% BW daily. For 27-g fish, FCR will be 1.15 and, for 454-g fish, it will be 1.95. This means that it takes 1.15 kg of feed to produce a 1.0 kg of weight gain in a 27-g catfish, and 1.95 kg of feed for a 1.0 kg gain in a 454-g fish, or 70 percent more feed for the same amount of growth. Because fingerlings and juvenile channel catfish (fish less than 227 g each) are growing fast, require more feed, and convert feed to weight gain more efficiently; producers should attempt to feed most carefully when fish are young (Wurts 2001). If one knows individual fish weight, FCR and % BW fed it is relatively simple to calculate growth at regular intervals. The difficulty is that data for FCR and % BW fed is only known for a limited number of fish sizes. For example, Table 1 only has FCR and % BW fed values for eight channel catfish sizes between 27 and 1362 g. Without more information, determining FCR and % BW values for other fish sizes within this size range would be imprecise guesswork. If a reasonably accurate method was available for calculating the FCR and % BW fed values for all catfish within a given size Using Equations to Improve Feeding and Growth of Channel Catfish William A. Wurts TABLE 1. Feed conversion ratio (FCR) and percent body weight (percent BW) consumed at various channel catfish sizes at optimum water temperature conditions (adapted from Robinson et al. 1998) Fish size (g) FCR Daily feed (% BW) 27.2 1.15 4.25 45.4 1.35 3.75 136.2 1.50 2.75 272.4 1.70 2.25 340.5 1.85 1.75 454 1.95 1.40 908 2.10 1.15 1362 2.30 1.05 TABLE 2. Calculated biweekly channel catfish growth data over 84 days. Days Fish size (g) FCR Daily feed (% BW) 0 45 1.30 3.80 14 63 1.36 3.34 28 84 1.43 3.00 42 109 1.49 2.72 56 137 1.55 2.49 70 168 1.61 2.31 84 202 1.66 2.15
RkJQdWJsaXNoZXIy MjExNDY=