36 MARCH 2017 • WORLD AQUACULTURE • WWW.WAS.ORG In terrestrial livestock, one way to reduce fat content is to incorporate beta-adrenergic agonists, such as ractopamine, in the feed. Beta-agonists are organic molecules that activate protein synthesis and decrease protein degradation at a cellular level, and ractopamine is efficient at reducing fat content by increasing lean mass gain in swine and cattle. Limited information is available on the use of ractopamine in fish, so we designed two trials to test the feasibility of using ractopamine as a lipolytic feed additive in tambaqui diets. The first trial determined the rate of tissue deposition during the production cycle of tambaqui in net cages and the timing for use of ractopamine. The second trial tested if dietary FIGURE 5. Location of trial 1 (Pôr do Sol Farm). (Source: Adapted from Wikipedia and Google maps). TABLE 1. Composition of basal dieta (as fed). Ingredients g/kg Soybean meal 579.4 Corn gluten meal 42.0 Fish meal 16.4 Corn 90.0 Wheat middlings 151.0 Broken rice 50.0 Cellulose 5.9 Soybean oil 20.0 Dicalcium phosphate 25.7 Limestone 7.0 Ascorbic acid 2.5 NaCl 0.7 Vitamin/mineral mixb 5.0 Antioxidantc 0.2 Total 1000.0 a Digestible protein: 286.9 g/kg, lipids: 45.7 g/kg, crude fiber: 57.0 g/kg; digestible energy: 13.81 Mj/kg. b Vitamin and mineral mixture, provided the following per kg diet 1: vitamin A, 16060 IU; vitamin D3, 4510 IU; vitamin E, 250 IU; vitamin K, 30 mg; vitamin B1, 32 mg; vitamin B2, 32 mg; calcium pantothenate, 80 mg; niacin, 170 mg; biotin, 10 mg; folic acid, 10 mg; vitamin B12, 32 µg; vitamin B6, 32 mg. c Antioxidant is butylhydroxytoluene (BHT). FIGURE 6. Growth curve (a) and tissue deposition (visceral, liver, muscle and celomatic fat) (b) of tambaqui raised in net cages for eight months (n=10). a. b. FIGURE 8. The effect of dietary ractopamine supplementation on (a) visceral fat index (VFI) and (b) hepatosomatic index (HSI) of tambaqui (n=3). FIGURE 7. The effect of dietary ractopamine supplementation on (a) visceral fat index (VFI) and (b) hepatosomatic index (HSI) of tambaqui (n=3). a. b. c. d. a. b. FIGURE 9. Hepatic alanine (a) and aspartate transaminase (b) activity of tambaqui fed diets containing graded levels of ractopamine for 30 days (n=3). a. b.
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