32 SEPTEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG significant reduction of total nitrogenous losses, clearly associated with lower metabolic losses (Fig. 3) and an increase in pepsin activity (Fig. 4). In another trial, Digestarom® was tested on Pacific white shrimp Litopenaeus vannamei at the Pearl River Aquaculture Institute, China. In this trial, supplementation of shrimp diets with Digestarom® resulted in an enhanced shrimp weight (+14 percent) and improved feed conversion (-11 percent) (Fig. 5). Beyond the clear positive effects on improving feed efficiency, nutrient sparing could be a powerful solution to limit nitrogen discharge to the environment. Phytogenic feed additives decrease ammonia emissions through improved protein use, reducing the loss of nitrogen to the environment. Phytogenics as a Tool for Preventive Health Management It is well documented in the literature that phytogenics can have a positive effect on innate immunity factors such as nitric oxide and total complement, which are important indices of the ability of host immune defense mechanisms to manage infections. The active antimicrobial components of phytogenics can act in several ways: they may lyse the bacterial cell wall, block protein and DNA synthesis or inhibit enzyme secretions and interfere with the signaling mechanism of quorum sensing pathways. Pathogenic microorganisms have a major impact on commercial shrimp production. Any measures that support shrimp resistance to pathogenic challenges are urgently required. In a trial carried out at the Pearl River Aquaculture Institute, the effect of Digestarom® on disease resistance in white shrimp was evaluated. In this trial, after a supplementation period of 56 days with Digestarom®, shrimp were injected with 0.2 mL of Vibrio parahaemolyticus at 5 x 107/mL. Time of death and quantity were recorded every 4 h. Shrimp fed Digestarom® had increased resistance against V. parahaemolyticus in comparison with the control (Fig. 6) and improved immune parameters and resistance to free radicals (Fig. 7). Compared to the control group, mortality of shrimp fed the matrix-encapsulated phytogenic feed additive was maintained at around 20 percent, while mortality rapidly increased in the control group. Phytogenics and Fillet Quality Another prospective area for the use of phytogenics in aquaculture is improvement of the anti-oxidative status of fish fillets. Fish, more than ever, are appreciated because some have high levels of unsaturated fatty acids, but these can be easily oxidized. Antioxidants are an important factor for limiting oxidation of fatty acids in the flesh after slaughtering. Lipid oxidation can cause faint and pale color, low water holding capacity and reduction in nutritional quality of the fillet. Phytogenic products have the ability to scavenge free radicals by single-electron transfer and are thus excellent feed additives to improve fillet quality. For this purpose, a trial with rainbow trout Oncorhynchus mykiss was carried out at a commercial trout farm in Karditsa, Thessaly, Greece. Malondialdehyde (MDA) was chosen as an indicator of oxidation stability and glutathione-S-transferase (GST) was used as an indicator of auto-oxidation. The levels of glutathione peroxidase and MDA were evaluated on the day of slaughtering and after five days of refrigerated storage. Inclusion of Digestarom® TOP, FIGURE 4. Pepsin activity in sea bream as affected by supplementation of matrix-encapsulated Phytogenics (Digestarom® P.E.P. MGE). Bars differs significantly (p<0.05). Source: Biomin trials (2012). BOTTOM, FIGURE 5. Effect of Digestarom® P.E.P. MGE on white shrimp final weight and feed conversion ratio. Source: Biomin trials (2012). TABLE 1. Effects of experimental diets on the antioxidative status of trout fillets after refrigerated storage. Values in the same column with a different superscript symbol differ significantly (p<0.05). Source: Biomin trials (2012). MALONDIALDEHYDE (nmol/mg product) GLUTATHIONE S-TRANSFERASE (nmol/min product) Day 0 of storage Day 5 of storage Day 0 of storage Day 5 of storage Control 34.1 49.1a 2.12a 1.28a Digestarom® 30.2 32.3b 2.84b 2.39b P.E.P. MGE
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