Acidifiers in aquaculture - a key to sustainable fish and shrimp production
Public opinion and regulation authorities in most export countries focus now on antibiotic abuse in aquaculture and public attention has shifted towards production methods (LuckstÃ¤dt, 2005). Furthermore, the EU has banned all antibiotic growth promoters from livestock production with effect from January 2006.
Due to the abovementioned facts, alternatives needed to be found. Several feed additives, including acidifiers consisting of organic acids and their salts may be a promising alternative for the use of in-feed antibiotics in aquaculture.
In animal nutrition, organic acidifiers and their salts exert their performance promotion effects via three different ways, as currently reviewed by Freitag (2006): in the feed, in the gastro-intestinal tract and due to effects on animal metabolism.
Even under good hygienic environmental conditions, aqua-feed may be infected with a certain amount of fungi, bacteria or yeast. In favourable conditions, such microbes can multiply rapidly during storage, especially at higher moisture levels (>14 percent) due to high humidity and a warm environment.
Conserving agents reduce microbial growth and thus lower the uptake of possibly pathogenic organisms by the fish or shrimp. Besides hygienic effects, reduction of the acid binding capacity of feed ingredients can promote animal performance. A high crude protein content of feed usually ensures rapid fish growth in juveniles, but also generates a high dietary buffering capacity at the same time and hence reduces free hydrochloric acid in the stomach.
Pepsin activation and pancreatic enzyme secretion are therefore reduced and nutrient digestion is impaired. Lowering the dietary buffering capacity with in-feed acidifier has beneficial effects on feed digestion (Eidelsburger, 1997).
The mode of action of organic acids in the intestinal tract acts in two different ways:
As mentioned above, inadequate pH reduction in the stomach inhibits pepsin activity and thus protein digestion is impaired. Effective proteolytic activity requires a pH below 4 and is still increased at lower pH values. Positive effects of organic acids on protein hydrolysis have been demonstrated (Mroz et al., 2000).
Organic acids and their salts exert growth inhibiting effects on stomach and gut microbes through pH reduction and anion and proton effects in the microbial cell. Low pH also forms a natural barrier against ascending microbes from the ileum and large intestine. On the other hand, acid tolerant beneficial Lactobacillus spp. seems to be unaffected or may even be enhanced in number (Hellweg et al., 2006).
As the energy content of organic acids is completely used in metabolism, it should be considered in energy calculation of feed rations.
Acid preservation of fish and fish viscera to produce fish silage has been a common practice and its final product has been widely used in fish feeds with reported beneficial effects (Gildbert and Raa, 1977; Ã…sgÃ¥rd and Austreng, 1981).
The scientific community has investigated the direct effects of these short-chain acids on fish feed. Several studies have been conducted with various carnivorous and herbivorous species.
In conclusion, the use of organic acid salts or acid blends is an interesting option to promote performance of a wide variety of aquaculture species worldwide.
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Article made possible through the contribution of Biomin.