Application of enzymes in aqua feeds
Aquatic animals lack certain digestive enzymes during early development or throughout their lives. In the case of larvae lacking some enzymes, providing these enzymes give the animals a better chance of thriving on feeds.
The objective of this article is to present a summary of findings from studies on enzyme application in aquatic animal feeds, and to provide other useful information for those who want to consider using enzymes in feeds.
Early studies on enzyme applications in fish were conducted with enzymes extracted from fish intestine. Addition of proteolytic enzymes from fish in common carp diets resulted in only small positive effects (Dabrowska et al., 1979; Dabrowski & Glogowski, 1977 a,b).
The starch-digesting enzyme, alpha-amylase, when added at the rate of 0.2 percent, resulted in better growth and increased food conversion rate of trout (Tomassion et al., 1982). However, Carter et al. (1992) reported lack of Atlantic salmons' response to alpha-amylase supplementation.
Even if enzyme extracts from fish had worked better, it would not have been practical to rely on enzymes from fish for dietary applications. Purification of enzymes from intestinal extract is not only hard to scale up but also expensive. Microbial fermentation technology presents a more realistic way to produce enzymes.
While adding live microorganisms to diets to produce enzymes is possible in specialty feed applications, large-scale commercial enzyme applications rely on enzymes produced by microbial fermentation technology.
The application and benefits of phytase in animal species is well documented. Up to 80 percent of phosphorus in plant seeds is in the form of phytate. This form cannot be digested by the intestinal enzymes of animal species.
Cheng & Hardy (2002) showed that microbial phytase supplementation of diets at 500 units per kg diet containing barley, canola meal, wheat and wheat middlings improved availability of energy and phosphorus in rainbow trout.
Debnath et al. (2005a) showed that phytase at 500 units per kg feed gave higher weight gain, apparent net protein utilisation and energy retention value in Pangasius pangasius fingerlings.
Liebert & Portz (2005) reported better growth, feed conversion ratio, protein efficiency ratio and mineral deposition in juvenile Nile tilapia, Oreochromis niloticus, fed diets supplemented with microbial phytase.
Application of enzymes is probably a solution to high larval mortality in aquatic animals. The intestinal tract of aquatic animal larvae is shorter and relatively undeveloped when compared with that of the adults. Not all enzymes necessary for digestion are produced in the gut of the larvae and it has been suggested that enzymes present in live food consumed by the larvae aid in digestion. This follows then, that larval feeding would benefit from enzyme application.
While considering effectiveness of enzyme applications, one must also take into account findings that have shown no impact of enzyme application on fish or shrimp performance (Carter et al., 1992; Carter et al., 1994; Buchanan et al., 1997; Divakaran & Velasco, 1999).
Other than the likelihood that species-related differences exist in enzyme effectiveness, it is also possible that ingredients used in diets determine whether an enzyme is effective or not.
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Article made possible through the contribution of Feedware.com and Aquafeed.com.