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FEATURE

The use of taurine in fishfeeds

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International Aquafeed caught up with the Research Associate for the School of Fisheries, Aquaculture, and Aquatic Sciences at Auburn University, Dr Guillaume Salze, PhD, to discover what adding taurine to fish feed could mean for the industry

fter many years of research, the Association of American Feed Control Officials (AAFCO) has now approved the use of taurine in fish feeds. Taurine is an organic compound that is widely distributed in animal tissues. It is a major constituent of bile and can be found in the large intestine, accounting for up to 0.1 percent of total human body weight. The chemical compound is named after the Latin Taurus, meaning bull or ox, as it was first isolated from ox bile in 1827 by German scientists Friedrich Tiedemann and Leopold Gmelin. Dr Salze has been a research associate at Auburn University, Alabama since September 2012 having previously been a postdoctoral fellow ay the University of Guelph from July 2009. He has written or been involved in over 20 publications in the aquaculture industry. He explained that, “The Association of American Feed Control Officials (AAFCO)’s members include both public officials and industry partners. One of their roles is to provide guidelines for animal feeds and establish ingredient definitions. This new announcement is to inform the public that AAFCO amended its definition of crystal taurine – that is the species and limitations within which it can be used as a feed ingredient. The previous definition included cats, dogs, and chicken. The amended definition now includes all species and all life stages of fish.”

What is the relevance of taurine to fish feed?

Dr Salze expands, “Taurine is found ubiquitously in all animals – it is actually one of the predominant amino acids in animal tissues. For a long time, taurine was thought to be a non-essential nutrient – that is a substance that the body can make on its own using other molecules, and therefore is not required in the diet. For over a decade, a number of research groups have looked at the role of taurine in fish. As it turns out, taurine is an essential nutrient for many fish species, so it must be found in their food. If taurine is not present in the food, the fish do not eat or grow well, are more susceptible to diseases, and have increased mortality. So taurine is extremely important in these species.” Describing how this amendment will benefit both the fish stock and producers, Dr Salze reinforced that it will have a far-reaching impact. He remarked that since taurine is found in all animal tissues, animal-based ingredients typically contain significant levels of taurine (provided it is not lost during ingredient processing). As a result, fishmeal contains taurine, usually around 0.5-0.7 percent. In contrast, plants do not contain taurine, so plant-based ingredients do not bring any taurine to the feed. As fish nutritionists improve feed formulations to increase plant-based proteins at the expense of animal-based proteins, diets contain lowered levels of taurine. This can be to the extent that for some species like Florida pompano, taurine is actually the first-limiting amino acid in soy-based diets, not methionine! Dr Salze observed that, “Before the AAFCO amended its

taurine definition, taurine had to be supplied through other animal ingredients, such as fishmeal, fish solubles, krill or squid meal, poultry-by product meal, etc. These ingredients are expensive, and increase feed costs. Also, ingredients like fishmeal rely greatly on dedicated wild fisheries. Now that the definition has been officially amended, feed can be formulated with lower levels of animal-based ingredients, because taurine can be included separately. Its inclusion is conducive to the further reduction of expensive animal protein and in turn increasing plant proteins, thereby contributing to reducing feed costs while also reducing pressures on wild fisheries.” Dr Salze highlighted that the other benefit to the American fish feed industry includes exportation to international markets. He reiterated that before the amendment of AAFCO’s definition, the United States was the only country where taurine was not approved for use in fish feed, whilst the European Union, New Zealand, China, Japan, Canada, Chile (to name a few), all have regulations in place allowing for taurine use. He concluded that, “The American producers found themselves in a difficult situation because their formulations could meet the taurine requirement through higher levels of fishmeal. In that case, the feeds were not competitive with those from other countries, since they were able to include taurine and reduce fishmeal inclusion. Buyers were aware of the importance of taurine, and were quite skeptical of un-supplemented feeds.” Alternatively, they would include taurine but then were somewhat at odds with FDA’s regulation and could be barred from accessing international markets altogether. He noted that, “Clearly, this was not a good situation, and now the gap is filled.” He clarified that, “To be clear, crystal taurine is artificially synthesised through chemical reactions. Producing taurine by extraction and purification from animal tissues is simply not feasible: the efficiencies are low, cost is very high, and there are not enough raw materials available to satisfy global demand. On the other hand, chemical synthesis is relatively simple (compared to that of some other amino acids), inexpensive, and the purity of the resulting product is very high (>98%). Very importantly, the crystal taurine has the exact same chemical structure as the taurine found in animal tissue. There is no difference whatsoever. Whoever ingests it will therefore use it just as the natural taurine would be.”

The research behind the project

Despite a great deal of information already available, Dr Salze observed that there were still some gaps that needed to be filled. So, Dr D. Allen Davis and himself (Auburn University) teamed up with four other laboratories in the country: Dr Delbert Gatlin III at Texas A&M College Station, TX, Dr Gibson Gaylord from the US Fish and Wildlife Service in Bozeman, MT, Dr Ronald Johnson from National Oceanic and Atmospheric Administration (NOAA) Fisheries in Seattle, WA, and Dr Mark Drawbridge from the Hubbs Sea World Research Institute in Carlsbad, CA. Each of the five groups were tasked with answering different questions ranging from feed manufacturing (stability of taurine,

26 | July 2017 - International Aquafeed

Jul 2017 - International Aquafeed magazine  
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