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Taurine leaching in fish feeds By Guillaume Salze1, T. Gibson Gaylord2, D. Allen Davis1 1

School of Fisheries Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL 36849

2

US Fish and Wildlife Service, Bozeman Fish Technology Center, Bozeman, MT 59715

Leaching of water soluble compounds is an issue for fish and shrimp feeds often discussed among nutritionists. Indeed, such compounds include critical nutrients and supplements such as vitamins and free amino acids.

Yet, this issue has received limited attention in terms of dedicated, quantitative studies. Taurine has been the subject of an intensive research effort, and

Photo: Guillaume Salze, Ph.D

is now widely recognized as an essential nutrient in many fish species, such as European

seabass, California yellowtail, or Japanese flounder. Traditionally supplied through animal meals such as fishmeal, taurine must be supplemented in formulations containing high levels of taurinepoor ingredients such as plantbased protein sources. As of January 2017 taurine is listed as an approved feed additive for fish feeds in the United States; thus it is only appropriate to look at this important nutrient and its retention in fish feeds.

Descriptions of symptoms of taurine deficiencies in fish have mostly been limited to depressed growth, reductions in immune response and occurrence of green liver syndrome in juveniles of some species, and development retardation in larvae. In mammals taurine is attributed many functions spanning from bile-salt formation, osmoregulation, and inhibition of oxidative stress (Huxtable, 1992). In yellowtail taurine deficiency plays a role in osmoregulation (Takagi et al., 2006), and taurine-deficient red seabream exhibit a decrease in taurine conjugated bile-salts (Matsunari et al., 2008). In Florida pompano, taurine deficiency caused significant changes in several biomarkers of liver function, including a decrease in alkaline phospha-

tase activity, accumulation of glycogen and lipid with marked vacuolation, and reduced mitochondrial function in the liver. Taken together, these findings indicate severe abnormalities in liver metabolism in fish fed taurine-deficient diets, and provide an explanation for the reduced growth, feed efficiency and liver issues commonly observed with taurine deficiency (Salze et al., 2016). Taurine is a polar molecule, and since it is a beta-amino acid and cannot form a peptide bond to form a protein, it is almost always found in free form. Taurine is therefore prone to leaching, and it is important to quantify leaching rates from practical feeds. Indeed, there are a number of factors that will affect

Aquafeed vol 9 issue 2 2017  

Aquafeed magazine is focused on advances in feed formulation and processing for aquatic species. It is the quarterly magazine of Aquafeed.co...

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