Taurine

Product introduction

Taurine, 2-aminoethanesulfonic acid, is an organic acid that has a variety of functions as a constituent of bile and in osmoregulation,cell membrane stabilization, antioxidation and early development of visual, muscular and neural systems. Taurine is not an amino acid, since it lacks a carboxyl group and has not been found within any known protein structure, but is often classified as an amino acid.

Taurine exists naturally in animals, including oysters, mussels and fish, but is not found in most plants. Consequently, supplementation of taurine in diets for select species of fish containing high levels of alternative proteins may be necessary. As a chemical reagent for food additives, taurine is added to cat food, chicken feed, energy drinks, infant formula, dietary supplements, cosmetics, inert ingredients in pesticides and pharmaceuticals.

As marine ingredient levels are reduced in aquafeed,supplementation with low levels of taurine may be required to optimize production. Taurine may not only improve growth and performance, but also is required to reduce nutritional diseases such as green liver disease and low hematocrit levels in some fish. Taurine is authorized for fish feed in all species in the European Union and China, but not the United States.

There is also growing interest in using taurine in aquaculture diets. In the European Union and China, taurine is authorized for fish feed in all species. However, in the United States, current regulations would most likely need modification, as they do not list fish.

There is increasing interest in the replacement of fishmeal and other marine ingredients in aquafeeds with alternative proteins. Plant proteins such as soybean meal have received considerable attention, but they contain low or undetectable levels of taurine. In fact, many terrestrial animal meals do not contain adequate levels of taurine, and as a result of processing methods, taurine content varies considerably.

Consequently, the use of such alternative protein sources in aquatic feeds may require supplementation with taurine. In a feeding trial conducted at Auburn University with Florida pompano,Trachinotus carolinus, the supplementation of taurine in diets containing plant proteins in combination with about 14% meat and bone meal with blood or 14% poultry by-product meal resulted in enhanced pompano growth and survival.

The response was higher in the former diet, as it contained a lower basal level of taurine. This is only one example of many studies showing that taurine may be an essential nutrient for some fish species. 

Fish Requirement

Increasing evidence indicates some marine fish have a conditional requirement for taurine. The taurine content in many
of the protein sources and attractants used in marine fish diets may be a primary contributor to the positive responses to these ingredients.

In fish, the ability to synthesize taurine varies among species due to differences in the activity of key enzymes on the pathway of taurine biosynthesis and during ontogenesis. Research has been conducted on several species of larval and juvenile fish, including Japanese flounders, European seabass, red sea bream,yellowtail, cobia, Florida pompano and sole, with results suggesting that taurine may be essential for younger fish. Freshwater species such as rainbow trout and tilapia have positively responded to taurine, whereas common carp and Atlantic salmon do not show a response.

A compilation of the utilization of taurine in diets for several marine and freshwater species is presented in Table 1. The table's comparison among species leads to the conclusions that response to dietary taurine seems to be species-specific and varies among species and growth stages. These results indicate that the dietary supplementation of taurine may be necessary when taurine levels are lower than a minimum requirement.

Supplemental taurine may not only improve growth and performance, but also is required to reduce nutritional diseases
such as green liver disease and low hematocrit levels, which seem to be characteristic of a deficiency. 

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