May 30, 2008
 

Farmed salmon can synthesize taurine needs with the right feed mix 

Research at the Norwegian National Institute of Nutrition and Seafood Research (NIFES) has shown that the farmed salmon's requirement for taurine is met when the feed contains sufficient amount of the precursor amino acids.

Fishmeal contains high levels of the essential amino acid taurine. However, due to limited access of fishmeal traditionally used in fish feed, grow-out feed for Atlantic salmon usually contains up to 50 percent plant protein.

As taurine is absent in plant proteins, the question arises whether salmon fed on plant proteins are supplied with sufficient amounts of taurine.

Research at NIFES shows that salmon is capable of synthesizing taurine from such diets when levels of the amino acids methionine and cystein are sufficient.

Taurine plays an important role in human vision and brain development, as well as in absorption of lipids from the gastrointestinal tract. Taurine is synthesized from amino acids methionine and cysteine, which involves an enzyme.

It has been assumed that taurine also is an essential amino acid for salmon fry in fresh water and for grow-out salmon in seawater. Taurine is a beta- amino acid of which, unlike the alpha amino acids, is not incorporated into proteins.

In a feed trial, grow-out salmon weighing 0.5 kilogrammes were fed feed which contained a high level of plant protein at five inclusion levels of the amino acid methionine. Besides different levels of methionine, nutrient composition was equal in all diets. Based on the metabolites from methionine degradation in the liver, which synthesizes and degrades proteins, the salmon's requirement for this amino acid was determined.

"When the requirement for methionine was met, methionine in excess was converted into taurine," says Marit Espe at the Aquaculture Nutrition Research Programme at NIFES.

"The higher the levels of methionine in the diet, the higher the levels of taurine was observed in the salmon's liver.

"This suggests that salmon fed diets with low taurine as plant protein based diets has the ability to produce sufficient amounts of taurine assuming that it is supplied with enough methionine. If the feed also contains cysteine, the need for methionine is lower than previously thought," she continued.

Recommended levels of methionine for Atlantic salmon range from 2.2 to 2.3 grammes of methionine/100gramme protein in the grow-out feed.