Salmon AA Recommendations Deficient in Lysine

Norwegian Research shows salmon require 30% more lysine than previously thought
March 20, 2007

Salmon AA Recommendations Deficient in Lysine

The National Institute of Nutrition and Seafood Research (NIFES) has developed a new feed which shows that farmed salmon need 30% more of the essential amino acid lysine than previously thought. Salmon which do not get enough lysine are fattier than salmon which receive enough lysine.

Fishmeal use to be the main source of proteins in salmon feed. Today, however, more than 50% of this is often replaced with plant proteins because of the great strain on traditional marine raw materials.

“Fishmeal contains an optimal balance of the essential amino acids, while a plant protein raw material does not. A fish feed with high levels of plant proteins may result in a fish feed that does not contain enough essential amino acids. This may influence fish health and growth”, says Marit Espe, researcher in the Aquaculture Nutrition Group at NIFES.

“NIFES has developed a feed that can be used to study whether fish feed with high levels of plant protein cover the salmon’s need for essential amino acids.”

The test feed
A suitable test feed has to contain low levels of fishmeal and high levels of plant proteins to allow for a low lysine containing feed. The feed must appeal to the fish’s appetite, and the fish must grow well on the test feed in order to enable a comparison between this fish and fish given a feed made from marine raw materials.

“In a test, Atlantic salmon in seawater with a starting weight of 300 grams were fed six different feeds. The fish meal was totally or partially replaced with plant proteins (wheat, gluten and corn). The feed with 5 % fishmeal, 5 % hydrolysed fish protein and 3 % squid hydrolysate turned out to be well suited for studying amino acid metabolism in salmon”, says Espe.

Salmon need more lysine
The test feed had an amino acid profile similar to the control feed, but with the possibility of varying the levels of a desired amino acids. Farmed salmon weighing 600 grams were fed the test feed, which in this case contained from very low to very high levels of the essential amino acid lysine.

“The results showed that salmon that received inadequate levels of the essential amino acid lysine deposited less proteins and were fattier than salmon receiving enough lysine. The weights of fish fed on two different feds were similar”, says Espe.

 “The test feed showed that Atlantic salmon weighing 600-1100 grams actually need 30 % more lysine than what is recommended today”, she says in closing.

Today’s recommendations comply with NRC 1993. The test feed can also be used to study farmed salmon’s need for other essential amino acids, when the feed composition is changed to include a large proportion of plant proteins.

Ewos Innovation and Degussa were partners in this study.

More information from Marit Espe, Scientist with the Programme for Aquaculture Nutrition Research at NIFES: