News 264 views last update:6 Aug 2012

Fish vegies need more lysine

Farmed salmon need 30% more lysine than previously thought and salmon which do not get enough lysine have more fat than salmon which receive adequate lysine, says NIFES, the Norwegian National Institute of Nutrition and Seafood Research.

In response to the trend to replace more than 50% of the fishmeal in salmon diets with plant proteins, NIFES has developed a feed that can be used to study whether feed with high levels of plant protein cover the salmon's need for essential amino acids.

"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.

Atlantic salmon in seawater with a starting weight of 300 grams was 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% hydrolyzed fish protein and 3% squid hydrolysate was best suited for studying amino acid metabolism in salmon.

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 acid.

Low lysine, fat fish
Farmed salmon weighing 600 grams were fed the test feed, which in this case contained from very low to very high levels of lysine. "The results showed that salmon which received inadequate levels of lysine deposited less protein and were fattier than salmon receiving enough lysine. The weights of fish fed on two different feeds 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."

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.

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