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Too much food?

by the Fish Site Editor
07 February 2007, at 12:00am

NORWAY - Research indicates that farmed cod receive too much food. A study now in progress at Fiskeriforskning shows that cod grow just as well even when the amount of feed is halved.

Are farmed cod getting too much food?

Measurements of the fish from hatching to three months old show that it is possible to halve the feed manufacturers' recommended amount of feed and still achieve equally good growth.

In the test, cod will be followed for two years until they are ready for slaughter. If the amount of feed can be halved during the entire period, this will mean huge savings and improved profits for the farmers.

Not utilising the food

The background for the research is studies of adult and slaughter-ready farmed cod. Cod normally store fat in the liver, but images taken using a microscope show that farmed cod also store fat in the muscles.

"When fat is stored in the muscle, this shows that the farmed cod is unable to utilise all the food it gets", says Senior Scientist Gunn Berit Olsson at Fiskeriforskning.

"We have also done studies that show changes in proteins and enzymes that are important for energy utilisation in the farmed cod's cells. When these do not function as they should, the fish cannot utilise food and energy in a normal way."

"The changes in the cells could mean that the farmed cod is getting too much food. Another possibility is that the feed contains too many minerals."

Four diets

The scientists are also studying the effects of mineral additives, which are common in fish feed to ensure normal growth and development.

The fish in the study are divided into four groups on different diets.

One group gets ordinary commercial feed, another gets feed without mineral additives, a third group gets feed with mineral additives but minus zinc and copper, while the last group gets half the amount of feed, which is without minerals.

So far, nothing has indicated that mineral additives provide any extra benefits.

"Cod grow equally well without mineral additives. Seawater has a natural content of minerals and perhaps this is enough to cover the cod's mineral requirements", says Senior Scientist Marie Cooper.

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