Introduction

uter feed programmes and so forth. Very little detail exists which compares one diet with another, either within one company or between companies. The only comparison a farmer can make between diets is historical - that is he can compare a new one with one he used previously by analysis of his farm records (growth rates, FCRs, etc.)

When a new diet becomes available, the benefits from it must be obvious in terms of improved growth, FCRs or product quality. If a new diet is more expensive than existing ones, there must be an accompanying decrease in the FCR if feed cost per unit of fish produced is not to go up. This is illustrated in the diagram on the screen which also shows that small changes in FCR can have a large impact on feed costs.

Effect of changes in price and FCR on fish production costs

Comparison can also be made between diets where potential FCRs and price are known.

For example, a new diet (ND) promises an FCR of 1.0 but at a price of 1100 pounds per tonne. How does this compare to an old diet (OD) at 950 pounds per tonnes giving an FCR of 1.2?

Diet ND has a feed cost per tonne of fish produced of 1100 x 1.0 = 1100 pounds, whilst cost of diet OD is 950 x 1.2 = 1140 pounds. Thus the newer, more expensive diet is actually cheaper in terms of production costs.

an komme fra manglende oksygen i mediet, eller fra manglende evne i vevet til å absorbere oksygen under forhold med lavt trykk i omgivelsene.