The Economics of feed conversion ratio (FCR), also known as feed conversion efficiency, is one of the most important principles for a fish farmer to understand. The cost of fish feed claims over half of the total budget for most fish farms. Consequently, it is very important for a fish farmer to get the optimum performing feed for the most economical price. Deciding just what is the best feed for the money can get confusing with a variety of feeds available and varying prices for each of those feeds. This can get even more confusing when one considers the varying feed conversion efficiencies of each of those feeds. This fact sheet will

examine the effect that feed conversion efficiency has on the "bottom line" feed cost per pound of fish gain.

Feed conversion efficiency or ratio is a fairly simple calculation to perform. The total weight of feed is divided by the net production (final weight minus starting weight) to obtain the feed conversion. For example, a farmer stocks 3,000 fingerlings in a pond which weigh a total of 300 pounds. The farmer feeds a total of 4,960 pounds of feed to the fish in the pond. The farmer harvests a total of 3,400 pounds of fish from the pond. The net production is 3,400 minus 300 which equals 3,100 pounds. The feed conversion is 4,960 pounds of feed divided by 3,100 pounds of net fish production which equals 1.6.

Now let's examine the true economics surrounding the cost of fish feed. Many novice fish farmers, and some experienced farmers, make the mistake of buying fish feed based solely on getting the cheapest feed available. In three years of feed studies at Langston University, the cheapest feed in the study turned out to be the most expensive, in terms of cost per pound of fish gain, in every year. Feed cost per pound of gain takes into account the feed conversion ratio by dividing the total feed cost by the net production.

The way to calculate the feed cost per pound of gain in cents is to first convert feed cost from dollars per ton to cents per pound. Since there are 2,000 pounds per ton, simply divide the feed cost in dollars per ton by 2,000 to arrive at the cost in cents per pound (you must move the decimal point two places to the right to convert from dollars to cents). Next, multiply the cost in cents per pound by the feed conversion ratio to obtain the feed cost per pound of gain.

I have calculated a number of feed costs per pound of gain for a variety of feed prices and feed conversion ratios (Table 1). This table allows for a quick comparison of the effect of feed

Table 1. Feed cost (in cents) per pound of fish gain at various feed prices and feed conversion ratios.

Feed Cost ($ / ton)

Feed 240 260 280 300 320 340 360 380

Conversion Feed Cost (¢ / pound)

Ratio 12 13 14 15 16 17 18 19

1.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0

1.2 14.4 15.6 16.8 18.0 19.2 20.4 21.6 22.8

1.4 16.8 18.2 19.6 21.0 22.4 23.8 25.2 26.6

1.6 19.2 20.8 22.4 24.0 25.6 27.2 28.8 30.4

1.8 21.6 23.4 25.2 27.0 28.8 30.6 32.4 34.2

2.0 24.0 26.0 28.0 30.0 32.0 34.0 36.0 38.0

2.2 26.4 28.6 30.8 33.0 35.2 37.4 39.6 41.8

2.4 28.8 31.2 33.6 36.0 38.4 40.8 43.2 45.6

2.6 31.2 33.8 36.4 39.0 41.6 44.2 46.8 49.4

2.8 33.6 36.4 39.2 42.0 44.8 47.6 50.4 53.2

3.0 36.0 39.0 42.0 45.0 48.0 51.0 54.0 57.0

Conversion ratio on the cost per pound of gain at a variety of feed prices. For example, should you buy a 28 % protein feed that costs $280 per ton and gets a feed conversion ratio of 2.2; a 32 % protein feed that costs $300 per ton and gets a feed conversion ratio of 1.8; or a 36 % protein feed that costs $340 per ton and gets a feed conversion ratio of 1.4? Checking Table 1 we find that the $280 per ton feed costs 30.8 cents per pound of gain; the $300 per ton feed costs 27.0 cents per pound of gain; and the $340 per ton feed costs 23.8 cents per pound of gain. In this example, it would obviously be more economical to purchase the most expensive 36 % protein fish food.

A fish farmer must keep accurate records in order to calculate feed conversion ratios which will allow the farmer to make an informed feed purchasing decision. A farmer may have to conduct a feed trial with potential feeds in order to establish the feed conversion ratio since this important information is not generally available. Other factors also enter into the feed purchasing decision. The higher protein feeds generally result in faster growth rates which translates into a quicker, more economical turnover of fish stocks. Also, a feed that gets a much better (lower) feed conversion puts more feed in the fish and less waste into the water to degrade water quality. The most important point to remember is that the combination of cost and feed conversion ratio determines the most economical choice of feed.