I am using a juvenile fish for my experiment. My FCR seems to be lower than 1. I heard once in an International conference that it is not possible to get less than 1 FCR.
It is possible for a reason that if the animal is cultured in a quite different salinity regime, its excretory system will be subjected to substantial strain, leading to usage of high energy from feed, giving a low FCR.
It is possible in open fish farm.
In your case it may be due to improper water change which favorabl micrfouna
fcr will be low and under 1 while fish is small but only for some limited time and small period of farming. it is not possible to have fcr under 1 if you want to have fish for harvest
Logically and practically it is possible. But the idea will work out under low stocking density condition and not under intensive farming conditions.
HI Dr. Plasus,
If you look at it, the FCR equation is designed for production and profitability index, purpose of rearing aquatic animals. This is a crude and practical way of evaluating the the feed intake and its influence on growth.
Careful analysis of the equation, however ( FCR= feed intake(dry feed)/ gain in weight (wet weight) reveals that the equation appears to be disconnected. My point is , that weight gain is measured as direct wet weight, while feed intake is measures as dry feed eaten. So an FCR of 1 or less than 1 is feasible and is real, since the weight gain being measured is in terms of wet weight . THe additional weight gain could be water that accumulates in the wet tissues.
I do agree that feed conversion to tissue biomass (Dry to dry basis, a value of 1 is impossible , but not FCR) . NUtrient retention of 1 is impossible since the equation requires a dry to dry basis but FCR is not, since it is measured in a wet to dry basis.
Example : Feed intake is 2 kg (dry feed), weight gain is 2 kg wet basis, so FCR is 1. However careful analysis suggests that if the wet animal has a water content of 70% so the wet gain is just 0.6 Kg so the real Nutrient utilization in dry to dry basis is 2kg/ 0.6kg = 2.5 which the feed efficiency in dry basis is only 40%. Meaning if you feed the fish with 10 tons of feed only 4 tons is assimilated as growth but the 6 tons goes to the environment as wastes.
My point is FCR is a crude measure of feed utilization and an FCR of 1 if analyzed on a dry matter basis it would translate to only 40% feed utilization efficiency. meaning 60% of your feed goes to the environment as wastes.
So I am always recommending not to uses FCR in estimating waste production of cultured fish. It should be nutrient retention, that is quantified on a dry matter basis.
Hope this is helpful and clarifies the Less than 1 FCR issues.
Hi Dr. Rex, thank you for your very informative answer. I was actually asked by the judges during the conference if my computation was correct. I knew it was correct but was not really able to give a concrete answer to why it was less than 1. Anyway, thank you very much!
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