FISH NUTRITION
403
Protein eficiency ratio
This is defined as grams live weight gain per gram of protein consumed. The PER should be measured at several dietary levels of the
protein under test, the maximum value so obtained being accepted as
indicative of the nutritive value of the protein. PER makes no
allowance for maintenance and assumes that all food protein is used for
growth; similarly it is implicit in the method that the live weight gain
is of constant composition and this is not necessarily so ; finally PER is
probably influenced by the feeding rate employed.
Biological value
The nitrogen balance equation was mentioned earlier and the
biological value of the protein used in a nitrogen balance study is taken
as that portion of the absorbed protein which is retained by the body.
Net protein utilization
nitrogen retained by the body is measured. NPU is defined by
This is similar to biological value in that the proportion of food
B - ( B K - I d
I
where BK = body nitrogen of animals on a nitrogen-free or low
protein diet, IK = nitrogen intake of animals on a nitrogen-free or
low protein diet, B = body nitrogen of animals fed the test protein, and
I = nitrogen intake of animals fed the test protein diet. With mammals,
measurements under conditions where protein intakes are near the
maintenance level are termed " standardized " (NPU,,), and those at
higher protein levels are termed " operative ) ) (NPU,,,) (Miller and
Bender, 1955; Miller and Payne, 1961).
As yet few attempts have been made to measure the quality of
feedstuff proteins for fiah by any of these methods. Hastings (1969)
quotes results Shanks obtained with chinook salmon for PER of a
number of proteins or materials containing protein. Liver had the
highest PER of the materials tested followed by casein,-Ghmeal,
cottonseed meal and brewers' yeast in that order. Additional results
of Shanks (loc. cit.) in which both the dietary casein level and the
dextrin level were varied showed that the PER was affected by both
factors.
Figure 3 shows the variation in PER with increasing dietary protein
level for two proteins, casein and freeze dried cod muscle. This
variation is not dissimilar to that obtained in experiments with
mammals. The important point is that at different dietary protein
403
Protein eficiency ratio
This is defined as grams live weight gain per gram of protein consumed. The PER should be measured at several dietary levels of the
protein under test, the maximum value so obtained being accepted as
indicative of the nutritive value of the protein. PER makes no
allowance for maintenance and assumes that all food protein is used for
growth; similarly it is implicit in the method that the live weight gain
is of constant composition and this is not necessarily so ; finally PER is
probably influenced by the feeding rate employed.
Biological value
The nitrogen balance equation was mentioned earlier and the
biological value of the protein used in a nitrogen balance study is taken
as that portion of the absorbed protein which is retained by the body.
Net protein utilization
nitrogen retained by the body is measured. NPU is defined by
This is similar to biological value in that the proportion of food
B - ( B K - I d
I
where BK = body nitrogen of animals on a nitrogen-free or low
protein diet, IK = nitrogen intake of animals on a nitrogen-free or
low protein diet, B = body nitrogen of animals fed the test protein, and
I = nitrogen intake of animals fed the test protein diet. With mammals,
measurements under conditions where protein intakes are near the
maintenance level are termed " standardized " (NPU,,), and those at
higher protein levels are termed " operative ) ) (NPU,,,) (Miller and
Bender, 1955; Miller and Payne, 1961).
As yet few attempts have been made to measure the quality of
feedstuff proteins for fiah by any of these methods. Hastings (1969)
quotes results Shanks obtained with chinook salmon for PER of a
number of proteins or materials containing protein. Liver had the
highest PER of the materials tested followed by casein,-Ghmeal,
cottonseed meal and brewers' yeast in that order. Additional results
of Shanks (loc. cit.) in which both the dietary casein level and the
dextrin level were varied showed that the PER was affected by both
factors.
Figure 3 shows the variation in PER with increasing dietary protein
level for two proteins, casein and freeze dried cod muscle. This
variation is not dissimilar to that obtained in experiments with
mammals. The important point is that at different dietary protein