398
0. B. COWEY AXD J. R. SAFCGENT
A basal diet was used in which the protein component (40% of the dry
diet) comprised casein, gelatin and a crystalline amino acid mixture ;
this protein component contained only a low level of threonine. The
amino acid mixture used was so formulated that the dietary protein
component as a whole had a complement of essential amino acids
(threonine excepted) equivalent to that of whole egg protein. Diets
containing increasing levels of threonine were obtained by adding
crystalline threonine to the basal ration and removing equal quantities
of alanine plus proline.
These diets were fed to chinook salmon fingerlings for a ten week
period ; growth response curves showed a threonine requirement of
about 0.9% of the dry diet at water temperatures of both 8" and 15".
At a dietary protein level of 40% this corresponds to a threonine level
in the protein of 2.3%.
By similar methods Halver and his colleagues have now estimated
the quantitative requirements of the chinook salmon for all ten essential
amino acids (Halver et al., 1958,1959 ; Chance et al., 1964 ; Halver, 1965 ;
Klein and Halver, 1970); their findings are summarized by Mertz
(1969). Considered as a percentage of dietary protein, and bearing in
mind the higher dietary protein requirement of fish, the quantitative
essential amino acid requirements of fish are in most cases not greatly
dissimilar from those of birds and mammals.
Hastings (1969) has listed the first limiting essential amino acid in a
number of proteins and mixed protein feeds. For the great majority
of these foods the first limiting amino acid is tryptophan. This forecast
is based on the chemical score procedure (see below). In view of the
fact that the quantitative tryptophan requirement of chinook salmon
receiving a 40% protein diet will be met by a protein containing 0.5%
tryptophan (Mertz, 1969), whereas mammals and birds receiving a lower
protein diet require a protein with 1% tryptophan, the results should
be treated with a certain caution. It would be of great interest to know
(1) the quantitative tryptophan requirement in other fish and (2)
whether supplementation with tryptophan of the proteins listed by
Hastings would increase their nutritional value.
F . The use of nitrogen supplements
The distinction between essential and non-essential amino acids
implies that if the latter are truly dispensable it should be possible to
replace them in the diet with other non-specific sources of nitrogen such
as diammonium citrate, single non-essential amino acids, and
glucosamine or similar compounds.
Lardy and Feldott (1 950) showed that when diammonium citrate
0. B. COWEY AXD J. R. SAFCGENT
A basal diet was used in which the protein component (40% of the dry
diet) comprised casein, gelatin and a crystalline amino acid mixture ;
this protein component contained only a low level of threonine. The
amino acid mixture used was so formulated that the dietary protein
component as a whole had a complement of essential amino acids
(threonine excepted) equivalent to that of whole egg protein. Diets
containing increasing levels of threonine were obtained by adding
crystalline threonine to the basal ration and removing equal quantities
of alanine plus proline.
These diets were fed to chinook salmon fingerlings for a ten week
period ; growth response curves showed a threonine requirement of
about 0.9% of the dry diet at water temperatures of both 8" and 15".
At a dietary protein level of 40% this corresponds to a threonine level
in the protein of 2.3%.
By similar methods Halver and his colleagues have now estimated
the quantitative requirements of the chinook salmon for all ten essential
amino acids (Halver et al., 1958,1959 ; Chance et al., 1964 ; Halver, 1965 ;
Klein and Halver, 1970); their findings are summarized by Mertz
(1969). Considered as a percentage of dietary protein, and bearing in
mind the higher dietary protein requirement of fish, the quantitative
essential amino acid requirements of fish are in most cases not greatly
dissimilar from those of birds and mammals.
Hastings (1969) has listed the first limiting essential amino acid in a
number of proteins and mixed protein feeds. For the great majority
of these foods the first limiting amino acid is tryptophan. This forecast
is based on the chemical score procedure (see below). In view of the
fact that the quantitative tryptophan requirement of chinook salmon
receiving a 40% protein diet will be met by a protein containing 0.5%
tryptophan (Mertz, 1969), whereas mammals and birds receiving a lower
protein diet require a protein with 1% tryptophan, the results should
be treated with a certain caution. It would be of great interest to know
(1) the quantitative tryptophan requirement in other fish and (2)
whether supplementation with tryptophan of the proteins listed by
Hastings would increase their nutritional value.
F . The use of nitrogen supplements
The distinction between essential and non-essential amino acids
implies that if the latter are truly dispensable it should be possible to
replace them in the diet with other non-specific sources of nitrogen such
as diammonium citrate, single non-essential amino acids, and
glucosamine or similar compounds.
Lardy and Feldott (1 950) showed that when diammonium citrate