392
U. B. COWEY AND J. R. SARGENT
fish in a 24 h period and then used specific methods to identify and
measure the component substances. He found that in these three fish,
urea and ammonia made up the bulk of the excreted nitrogen (75%90%) and that in starry flounder, sculpin and blue sea perch respectively ammonia made up 84%, 63% and 48% of the total. The
variation here is such that it seems highly desirable that the relative
proportions of urea and ammonia in the excreta of marine fish, which
are the subjects of farming projects, be determined so that the
calorific value of dietary protein may be properly assessed.
A further complicating factor in evaluating the calorific value of
protein is the extent to which protein exerts a specific dynamic action
in fish. If this effect does occur, and at the levels of dietary protein with
which we are dealing it seems distinctly possible, then some reduction
in the calorific value allocated to protein would have to be introduced
to compensate for the elevation in metabolic rate.
C . Essential amino acid requirements
Experiments with mammals in the early years of the present
century showed that certain proteins when fed as single sources of
protein were incapable of supporting growth. When such proteins
were supplemented with one or more amino acids growth was sustained,
thereby indicating the essential dietary need for particular amino acids.
Great advances followed from about I930 onwards, very largely
because of a classic series of studies on the part of W. C. Rose and his
colleagues (see, for example, Rose, 1938). Ultimately, Rose obtained
good growth of rats on a wholly defined diet in which all the nitrogen
(a trivial amount present in some vitamins apart) was supplied by
crystalline amino acids of extreme purity. By successively removing
and later replacing amino acids from this diet Rose was able to
distinguish between those amino acids essential for growth in rats
and those not essential, i.e. that the animal itself can biosynthesize
at a rate sufficient for normal growth. The essential amino acids are
listed in Fig. 1, which depicts their structural relations.
Establishment of the essential amino acid requirements of fish was
clearly a pre-requisite to further study of their protein nutrition.
The use of defined or partially defined diets with fish presented
particular problems because of their aquatic habit. Much credit is
therefore due to J. E. Halver who first designed and used a successful
amino acid test diet for fish (Halver, 1957b). This diet has provided
an impetus for the vital trend toward defined diets in fish nutrition and
many subsequent studies owe their inspiration to this pioneer.
By use of such a diet containing 18 L-amino acids as the only source
U. B. COWEY AND J. R. SARGENT
fish in a 24 h period and then used specific methods to identify and
measure the component substances. He found that in these three fish,
urea and ammonia made up the bulk of the excreted nitrogen (75%90%) and that in starry flounder, sculpin and blue sea perch respectively ammonia made up 84%, 63% and 48% of the total. The
variation here is such that it seems highly desirable that the relative
proportions of urea and ammonia in the excreta of marine fish, which
are the subjects of farming projects, be determined so that the
calorific value of dietary protein may be properly assessed.
A further complicating factor in evaluating the calorific value of
protein is the extent to which protein exerts a specific dynamic action
in fish. If this effect does occur, and at the levels of dietary protein with
which we are dealing it seems distinctly possible, then some reduction
in the calorific value allocated to protein would have to be introduced
to compensate for the elevation in metabolic rate.
C . Essential amino acid requirements
Experiments with mammals in the early years of the present
century showed that certain proteins when fed as single sources of
protein were incapable of supporting growth. When such proteins
were supplemented with one or more amino acids growth was sustained,
thereby indicating the essential dietary need for particular amino acids.
Great advances followed from about I930 onwards, very largely
because of a classic series of studies on the part of W. C. Rose and his
colleagues (see, for example, Rose, 1938). Ultimately, Rose obtained
good growth of rats on a wholly defined diet in which all the nitrogen
(a trivial amount present in some vitamins apart) was supplied by
crystalline amino acids of extreme purity. By successively removing
and later replacing amino acids from this diet Rose was able to
distinguish between those amino acids essential for growth in rats
and those not essential, i.e. that the animal itself can biosynthesize
at a rate sufficient for normal growth. The essential amino acids are
listed in Fig. 1, which depicts their structural relations.
Establishment of the essential amino acid requirements of fish was
clearly a pre-requisite to further study of their protein nutrition.
The use of defined or partially defined diets with fish presented
particular problems because of their aquatic habit. Much credit is
therefore due to J. E. Halver who first designed and used a successful
amino acid test diet for fish (Halver, 1957b). This diet has provided
an impetus for the vital trend toward defined diets in fish nutrition and
many subsequent studies owe their inspiration to this pioneer.
By use of such a diet containing 18 L-amino acids as the only source