FISH NUTRITION
409
levels will be such as to permit a balance between lean body mass and
fat stores.
The protein sparing action of fat and carbohydrate may be
investigated by either of two types of procedure. The effect of
different dietary energy levels on growth or nitrogen retention can be
examined. Alternatively nitrogen excretion of animals receiving a low
protein diet (at or approaching maintenance levels) can be measured at
different dietary energy levels and the sparing action of energy components on protein catabolism defined.
To date only experiments of the first type appear to have been
performed on fish. Phillips et al. (1964,1965,1966) fed brook trout with
diets containing either 27% protein or 19% protein. Fat (corn oil) and
carbohydrate (dextrin, maltose) were added to the low protein diet
either separately or in combination to raise its energy level to that of the
27% protein diet.
Weight gains on the 19% protein diet (without added fat or carbohydrate) were inferior to those on the 27% protein diet. Addition of
fat to the low protein diet restored growth up to or beyond the level
obtaining on the 27% protein diet. Carbohydrates also improved
weight gains of fish receiving the low protein but they were less effective
than fats. The tissues of fish receiving the low protein-high lipid diets
contained markedly more lipid than fish receiving food with 27%
protein. Similarly Phillips and his colleagues found that addition
of maltose and dextrin to the low protein diet led to high liver glycogen
levels. Whether or not these elevated levels of body fat and liver
glycogen are detrimental to the long term health and viability of the
fish is not yet clear.
In experiments with channel catfish, Dupree (1969) used a series of
diets (36.6% protein) which contained liquid corn oil, solid corn oil
and beef tallow each at levels of 4, 8 and 16% together with dextrin
at 8 and 16%. Fish on each dietary regime were offered equal weights
of food over a 4 week period and from data on the chemical composition
of fish at the beginning and end of the experiment Dupree was able to
compare protein deposition on each regime. Both growth rate and protein
deposition were greater when the three fats were used at 8% of the dry
diet than at 4%; further increase in dietary fat to 16% resulted in
lower protein depositions. Dextrin had a greater sparing action at
8% than at 16%. I n the best diets 1 g liquid corn oil, solid corn oil
and beef tallow spared 0.38, 0.73 and 0.27 g protein respectively.
Thus solid corn oil appears more effective in protein sparing action
than the two other fats used. This is interesting and indicates that the
qualities or properties of the fat are important. Fats have not normally
409
levels will be such as to permit a balance between lean body mass and
fat stores.
The protein sparing action of fat and carbohydrate may be
investigated by either of two types of procedure. The effect of
different dietary energy levels on growth or nitrogen retention can be
examined. Alternatively nitrogen excretion of animals receiving a low
protein diet (at or approaching maintenance levels) can be measured at
different dietary energy levels and the sparing action of energy components on protein catabolism defined.
To date only experiments of the first type appear to have been
performed on fish. Phillips et al. (1964,1965,1966) fed brook trout with
diets containing either 27% protein or 19% protein. Fat (corn oil) and
carbohydrate (dextrin, maltose) were added to the low protein diet
either separately or in combination to raise its energy level to that of the
27% protein diet.
Weight gains on the 19% protein diet (without added fat or carbohydrate) were inferior to those on the 27% protein diet. Addition of
fat to the low protein diet restored growth up to or beyond the level
obtaining on the 27% protein diet. Carbohydrates also improved
weight gains of fish receiving the low protein but they were less effective
than fats. The tissues of fish receiving the low protein-high lipid diets
contained markedly more lipid than fish receiving food with 27%
protein. Similarly Phillips and his colleagues found that addition
of maltose and dextrin to the low protein diet led to high liver glycogen
levels. Whether or not these elevated levels of body fat and liver
glycogen are detrimental to the long term health and viability of the
fish is not yet clear.
In experiments with channel catfish, Dupree (1969) used a series of
diets (36.6% protein) which contained liquid corn oil, solid corn oil
and beef tallow each at levels of 4, 8 and 16% together with dextrin
at 8 and 16%. Fish on each dietary regime were offered equal weights
of food over a 4 week period and from data on the chemical composition
of fish at the beginning and end of the experiment Dupree was able to
compare protein deposition on each regime. Both growth rate and protein
deposition were greater when the three fats were used at 8% of the dry
diet than at 4%; further increase in dietary fat to 16% resulted in
lower protein depositions. Dextrin had a greater sparing action at
8% than at 16%. I n the best diets 1 g liquid corn oil, solid corn oil
and beef tallow spared 0.38, 0.73 and 0.27 g protein respectively.
Thus solid corn oil appears more effective in protein sparing action
than the two other fats used. This is interesting and indicates that the
qualities or properties of the fat are important. Fats have not normally