FISH NUTRITION
413
rapid utilization of carbohydrate as a source of energy is indicated. In
overall terms this may be described by the following equation :
C,H,,O, + 6 0 , --+ 6 CO, + 6 H,O + 673 kcal
dioxide
A ration poor in carbohydrate entails the use of either lipid or protein to
provide necessary calories. The former may involve some risk of ketosis
while the latter is expensive. From the economic viewpoint it appears
desirable to provide fish which are being farmed with as much dietary
carbohydrate as they are able to utilize without incurring deleterious
effects.
Carbohydrates include sugars, starches and celluloses, and are
composed very largely of carbon, hydrogen and oxygen with the latter
two elements present in essentially the same ratio as in water.
Monosaccharides are the simplest naturally occurring units of carbohydrates, but only the hexoses (glucose, fructose, galactose, mannose)
are of nutritional significance. Glucose and fructose occur in nature as
free sugars, and other hexoses occur mainly as units of disaccharide5
(compounds such as sucrose, maltose and lactose which yield two
monosaccharides on hydrolysis).
Polysaccharides are large molecules of varying size. Cellulose, the
most abundant of naturally occurring organic compounds, is composed
of many repeating units of the disaccharide cellobiose in which two
glucose residues are joined in j? 1+4 linkage. The repeating disaccharide unit of starches is maltose in which two glucose residues are
joined in a 1 -+4 linkage. Native starches are a mixture of amylose and
amylopectin the former consisting of long unbranched chains and the
latter of branched chains in which one terminal residue occurs in every
twenty-five or so glucose residues. Glycogen can be regarded as the
animal equivalent of starch ; it is a branched chain polysaccharide
occurring in liver and muscle.
glucose oxygen
carbon water
A . Utilization
The assimilation of starches depends on the possession by the fish
of amylases which will degrade the complex molecule to readily
assimilable glucose. Amylases are of two types a- and /?-, the former
attacks a 1+4 glycosidic bonds (other than that in the disaccharide
maltose) in random fashion giving rise from amylose to a mixture of
glucose and maltose. /?-amylase removes successive maltose units
from the non-reducing end of amylose.
Neither enzyme will attack the a 1 -+6 bonds occurring at the branch
413
rapid utilization of carbohydrate as a source of energy is indicated. In
overall terms this may be described by the following equation :
C,H,,O, + 6 0 , --+ 6 CO, + 6 H,O + 673 kcal
dioxide
A ration poor in carbohydrate entails the use of either lipid or protein to
provide necessary calories. The former may involve some risk of ketosis
while the latter is expensive. From the economic viewpoint it appears
desirable to provide fish which are being farmed with as much dietary
carbohydrate as they are able to utilize without incurring deleterious
effects.
Carbohydrates include sugars, starches and celluloses, and are
composed very largely of carbon, hydrogen and oxygen with the latter
two elements present in essentially the same ratio as in water.
Monosaccharides are the simplest naturally occurring units of carbohydrates, but only the hexoses (glucose, fructose, galactose, mannose)
are of nutritional significance. Glucose and fructose occur in nature as
free sugars, and other hexoses occur mainly as units of disaccharide5
(compounds such as sucrose, maltose and lactose which yield two
monosaccharides on hydrolysis).
Polysaccharides are large molecules of varying size. Cellulose, the
most abundant of naturally occurring organic compounds, is composed
of many repeating units of the disaccharide cellobiose in which two
glucose residues are joined in j? 1+4 linkage. The repeating disaccharide unit of starches is maltose in which two glucose residues are
joined in a 1 -+4 linkage. Native starches are a mixture of amylose and
amylopectin the former consisting of long unbranched chains and the
latter of branched chains in which one terminal residue occurs in every
twenty-five or so glucose residues. Glycogen can be regarded as the
animal equivalent of starch ; it is a branched chain polysaccharide
occurring in liver and muscle.
glucose oxygen
carbon water
A . Utilization
The assimilation of starches depends on the possession by the fish
of amylases which will degrade the complex molecule to readily
assimilable glucose. Amylases are of two types a- and /?-, the former
attacks a 1+4 glycosidic bonds (other than that in the disaccharide
maltose) in random fashion giving rise from amylose to a mixture of
glucose and maltose. /?-amylase removes successive maltose units
from the non-reducing end of amylose.
Neither enzyme will attack the a 1 -+6 bonds occurring at the branch