414
(1. B. COWEY AND J. R. SARGENT
points in amylopecten nor will they attack the / 3 1-4 bonds in
cellulose. From amylopecten, a-amylase will yield a mixture of branched
and unbranched oligosaccharides (of up to about ten glucose
residues); /3-amylase will yield maltose units until a branch point is
reached when reaction ceases.
Studies on extracts from the gastrointestinal tract (Fish, 1960;
Kitamikado and Tachino ,1960 ; Ushiyamaet aE., 1965) have revealed the
presence in fish of a-amylase. Enzymes which hydrolyse disaccharides
(a-glucosidase, /I-glucosidase, j3-galactosidase) are also present in various
organs but their activity relative to that of a-amylase is very low
(Nagayama and Saito, 1968). It w i l l be clear from the foregoing discussion that the cleavage of starch and its assimilation will depend
on the relative amounts of amylose and of amylopecten present in it.
The studies on fish gastrointestinal enzymes have demonstrated that
herbivorous species have very much more amylase activity than do
carnivores. Most of these studies were made on crude extracts which
presumably contained active proteases (especially the extracts of
carnivorous fish). As amylase is a protein it would clearly be open to
attack and inactivation by these proteases present in the extract.
Thus estimates of fish gastro-intestinal amylase activity made on such
extracts are, at best, approximations of the amylolytic activity actually
present.
The ability of rainbow trout to assimilate different carbohydrates
was examined by Singh and Nose (1967) using the chromic oxide inert
indicator method mentioned earlier. Glucose and the disaccharides
sucrose and lactose were more or less completely assimilated in the
dietary range used, 20-60% (dry diet). The authors assume hydrolysis
of the disaccharides prior to assimilation, but whether this hydrolysis
occurs in the intestinal mucosa or the lumen of the intestine is not yet
clear ; only monosaccharides have been reported in the bloodstream.
The assimilation of both potato a-starch and of dextrin (a partially
acid-hydrolysed starch) decreased as their level in the diet was increased.
At a dietary level of 20%, potato starch and dextrin were 69% and 77%
assimilated respectively, but only 26% of potato starch and 45% of
dextrin were assimilated when their dietary levels were 60%. The
pattern of assimilation of dextrin by plaice is similar (Table VIII) but
other carbohydrates have yet to be tested. Starch is poorly digested
by yellowtail (Kitamikado et al., 1965).
Buhler and Halver (1961) studied the utilization of different carbohydrates by chinook salmon. A series of diets of constant protein
content (37.5%) but in which increasing amounts of dextrin (0-48%)
were substituted for the inert a-cellulose were fed to fingerlings. Weight
(1. B. COWEY AND J. R. SARGENT
points in amylopecten nor will they attack the / 3 1-4 bonds in
cellulose. From amylopecten, a-amylase will yield a mixture of branched
and unbranched oligosaccharides (of up to about ten glucose
residues); /3-amylase will yield maltose units until a branch point is
reached when reaction ceases.
Studies on extracts from the gastrointestinal tract (Fish, 1960;
Kitamikado and Tachino ,1960 ; Ushiyamaet aE., 1965) have revealed the
presence in fish of a-amylase. Enzymes which hydrolyse disaccharides
(a-glucosidase, /I-glucosidase, j3-galactosidase) are also present in various
organs but their activity relative to that of a-amylase is very low
(Nagayama and Saito, 1968). It w i l l be clear from the foregoing discussion that the cleavage of starch and its assimilation will depend
on the relative amounts of amylose and of amylopecten present in it.
The studies on fish gastrointestinal enzymes have demonstrated that
herbivorous species have very much more amylase activity than do
carnivores. Most of these studies were made on crude extracts which
presumably contained active proteases (especially the extracts of
carnivorous fish). As amylase is a protein it would clearly be open to
attack and inactivation by these proteases present in the extract.
Thus estimates of fish gastro-intestinal amylase activity made on such
extracts are, at best, approximations of the amylolytic activity actually
present.
The ability of rainbow trout to assimilate different carbohydrates
was examined by Singh and Nose (1967) using the chromic oxide inert
indicator method mentioned earlier. Glucose and the disaccharides
sucrose and lactose were more or less completely assimilated in the
dietary range used, 20-60% (dry diet). The authors assume hydrolysis
of the disaccharides prior to assimilation, but whether this hydrolysis
occurs in the intestinal mucosa or the lumen of the intestine is not yet
clear ; only monosaccharides have been reported in the bloodstream.
The assimilation of both potato a-starch and of dextrin (a partially
acid-hydrolysed starch) decreased as their level in the diet was increased.
At a dietary level of 20%, potato starch and dextrin were 69% and 77%
assimilated respectively, but only 26% of potato starch and 45% of
dextrin were assimilated when their dietary levels were 60%. The
pattern of assimilation of dextrin by plaice is similar (Table VIII) but
other carbohydrates have yet to be tested. Starch is poorly digested
by yellowtail (Kitamikado et al., 1965).
Buhler and Halver (1961) studied the utilization of different carbohydrates by chinook salmon. A series of diets of constant protein
content (37.5%) but in which increasing amounts of dextrin (0-48%)
were substituted for the inert a-cellulose were fed to fingerlings. Weight