THE BEHAVIOER" AND PHYSIOLOGY OF HERRING AND OTHER CLUPEIDS 299
this acidity was neutralized by the bile in the intestine. More peptic
activity was found in the full stomach than in the empty, or partly
full one. The pH optimum for pepsin was between 2.5 and 2.85. Its
activity increased with rise in temperature (Ql0 = 1.5). The level of
trypsin in the pyloric caecae was highest in herring with full stomachs.
Calcium salts present in the food increased the activity of trypsin.
The pH optimum lay between 8.5 and 9.5, the Qlo being 1.5. The
lipase of the pyloric caecae was rendered more active by the bile.
4. EfJect of enzymes on food
Battle ( 1935) reported that live euphausiids, Meganyctiphanes, were
killed in 3-4 min, and the copepods, Calunus and Temora, in 30 sec, by
the action of the stomach secretions. Breakdown of the food started in
the caecal and pyloric regions of the stomach, while in the pyloric
caecae the food was in the form of an oily chyme, mixed with mucus.
The bacteria in the gut might aid in digestion. Chitin from the food,
and a large proportion of the oil, passed out with the faeces, often
causing an oily film on the water in which herring were feeding.
5. Time for digestion
The length of time that the food stays in the gut depends on the
temperature (Fig. 6) and on the feeding history of the fish. Blaxter and
Holliday (1958) showed that food took longest to pass through the gut
when fish were starved before andfor after the test feed. Battle et al.
(1936) suggested that small herring retained food in the gut longer than
large herring.
D. Fat storage and metabolism
1. Cyclical changes
The clupeids are seasonal feeders, building up large stores of fat to
sustain them when food is in poor supply. The overall changes in body
fat of the herring in relation to feeding, age, size, race and maturity
stage have been extensively studied (for bibliography see Wood, 1958).
Similar studies have been made on Sardinu pilchardus (Hickling, 1945)
and Sprattw sprattw (Liihmann, 1952). A good deal of individual
variation exists, but it is the intensity of feeding that is the overriding
factor in determining the fat reserves. The spring and autumn plankton
peaks provide potentially rich feeding and whether the fish make use
of this food depends to a large extent on the condition of the gonads,
fish with well developed gonads feeding only to a very small extent.
Thus the autumn-spawning herring feed and lay down fat reserves in
this acidity was neutralized by the bile in the intestine. More peptic
activity was found in the full stomach than in the empty, or partly
full one. The pH optimum for pepsin was between 2.5 and 2.85. Its
activity increased with rise in temperature (Ql0 = 1.5). The level of
trypsin in the pyloric caecae was highest in herring with full stomachs.
Calcium salts present in the food increased the activity of trypsin.
The pH optimum lay between 8.5 and 9.5, the Qlo being 1.5. The
lipase of the pyloric caecae was rendered more active by the bile.
4. EfJect of enzymes on food
Battle ( 1935) reported that live euphausiids, Meganyctiphanes, were
killed in 3-4 min, and the copepods, Calunus and Temora, in 30 sec, by
the action of the stomach secretions. Breakdown of the food started in
the caecal and pyloric regions of the stomach, while in the pyloric
caecae the food was in the form of an oily chyme, mixed with mucus.
The bacteria in the gut might aid in digestion. Chitin from the food,
and a large proportion of the oil, passed out with the faeces, often
causing an oily film on the water in which herring were feeding.
5. Time for digestion
The length of time that the food stays in the gut depends on the
temperature (Fig. 6) and on the feeding history of the fish. Blaxter and
Holliday (1958) showed that food took longest to pass through the gut
when fish were starved before andfor after the test feed. Battle et al.
(1936) suggested that small herring retained food in the gut longer than
large herring.
D. Fat storage and metabolism
1. Cyclical changes
The clupeids are seasonal feeders, building up large stores of fat to
sustain them when food is in poor supply. The overall changes in body
fat of the herring in relation to feeding, age, size, race and maturity
stage have been extensively studied (for bibliography see Wood, 1958).
Similar studies have been made on Sardinu pilchardus (Hickling, 1945)
and Sprattw sprattw (Liihmann, 1952). A good deal of individual
variation exists, but it is the intensity of feeding that is the overriding
factor in determining the fat reserves. The spring and autumn plankton
peaks provide potentially rich feeding and whether the fish make use
of this food depends to a large extent on the condition of the gonads,
fish with well developed gonads feeding only to a very small extent.
Thus the autumn-spawning herring feed and lay down fat reserves in