320
J. H. 9. BLAXTER AND F. a. T. HOLLIDAY
Buchmann (1940) described an increase in thyroid activity in the
herring a t spawning, when there was a high level of activity.
Studies on Brevoortia tyrannwr (Gray, 1954) showed that it had a
very high gill surface area per unit of body weight (ten times greater
than in Opeanus). Also Gray and Hall (1930) found the blood sugar
level was higher-76 mg/100 ml blood, compared with 16 mg/lOO ml
in Opsanue, and so was the iron content (41 mg/lOO ml, compared with
13.8 mg/lOO ml in Opaanue). Dawson (1933) reported a high level of
erythrocyte precursors in the blood of Brevoortia, presumably maintaining a high proportion of functional red blood cells. Vernberg and
Gray (1953) and Vernberg (1954) showed that the oxygen uptake of
the intact Brevoortia was very high, as it was dso in its excised brain
tissue (twice that of similar tissue from Opsanwr). The oxygen uptake
of isolated muscle tissue was no higher in Brevoorth than in any other
fish. It waa concluded that the nervous system imposed a higher level
of activity on the muscle by direct stimulation.
&. 8hling
1. General
A shod or school is here defined as a group of fish which are polarized or orientated in the same direction as a reaction to one another,
rather than a common reaction to an external stimulus. The fish tend
to have a regular spacing and move a t about the same speed.
The general concept of shoaling waa discussed by Breder (1959) who
referred to clupeids and quoted work on rather unusual social groupings
in Pornolobus and Alosa. He pointed out that the shoaling b b i t a of
clupeids might be to some extent correlated with the immobility of
their pectoral fins; fish with mobile and flexible pectorals, being able
to " back up ", had a form of locomotion less suited to a shoaling habit.
The importance of the silvery skin of clupeids waa also discussed. I n
some conditions this might cause flashing and help to keep the ehod
together in poor light; on other occasions the mirror effect might
reflect the colour of the surroundings and so act as a camoufiage.
Manteufel and Radakov (1960) discussed the adaptive importance of
shoaling in relation to defence, feeding, migration and spawning, and
mentioned clupeids. The high incidence of shoaling in these fkh may be
connected with their susceptibility to predation. It is well known that
they either form shod or shoal more tightly aa a result of stimuli which
may be harmful, but the survival value of shoaling is by no means
certain.
J. H. 9. BLAXTER AND F. a. T. HOLLIDAY
Buchmann (1940) described an increase in thyroid activity in the
herring a t spawning, when there was a high level of activity.
Studies on Brevoortia tyrannwr (Gray, 1954) showed that it had a
very high gill surface area per unit of body weight (ten times greater
than in Opeanus). Also Gray and Hall (1930) found the blood sugar
level was higher-76 mg/100 ml blood, compared with 16 mg/lOO ml
in Opsanue, and so was the iron content (41 mg/lOO ml, compared with
13.8 mg/lOO ml in Opaanue). Dawson (1933) reported a high level of
erythrocyte precursors in the blood of Brevoortia, presumably maintaining a high proportion of functional red blood cells. Vernberg and
Gray (1953) and Vernberg (1954) showed that the oxygen uptake of
the intact Brevoortia was very high, as it was dso in its excised brain
tissue (twice that of similar tissue from Opsanwr). The oxygen uptake
of isolated muscle tissue was no higher in Brevoorth than in any other
fish. It waa concluded that the nervous system imposed a higher level
of activity on the muscle by direct stimulation.
&. 8hling
1. General
A shod or school is here defined as a group of fish which are polarized or orientated in the same direction as a reaction to one another,
rather than a common reaction to an external stimulus. The fish tend
to have a regular spacing and move a t about the same speed.
The general concept of shoaling waa discussed by Breder (1959) who
referred to clupeids and quoted work on rather unusual social groupings
in Pornolobus and Alosa. He pointed out that the shoaling b b i t a of
clupeids might be to some extent correlated with the immobility of
their pectoral fins; fish with mobile and flexible pectorals, being able
to " back up ", had a form of locomotion less suited to a shoaling habit.
The importance of the silvery skin of clupeids waa also discussed. I n
some conditions this might cause flashing and help to keep the ehod
together in poor light; on other occasions the mirror effect might
reflect the colour of the surroundings and so act as a camoufiage.
Manteufel and Radakov (1960) discussed the adaptive importance of
shoaling in relation to defence, feeding, migration and spawning, and
mentioned clupeids. The high incidence of shoaling in these fkh may be
connected with their susceptibility to predation. It is well known that
they either form shod or shoal more tightly aa a result of stimuli which
may be harmful, but the survival value of shoaling is by no means
certain.