THE BEHAVIOUR AND PHYSIOLOGY OF HERRING AND OTHER CLUPEIDS 271
is -m°C, but these authors give a time of 49 days at 0°C. Soleim
(1942) found - 1-2°C for Atlanto-Scandian herring, Blaxter (1 956)
-1.34"C for northern North Sea herring, and Blaxter and Hempel
(1961) about 0°C for German coastal herring.
The product of temperature (using the biological zero) and time
(" day degrees ") has been used as a means of comparing stages of
development in larvae reared at different temperatures. This concept
is unsatisfactory in some ways because of the difficulty in identifying
equal stages of development from which to calculate the initial biological
zero. Also as the temperature changes, so may the relative growth of
different parts of the body. Even the time to hatching itself may vary
aa a result of environmental conditions other than temperature.
Barlow (1961) has recently suggested that the time to reach a given
developmental stage should be plotted against absolute temperature.
Ahlstrom (1943) found the Arrhenius relationship for hatching of
Sardinops caerulea to bc about 22,500. Blaxter (1966) found values
ranging from 20,800 to 9,500 in herring, with Qlo values ranging from
6.6 to 2.0.
C. Salinity tolerance and osmo-regulation of the developing egg
1. Salinity tolerance
Ford (1929) found that herring eggs could be successfully fertilized
and incubated in salinities down to 4-8%,. Kryzhanovsky (1956)
reported normal fertilization of Baltic herring eggs in salinities as high
as 25%, (normally it is 4-5%,,), although later development was abnormal. Brandhorst (1 959) reported RucceHsful spawning in th: Kiel
Canal at a salinity of 5%,. Holliday and Blaxter (1961) meawrc:d the
changes taking place in the embryonic tissues of herring rear& in
salinities from 5-55%,; they found a 100% fertilization in salinitiw
from 25-55%,, becoming 70% in 12%, and 5%,. Over 50% of the eggs
hatched in salinities from 10-45%,. McMynn and Hoar (1953) showed
that the eggs of Clupea pallasii would tolerate salinities at lea& aR low
as 6%,, and in a larger number of experiments found that t h o optimurn
salinity for development and hatching lay betwecn 11.53 and I&Y4%,,.
Galkina (1957) found in Clupea pallavii that percentage fertilizutiori
Ody fell off below salinities of 6%,.
2. Osmotic regulation
After fertilization the herring egg is almout isotonic with tho water
into which it has been shed, although it never reaches isotonicity with
is -m°C, but these authors give a time of 49 days at 0°C. Soleim
(1942) found - 1-2°C for Atlanto-Scandian herring, Blaxter (1 956)
-1.34"C for northern North Sea herring, and Blaxter and Hempel
(1961) about 0°C for German coastal herring.
The product of temperature (using the biological zero) and time
(" day degrees ") has been used as a means of comparing stages of
development in larvae reared at different temperatures. This concept
is unsatisfactory in some ways because of the difficulty in identifying
equal stages of development from which to calculate the initial biological
zero. Also as the temperature changes, so may the relative growth of
different parts of the body. Even the time to hatching itself may vary
aa a result of environmental conditions other than temperature.
Barlow (1961) has recently suggested that the time to reach a given
developmental stage should be plotted against absolute temperature.
Ahlstrom (1943) found the Arrhenius relationship for hatching of
Sardinops caerulea to bc about 22,500. Blaxter (1966) found values
ranging from 20,800 to 9,500 in herring, with Qlo values ranging from
6.6 to 2.0.
C. Salinity tolerance and osmo-regulation of the developing egg
1. Salinity tolerance
Ford (1929) found that herring eggs could be successfully fertilized
and incubated in salinities down to 4-8%,. Kryzhanovsky (1956)
reported normal fertilization of Baltic herring eggs in salinities as high
as 25%, (normally it is 4-5%,,), although later development was abnormal. Brandhorst (1 959) reported RucceHsful spawning in th: Kiel
Canal at a salinity of 5%,. Holliday and Blaxter (1961) meawrc:d the
changes taking place in the embryonic tissues of herring rear& in
salinities from 5-55%,; they found a 100% fertilization in salinitiw
from 25-55%,, becoming 70% in 12%, and 5%,. Over 50% of the eggs
hatched in salinities from 10-45%,. McMynn and Hoar (1953) showed
that the eggs of Clupea pallasii would tolerate salinities at lea& aR low
as 6%,, and in a larger number of experiments found that t h o optimurn
salinity for development and hatching lay betwecn 11.53 and I&Y4%,,.
Galkina (1957) found in Clupea pallavii that percentage fertilizutiori
Ody fell off below salinities of 6%,.
2. Osmotic regulation
After fertilization the herring egg is almout isotonic with tho water
into which it has been shed, although it never reaches isotonicity with