282
J. H. 8. BLAXTER AND F. 0 . T. HOLLIDAY
were the later hatching 1ama.e at normal temperatures. She suggested
that a wide variability in larval viability permitted the stronger larvae
to survive when food was poor. Anokhina (1961), working on Baltic
herring, found in a restricted sample that the variability of egg size
was greater from parents with low fat content, suggesting that where
fat was low, food was poor, and at least the larger eggs would have a
chance of producing larvae which would survive. However, this result
would bear further examination, particularly in relation to fat utilization and the different stages of maturation when yolk may be laid
down. Ivlev (1966) measured the loss of weight in starving larvae of
Caspiatosa volgemis. After 20 days 64% survived, the average weight
loss being 18.1% ; after 30 days when only 7% were left alive, the
weight loss was 22.1%.
Laboratory studies of larval fish survival in general were referred to
by Morris (1966) and Farris (1960). The occurrence of high mortalities
in rearing experiments may not necessarily be paralleled in the sea. In
rearing experiments on herring, the following causes of mortality have
been reported-gas disease (bubbles of gas in the intestine) by Kotthaus
(1939), Schach (1939), Soleim (1 942), Dannevig (1 948), Dannevig and
Dannevig (1960), Dannevig and Hansen (1962) and Blaxter and
Hempel (1961); attack by hypotrichous ciliates by Kotthaus (1939);
becoming caught or out by artificial glass-wool substrata by Schach
(1939); attack by Lentospora cerebralis (?), and the use of unsuitable
food by Dannevig and Hansen (1962); being sucked against the water
outflow by Schach (1939) ; and capture by Coryne and blockage of the
gut by Blaxter (1962).
Blaxter and Hempel (1961) found two phases of mortality in herring
larvae during rearing experiments, the firut after yolk HUC ahwrption
and the second at 18-20 mm. Both phases occurred denpitr! an ehundant,
though not necessarily suitable, food upp ply. Many fttiluyw f ~ , rwr
clupeid larvae after absorption of the yolk munt haw: hx:n dnr: t r ,
unsatisfactory food, but from cams where 8omc larvw: havc: AIJrviv(!d,
i t would appear that the ability to Burvivo varicH widely from larva to
larva, even from the samc parente. The second phaso of mortality
mentioned above might have bcen due to the imperfect development of
a particular organ system.
At present, proof of the existence of critical periodn for Burviva1 of
larvae in the sea must await the development of a sufficiently continuous and comprehensive sampling programme on a larval population.
Clearly, however, the survival of a brood must depend on a number of
factors, two of which are feeding, which has already been discussed, and
predation.
J. H. 8. BLAXTER AND F. 0 . T. HOLLIDAY
were the later hatching 1ama.e at normal temperatures. She suggested
that a wide variability in larval viability permitted the stronger larvae
to survive when food was poor. Anokhina (1961), working on Baltic
herring, found in a restricted sample that the variability of egg size
was greater from parents with low fat content, suggesting that where
fat was low, food was poor, and at least the larger eggs would have a
chance of producing larvae which would survive. However, this result
would bear further examination, particularly in relation to fat utilization and the different stages of maturation when yolk may be laid
down. Ivlev (1966) measured the loss of weight in starving larvae of
Caspiatosa volgemis. After 20 days 64% survived, the average weight
loss being 18.1% ; after 30 days when only 7% were left alive, the
weight loss was 22.1%.
Laboratory studies of larval fish survival in general were referred to
by Morris (1966) and Farris (1960). The occurrence of high mortalities
in rearing experiments may not necessarily be paralleled in the sea. In
rearing experiments on herring, the following causes of mortality have
been reported-gas disease (bubbles of gas in the intestine) by Kotthaus
(1939), Schach (1939), Soleim (1 942), Dannevig (1 948), Dannevig and
Dannevig (1960), Dannevig and Hansen (1962) and Blaxter and
Hempel (1961); attack by hypotrichous ciliates by Kotthaus (1939);
becoming caught or out by artificial glass-wool substrata by Schach
(1939); attack by Lentospora cerebralis (?), and the use of unsuitable
food by Dannevig and Hansen (1962); being sucked against the water
outflow by Schach (1939) ; and capture by Coryne and blockage of the
gut by Blaxter (1962).
Blaxter and Hempel (1961) found two phases of mortality in herring
larvae during rearing experiments, the firut after yolk HUC ahwrption
and the second at 18-20 mm. Both phases occurred denpitr! an ehundant,
though not necessarily suitable, food upp ply. Many fttiluyw f ~ , rwr
clupeid larvae after absorption of the yolk munt haw: hx:n dnr: t r ,
unsatisfactory food, but from cams where 8omc larvw: havc: AIJrviv(!d,
i t would appear that the ability to Burvivo varicH widely from larva to
larva, even from the samc parente. The second phaso of mortality
mentioned above might have bcen due to the imperfect development of
a particular organ system.
At present, proof of the existence of critical periodn for Burviva1 of
larvae in the sea must await the development of a sufficiently continuous and comprehensive sampling programme on a larval population.
Clearly, however, the survival of a brood must depend on a number of
factors, two of which are feeding, which has already been discussed, and
predation.