THE BEHAVIOUR AND FHYSIOLOQY OF IIERRMQ AND OTHER CLUPEIDS 273
E. Egg mortality
1. Egg density
Lea (1030) and Runnstr~m (1941b) showed that overcrowding of
herring eggs on the sea bed off Norway resulted in a high mortality.
Eggs in layers 0.6-2.5 cm thick showed mortalities of 4340%. Cleaver
and Franett (no date) found a similar occurrence in eggs of Clupea
p a h i deposited in large clumps inshore. However, Parrish et al.
(1959), who succeeded in taking egg samples by grab on the Scottish
west coast, found no evidence of a differential mortality in eggs four to
eight layers thick (i.e. 0-5-1.0 cm). McMynn and Hoar (1053) and
Blaxter (1950, 1962) showed that tho succcssful hatching of eggs of
Clupca pallasii and Scottish herring respectively in aquaria depended to
some extent on the density, crowding resulting in a low percentage
hatch. In particular, the former authors found what appeared to be an
intermediate optimum density for the best hatching ; above and below
this percentage hatch was reduced.
2. Fungal and bacterial attack
Toom (1958) found that eggs of Baltic herring were liable to attack
by fungi when kept in the sea away from the spawning ground, although
on the spawning ground they were not affected. In rearing experiments
on herring fungal attack may reduce percentage hatching considerably,
especially when the incubation period is long. Anon. (1952) reported on
the high rate of infection by bacteria of some Sardinope caerulea eggs,
and showed that this could be checked in aquaria by antibioticn.
3. Predation
Reports of fish with their &omactis gorgc:d with twriiig 1:gp arc
to be foirntl iri tho litcrtitiiro ; iridecd concc:ritriitiotiH of hetlilook anti
coal fish were one of thc fir& means of locnting hcrrirlg np~wnirrg
grounds (e.g. Bowman, 1923). Even the stomach8 of qmwriing hcrririg
sometimes contain eggs. Parrish et al. (1959) found on a herring
spawning ground with a heavy population of ophiuroids that the ophiuroids were inversely distributed in relation to the eggs. The eggs of
Clupeu pullasii are deposited inshore (e.g. Rounsefell, 1930) and are
liable to be eaten by birds at lo& tide (Cleaver and Franett, no date).
Presumably the hazards facing demersal and pelagic eggs are somewhat different, the former being concentrated and available in large
quantities, the latter being dispersed, at least some time after spawning,
and yet liable to stranding.
E. Egg mortality
1. Egg density
Lea (1030) and Runnstr~m (1941b) showed that overcrowding of
herring eggs on the sea bed off Norway resulted in a high mortality.
Eggs in layers 0.6-2.5 cm thick showed mortalities of 4340%. Cleaver
and Franett (no date) found a similar occurrence in eggs of Clupea
p a h i deposited in large clumps inshore. However, Parrish et al.
(1959), who succeeded in taking egg samples by grab on the Scottish
west coast, found no evidence of a differential mortality in eggs four to
eight layers thick (i.e. 0-5-1.0 cm). McMynn and Hoar (1053) and
Blaxter (1950, 1962) showed that tho succcssful hatching of eggs of
Clupca pallasii and Scottish herring respectively in aquaria depended to
some extent on the density, crowding resulting in a low percentage
hatch. In particular, the former authors found what appeared to be an
intermediate optimum density for the best hatching ; above and below
this percentage hatch was reduced.
2. Fungal and bacterial attack
Toom (1958) found that eggs of Baltic herring were liable to attack
by fungi when kept in the sea away from the spawning ground, although
on the spawning ground they were not affected. In rearing experiments
on herring fungal attack may reduce percentage hatching considerably,
especially when the incubation period is long. Anon. (1952) reported on
the high rate of infection by bacteria of some Sardinope caerulea eggs,
and showed that this could be checked in aquaria by antibioticn.
3. Predation
Reports of fish with their &omactis gorgc:d with twriiig 1:gp arc
to be foirntl iri tho litcrtitiiro ; iridecd concc:ritriitiotiH of hetlilook anti
coal fish were one of thc fir& means of locnting hcrrirlg np~wnirrg
grounds (e.g. Bowman, 1923). Even the stomach8 of qmwriing hcrririg
sometimes contain eggs. Parrish et al. (1959) found on a herring
spawning ground with a heavy population of ophiuroids that the ophiuroids were inversely distributed in relation to the eggs. The eggs of
Clupeu pullasii are deposited inshore (e.g. Rounsefell, 1930) and are
liable to be eaten by birds at lo& tide (Cleaver and Franett, no date).
Presumably the hazards facing demersal and pelagic eggs are somewhat different, the former being concentrated and available in large
quantities, the latter being dispersed, at least some time after spawning,
and yet liable to stranding.