66
J. E. SHELBOURNE
bacterial growth with the same anti-biotics. Oppenheimer's experiments covered survival to hatching only. The new plaice-rearing
technique made it possible to assess the effects of anti-biotic treatment
on survival to metamorphosis.
Apparatus and methods. On 23 March, three experimental fibreglass units similar to that illustrated in Figs. 12 and 13, each containing three glass incubators, were stocked with pond-spawned
plaice eggs less than 24 h old, at a rate of 1000 blastulae per incubator.
The incubators in units 1 and 2 were treated immediately with sodium
penicillin G and streptomycin sulphate at concentrations of SO international units and 0.06 mg/ml sea water respectively, and left static
for 24 h. Unit 3 was the untreated control. Unit 1 was then irrigated
with hatchery sea water previously sterilized by ultra-violet light,
whilst unit 2 was irrigated with normal hatchery water. Eight days
after the start, unit 1 received a second dose of anti-biotics. The
treatment during egg incubation can be summarized as follows :
Unit 1. 2 doses of anti-biotic mixture; irrigated with U.V.-treated
Unit 2. 1 dose of 'anti-biotic mixture; irrigated with normal
Unit 3. No anti-biotics ; irrigated with normal hatchery sea water.
Incubation temperatures were not strictly controlled, but buffered
by a slow circulation of hatchery sea water around the incubators
contained in the fibre-glass units. Despite this precaution, temperatures
were above optimum, lying within the range 8.6-9.0"C at hatching,
ll-12°C at first-feeding and 14-15"C at metamorphosis. Light conditions during larval feeding were roughly the same for each unit,
approaching 600 lux a t the water surface. Artemia nauplii were fed
daily to all tanks, in quantities sufficient to provide a small residual
food population the following morning.
Results. Figure 15 gives the survival curves for each unit of three
experimental tanks. Treated units 1 and 2 held the advantage at
hatching-97% hatched as against 93% in the untreated controls.
Some unexpected early larval mortalities occurred in unit 1, probably
&B a result of air bubbles baing carried into incubators with inflowing
~ e &
water. By the time non-feeding mortalities had c e d , survivds
in the treated tanks were considerably higher than in the controls, and
this lead was maintained to the end of the experiment. The advantage
held by unit 1 (2 doses anti-biotics + U.V.) over unit 2 (1 dose antibiotics) wm lost during the later larval stages.
Plate cultures of l-ml water samples taken during the course of the
sea water.
hatchery sea water.
J. E. SHELBOURNE
bacterial growth with the same anti-biotics. Oppenheimer's experiments covered survival to hatching only. The new plaice-rearing
technique made it possible to assess the effects of anti-biotic treatment
on survival to metamorphosis.
Apparatus and methods. On 23 March, three experimental fibreglass units similar to that illustrated in Figs. 12 and 13, each containing three glass incubators, were stocked with pond-spawned
plaice eggs less than 24 h old, at a rate of 1000 blastulae per incubator.
The incubators in units 1 and 2 were treated immediately with sodium
penicillin G and streptomycin sulphate at concentrations of SO international units and 0.06 mg/ml sea water respectively, and left static
for 24 h. Unit 3 was the untreated control. Unit 1 was then irrigated
with hatchery sea water previously sterilized by ultra-violet light,
whilst unit 2 was irrigated with normal hatchery water. Eight days
after the start, unit 1 received a second dose of anti-biotics. The
treatment during egg incubation can be summarized as follows :
Unit 1. 2 doses of anti-biotic mixture; irrigated with U.V.-treated
Unit 2. 1 dose of 'anti-biotic mixture; irrigated with normal
Unit 3. No anti-biotics ; irrigated with normal hatchery sea water.
Incubation temperatures were not strictly controlled, but buffered
by a slow circulation of hatchery sea water around the incubators
contained in the fibre-glass units. Despite this precaution, temperatures
were above optimum, lying within the range 8.6-9.0"C at hatching,
ll-12°C at first-feeding and 14-15"C at metamorphosis. Light conditions during larval feeding were roughly the same for each unit,
approaching 600 lux a t the water surface. Artemia nauplii were fed
daily to all tanks, in quantities sufficient to provide a small residual
food population the following morning.
Results. Figure 15 gives the survival curves for each unit of three
experimental tanks. Treated units 1 and 2 held the advantage at
hatching-97% hatched as against 93% in the untreated controls.
Some unexpected early larval mortalities occurred in unit 1, probably
&B a result of air bubbles baing carried into incubators with inflowing
~ e &
water. By the time non-feeding mortalities had c e d , survivds
in the treated tanks were considerably higher than in the controls, and
this lead was maintained to the end of the experiment. The advantage
held by unit 1 (2 doses anti-biotics + U.V.) over unit 2 (1 dose antibiotics) wm lost during the later larval stages.
Plate cultures of l-ml water samples taken during the course of the
sea water.
hatchery sea water.