42
J. E. SHELBOURNE
between flexed strips of 1-mm thick polythene, fixed to opposite walls.
One half-the egg incubator-was fitted with two aerators, a thermostatioally controlled aquarium heater, an outlet pipe and a light-proof
lid ; the other half-the separator-with a large plastic helical wheel
for stirring, and an outlet pipe.
In operation, the box was filled with sea water to a desired depth,
the central partition pushed down tightly on to a fixed rubber strip
athwart tho box floor, and a calculated quantity of Artemia eggs added
to the incubator compartment. A concentration of 0.75 g eggs per litre
of water in the incubator gave high percentage hatchings. The lid
was then fixed in position and the air and heat switched on. After
44 h at 23"C, the air and heat were switched off and the incubator
contents allowed to settle. The separator was then illuminated with
a 60-W tungsten filament lamp, and the plastic partition cautiously
raised, not more than 1 cm-at a time. Artemia nauplii swam under the
partition towards the light ; separation from hatching debris was usually
oomplete within 90 min. The partition was then firmly closed, and
for controlled feeding experiments, the stirrer operated and I-ml
samples withdrawn from the separator for population density counts.
Otherwise, the hatch was run off through 61 mesheslcm nylon fabric
to concentrate the nauplii, washed in clean sea water, re-suspended,
and acclimatized to tank temperatures before being fed to the fish.
Gentle aeration of concentrated Artemia is recommended. Two or
three successive hatches can be obtained from the same sea water, if
in short supply, but best results demand water renewal for each hatch.
When daily feeding is the routine, two hatching boxes are required,
since the production cycle takes two days.
Plaice larvae can be reared beyond metamorphosis on Artemia
nauplii alone. Metanquplii and adults were used for further growth
and fattening. SeveraI 450-1. asbestos-cement tanks filled with sea
water were enriched with 0.5-1-0 kg dead mussels and placed in a
sunny position outside. Temperatures were maintained between 12'
and 16°C with controlled aquarium heaters. A thick flagellate population, mainly Tetraelmis and Dunalielb spp., appeared within
3 weeks, after which Artemia nauplii and unhatched eggs were added,
and the temperature raised to 18OC. Artemia grow rapidly in these
oonditions; metanauplii were ready for cropping after 2 weeks. By
this time the flagellate population had been grazed down, so mixed
oultures of baker's yeast and the alga Pkodactylurn tricorndum were
d d e d whenever the clarity of the water indicated food shortage. Adult
Artemillr may be too large to be swallowed by plaice larvae less than 26
mm long. They are, however, attacked, killed and eaten piecemeal.
J. E. SHELBOURNE
between flexed strips of 1-mm thick polythene, fixed to opposite walls.
One half-the egg incubator-was fitted with two aerators, a thermostatioally controlled aquarium heater, an outlet pipe and a light-proof
lid ; the other half-the separator-with a large plastic helical wheel
for stirring, and an outlet pipe.
In operation, the box was filled with sea water to a desired depth,
the central partition pushed down tightly on to a fixed rubber strip
athwart tho box floor, and a calculated quantity of Artemia eggs added
to the incubator compartment. A concentration of 0.75 g eggs per litre
of water in the incubator gave high percentage hatchings. The lid
was then fixed in position and the air and heat switched on. After
44 h at 23"C, the air and heat were switched off and the incubator
contents allowed to settle. The separator was then illuminated with
a 60-W tungsten filament lamp, and the plastic partition cautiously
raised, not more than 1 cm-at a time. Artemia nauplii swam under the
partition towards the light ; separation from hatching debris was usually
oomplete within 90 min. The partition was then firmly closed, and
for controlled feeding experiments, the stirrer operated and I-ml
samples withdrawn from the separator for population density counts.
Otherwise, the hatch was run off through 61 mesheslcm nylon fabric
to concentrate the nauplii, washed in clean sea water, re-suspended,
and acclimatized to tank temperatures before being fed to the fish.
Gentle aeration of concentrated Artemia is recommended. Two or
three successive hatches can be obtained from the same sea water, if
in short supply, but best results demand water renewal for each hatch.
When daily feeding is the routine, two hatching boxes are required,
since the production cycle takes two days.
Plaice larvae can be reared beyond metamorphosis on Artemia
nauplii alone. Metanquplii and adults were used for further growth
and fattening. SeveraI 450-1. asbestos-cement tanks filled with sea
water were enriched with 0.5-1-0 kg dead mussels and placed in a
sunny position outside. Temperatures were maintained between 12'
and 16°C with controlled aquarium heaters. A thick flagellate population, mainly Tetraelmis and Dunalielb spp., appeared within
3 weeks, after which Artemia nauplii and unhatched eggs were added,
and the temperature raised to 18OC. Artemia grow rapidly in these
oonditions; metanauplii were ready for cropping after 2 weeks. By
this time the flagellate population had been grazed down, so mixed
oultures of baker's yeast and the alga Pkodactylurn tricorndum were
d d e d whenever the clarity of the water indicated food shortage. Adult
Artemillr may be too large to be swallowed by plaice larvae less than 26
mm long. They are, however, attacked, killed and eaten piecemeal.