THE ARTIFICIAL PROPAGATION OF MARINE FISH
46
progress towards large-scale plaice production. Both these conditions
could be met at the Marine Biological Station, Port Erin, Isle of Man,
which enjoys a hatchery tradition extending back to 1902. The Director,
~. J. S. Colman, was approached ; with his approval a straightforward
experiment was arranged, to test the Loweetoft rearing teohnique in
open circulation, using pond-spawned eggs.
1, Preliminary experiment: 1960
A row of six 60 om x 30 om x 30 om moulded glass tanks, similar
to those used at Lowestoft, was supplied with filtered sea water through
a polythene main trunk at a controlled rate of 4 1.F per tank, from a
constant-level header. Each tank waa fitted with an outer jacket of
black polythene film and with1 a plastic cover, similarly blacked out
except for a central slit 16 cm x 7-6 cm. All tanks rested on a dull
black surface. Light was not strictly controlled. Diffuse daylight
reflected from hatchery walls and ceiling was the main source of tank
illumination, occasionally augmented by overhead tungsten lamps on
dull days.
Water ran into each tank through 3-mm bore tube passing through
a hole in the cover, and delivering below the surface. The outlet
(strictly, overflow) pipe was a similar piece of threaded polythene tube,
secured through a hole in one end of the tank by polythene nuts and
rubber seals, giving a watertight fit. The internal end of the outlet
pipe was inserted in the horizontal limb of a tubular polythene rightangle, the perforated vertical limb of which wu surrounded at a
distance by a 61 mesheslcm nylon screen on a plastic frame. By this
arrangement it was possible to irrigate the tank with a constant flow
of sea water without flushing away eggs, larvae and naupliar food.
The outflow of each tank ran to waste through a T-pieoe lesding to a
common drain tube.
The Port Erin station is equipped with two main spawning ponds.
During the autumn of 1969, part of a captive plaice stook which had
Spawned the previous season was transferred to the east pond to overwinter. These fish were fed with boiled mussel from time to time, md
the pond occasionally topped up. Just before the stmt of the 1960
semon in the Irish Sea, ripening plaice were trawled from
Offahore grounds and used to stock the west pond. Pond spawning
in early March and lasted until mid-April. On 8 April the six
glass incubators were stocked ES follows :
Tank 1. 2000 mid-stage eggs (gastrulae) from pond-wintered stock
2. 1000 mid-stage eggs (gastrulae) from pond-wintered stook
46
progress towards large-scale plaice production. Both these conditions
could be met at the Marine Biological Station, Port Erin, Isle of Man,
which enjoys a hatchery tradition extending back to 1902. The Director,
~. J. S. Colman, was approached ; with his approval a straightforward
experiment was arranged, to test the Loweetoft rearing teohnique in
open circulation, using pond-spawned eggs.
1, Preliminary experiment: 1960
A row of six 60 om x 30 om x 30 om moulded glass tanks, similar
to those used at Lowestoft, was supplied with filtered sea water through
a polythene main trunk at a controlled rate of 4 1.F per tank, from a
constant-level header. Each tank waa fitted with an outer jacket of
black polythene film and with1 a plastic cover, similarly blacked out
except for a central slit 16 cm x 7-6 cm. All tanks rested on a dull
black surface. Light was not strictly controlled. Diffuse daylight
reflected from hatchery walls and ceiling was the main source of tank
illumination, occasionally augmented by overhead tungsten lamps on
dull days.
Water ran into each tank through 3-mm bore tube passing through
a hole in the cover, and delivering below the surface. The outlet
(strictly, overflow) pipe was a similar piece of threaded polythene tube,
secured through a hole in one end of the tank by polythene nuts and
rubber seals, giving a watertight fit. The internal end of the outlet
pipe was inserted in the horizontal limb of a tubular polythene rightangle, the perforated vertical limb of which wu surrounded at a
distance by a 61 mesheslcm nylon screen on a plastic frame. By this
arrangement it was possible to irrigate the tank with a constant flow
of sea water without flushing away eggs, larvae and naupliar food.
The outflow of each tank ran to waste through a T-pieoe lesding to a
common drain tube.
The Port Erin station is equipped with two main spawning ponds.
During the autumn of 1969, part of a captive plaice stook which had
Spawned the previous season was transferred to the east pond to overwinter. These fish were fed with boiled mussel from time to time, md
the pond occasionally topped up. Just before the stmt of the 1960
semon in the Irish Sea, ripening plaice were trawled from
Offahore grounds and used to stock the west pond. Pond spawning
in early March and lasted until mid-April. On 8 April the six
glass incubators were stocked ES follows :
Tank 1. 2000 mid-stage eggs (gastrulae) from pond-wintered stock
2. 1000 mid-stage eggs (gastrulae) from pond-wintered stook