THE ARTIFIOIAL PROPAGATION OF MAEWXE FISH
31
of polythene film on a wooden frame with no metal fastenings.
The trays were held in position by nylon cords attached to strong
points outside the reservoir ; their position below the surface could be
adjusted. Sixteen 80-W fluorescent tubes, arranged in four banks
of four above the trays, provided strong illumination for E n t e r m h a
at night. Each bank of lights was supported from a stout timber
gallows spanning the tank, by a nylon rope and pulley system permitting vertical adjustment. The reservoir was aovered by a cheap and
lightly built greenhouse equipped with a controlled heating system
for use in frosty weather. Low wattage immersion heating panels,
completely embedded in epoxy resin and operated by floating thermostats, were used to offset excessive cooling of reservoir water during
the winter months. There were no safeguards against rapidly rising
temperatures during the spring and early summer. Shortly after the
start of the 1959 season, a filtration system was installed. Reservoir
water was pumped at a rate of 900 l./h through glass wool pads in
four polythene containers. Undesirable phytoplankton blooms were
checked in this manner and a low degree of turbidity maintained
for long periods, Replacement increments of offshore se& water were
added to the reservoir from time to time, and also distilled water, in
a vain attempt to offset evaporation and increasing mlinity during
hot weather.
A smell electric pump, under the control of a mercury float switch,
transferred sea water from the main reservoir to a header tank in the
hatchery, from where it was distributed by gravity feed to sixteen
glass incubators arranged in two rows of eight on metal stands. These
incubators were identical with those shown in Fig. 6 for 1957-68.
Water ran back into the reservoir along a common drain tube. The
inside walls of the hatchery were painted white ; overhead illumination
was provided by three glass " blisters " in the roof, augmented by
four 80-W fluorescent tubes. Water baths were not used in the
1959 experiment. Side lighting was cut out by erecting an opaque
cloth screen around the cluster of incubators. Thermostat heaters
Prevented excessive air cooling in cold weather ; rising temperatures
in warm weather could not easily be counteracted.
As far as possible, metal surfaces in contact with sea water were
kept to a minimum ; only stainless steel (pump impeller) or chromium
Plate (reservoir thermostats) was used. Copper, brass and aluminium
were strictly avoided. All sea-water conduits were constructed from
Polythene, with glass and rubber inserts.
Although small glass incubators are useful for experimental studies,
they are fragile and difficult to work. In an effort to increase larval
B
'
31
of polythene film on a wooden frame with no metal fastenings.
The trays were held in position by nylon cords attached to strong
points outside the reservoir ; their position below the surface could be
adjusted. Sixteen 80-W fluorescent tubes, arranged in four banks
of four above the trays, provided strong illumination for E n t e r m h a
at night. Each bank of lights was supported from a stout timber
gallows spanning the tank, by a nylon rope and pulley system permitting vertical adjustment. The reservoir was aovered by a cheap and
lightly built greenhouse equipped with a controlled heating system
for use in frosty weather. Low wattage immersion heating panels,
completely embedded in epoxy resin and operated by floating thermostats, were used to offset excessive cooling of reservoir water during
the winter months. There were no safeguards against rapidly rising
temperatures during the spring and early summer. Shortly after the
start of the 1959 season, a filtration system was installed. Reservoir
water was pumped at a rate of 900 l./h through glass wool pads in
four polythene containers. Undesirable phytoplankton blooms were
checked in this manner and a low degree of turbidity maintained
for long periods, Replacement increments of offshore se& water were
added to the reservoir from time to time, and also distilled water, in
a vain attempt to offset evaporation and increasing mlinity during
hot weather.
A smell electric pump, under the control of a mercury float switch,
transferred sea water from the main reservoir to a header tank in the
hatchery, from where it was distributed by gravity feed to sixteen
glass incubators arranged in two rows of eight on metal stands. These
incubators were identical with those shown in Fig. 6 for 1957-68.
Water ran back into the reservoir along a common drain tube. The
inside walls of the hatchery were painted white ; overhead illumination
was provided by three glass " blisters " in the roof, augmented by
four 80-W fluorescent tubes. Water baths were not used in the
1959 experiment. Side lighting was cut out by erecting an opaque
cloth screen around the cluster of incubators. Thermostat heaters
Prevented excessive air cooling in cold weather ; rising temperatures
in warm weather could not easily be counteracted.
As far as possible, metal surfaces in contact with sea water were
kept to a minimum ; only stainless steel (pump impeller) or chromium
Plate (reservoir thermostats) was used. Copper, brass and aluminium
were strictly avoided. All sea-water conduits were constructed from
Polythene, with glass and rubber inserts.
Although small glass incubators are useful for experimental studies,
they are fragile and difficult to work. In an effort to increase larval
B
'