32
J. E. SHELBOURNE
production substantially during 1960, they were replaced by nine
162 cm x 61 cm x 61 cm black polythene tanks disposed in three rows
of three on steel supports. Each tank held 460 1. sea water, boosting
the circuit capacity from 11 000 to 16 760 1. The inverted filter funnel,
for screening the outlet, was replaced by a new system with an increased
surface area to prevent blockage. The vertical limb of the submerged
outlet pipe was perforated along part of its length, the lower end corked,
and the perforations screened with a 61 meshes/cm nylon bag held at
a distance from the pipe with polythene discs. Tanks received dim
illumination through two slits in a plastic-faced hardboard cover.
One of the main shortcomings of the 1969 set-up had been the
lack of control over sudden increases in water temperature during
sunny weather. Two home-made air coolers were constructed from
domestic refrigerator units, and installed in the hatchery for the 1960
season. They improved temperature control, but were not completely
adequate for the task.
The greenhousc over the reservoir was treated externally with white
water paint to reflect sunlight, and summer water temperatures
decreased accordingly, A further four glass-wool filters were installed
to give a total of eight; and a filtration rate of 1800 l./h. Apart from
these modifications, the reservoir arrangements were essentially the
same in 1960 as in 1969. Perhaps the greatest fault in the 1969-60
circulation was the use of a greenhouse to cover the reservoir. It was
cheap, easily erected, and admitted daylight for algal photosynthesis,
but the practical difficulties of temperature control outweighed these
considerations. Reservoirs and hatcheries should be insulated against
seasonal and diurnal air temperature changes.
An effort was made during the 1961 seaaon to improve water
temperature control in the main reservoir, and also to suppress bacterial growth, with the system illustrated in Fig. 7. A stainless steel
pump re-circulated reservoir sea water at a rate of 2260 l./h, about
half of which ran directly back into the far end of the reservoir, creating
a slow rotatory current. The remaining flow wm by-passed through
a circuit consisting of three ultra-violet sterilizing units, each emptying
into two glass-wool filters. Pairs of filters disoharged into one of three
asbestos-cement tanks (460 1. capacity), each containing two eteel
cooling coils coated with anti-corrosive epoxy resin.
The six cooling coils were linked in series to a compressor driven
by a 3 h.p. eleotric motor, controlled by a floating thermostat. Sea
water overflowed from the cooling tanks back into the reservoir. Thie
system was capable of lowering the reservoir water temperature 0.1"C
in 90 min, against a tendency to rise the same amount in 3 h, at
J. E. SHELBOURNE
production substantially during 1960, they were replaced by nine
162 cm x 61 cm x 61 cm black polythene tanks disposed in three rows
of three on steel supports. Each tank held 460 1. sea water, boosting
the circuit capacity from 11 000 to 16 760 1. The inverted filter funnel,
for screening the outlet, was replaced by a new system with an increased
surface area to prevent blockage. The vertical limb of the submerged
outlet pipe was perforated along part of its length, the lower end corked,
and the perforations screened with a 61 meshes/cm nylon bag held at
a distance from the pipe with polythene discs. Tanks received dim
illumination through two slits in a plastic-faced hardboard cover.
One of the main shortcomings of the 1969 set-up had been the
lack of control over sudden increases in water temperature during
sunny weather. Two home-made air coolers were constructed from
domestic refrigerator units, and installed in the hatchery for the 1960
season. They improved temperature control, but were not completely
adequate for the task.
The greenhousc over the reservoir was treated externally with white
water paint to reflect sunlight, and summer water temperatures
decreased accordingly, A further four glass-wool filters were installed
to give a total of eight; and a filtration rate of 1800 l./h. Apart from
these modifications, the reservoir arrangements were essentially the
same in 1960 as in 1969. Perhaps the greatest fault in the 1969-60
circulation was the use of a greenhouse to cover the reservoir. It was
cheap, easily erected, and admitted daylight for algal photosynthesis,
but the practical difficulties of temperature control outweighed these
considerations. Reservoirs and hatcheries should be insulated against
seasonal and diurnal air temperature changes.
An effort was made during the 1961 seaaon to improve water
temperature control in the main reservoir, and also to suppress bacterial growth, with the system illustrated in Fig. 7. A stainless steel
pump re-circulated reservoir sea water at a rate of 2260 l./h, about
half of which ran directly back into the far end of the reservoir, creating
a slow rotatory current. The remaining flow wm by-passed through
a circuit consisting of three ultra-violet sterilizing units, each emptying
into two glass-wool filters. Pairs of filters disoharged into one of three
asbestos-cement tanks (460 1. capacity), each containing two eteel
cooling coils coated with anti-corrosive epoxy resin.
The six cooling coils were linked in series to a compressor driven
by a 3 h.p. eleotric motor, controlled by a floating thermostat. Sea
water overflowed from the cooling tanks back into the reservoir. Thie
system was capable of lowering the reservoir water temperature 0.1"C
in 90 min, against a tendency to rise the same amount in 3 h, at