70
J. E. SHELROURNE
VIII. THE MASS-PRODUCTION OF METAMORPHOSED FLATFISH
There are several different ways in which the output of a marine
hatchery could be ntilized to augment natural fish resources. These
will be discussed in the next section. All require a consistent technology
for the annual production of young flatfish on a very large scale indeed.
During the course of the 1962 rearing experiments at Port Erin, a total
of about 26 000 metamorphosed plaice was produced ; plans are now
being laid to push this figure up to 1 million within the next 5 years.
Most of the basic design information for a pilot-plant scheme is
now available. We know, for instance, that 7000+ plaice can metamorphose on l m9 of tank bottom (Table VII). Admittedly, a large
proportion of this stock was imperfectly pigmented in 1962, but I am
optimistic about increasing the degree of normality with proper
environmental control. If a figure of 6000 young plaice/m2 is taken
as a standard, then 200 ma of tank bottom would be required to house
1 million metamorphosed stock. Tanks need only be 30 cm deep.
Say 200 shallow black fibre-glass or polythene tanks of the right
dimensions, each containing 300 1. of sea water, arranged in rows and
layers with adequate lighting, in a simple but well-insulated prefabricated building 16 m x 10 m x 4 m to the eaves. A 3-5 h.p. air cooling
system would be necessary to maintain air temperature at an optimum
within this space during late spring and early summer.
With a practical rate of inflow equal to 10% of the tank volume
per hour, a total delivery of 6000 l,/h sea water would meet hatchery
requirements. In early summer this flow may have to be cooled to a
level 5-7°C below intake temperature before distribution to hatchery
tanks ; a 20 h.p. stainless steel chiller would accomplish this task. A
high-capacity pressure filtration plant would also be desirable, and
possibly a U.V. water sterilizing unit, though the benefits of bacterial
control of incoming sea water have not yet been conclusively demonstrated.
Just before metamorphosis, a fast-growing plaice larva can consume
an average of 200 Artemia nauplii per day. Present indications are
that 200 million ArtemM nauplii can be produced in 36 h by incubating
their eggs in about not more than fifty shallow incubator-separators,
each 1-6 m x 1 m x 0.15 m deep, at a temperature of 23°C. For daily
feeding, twice this number of tanks would be required, and they could be
racked in an insulated space 10 m x 6 m x 4 m to the eaves, maintained at the correct temperature by thermostatically controlled heaters.
The fecundity of the plaice is more closely related to its weight
and the cube of its length, than to its age (Simpson, 1961). A mediumsized female plaice (35 cm) from the Irish Sea may liberate 100 000 eggs
J. E. SHELROURNE
VIII. THE MASS-PRODUCTION OF METAMORPHOSED FLATFISH
There are several different ways in which the output of a marine
hatchery could be ntilized to augment natural fish resources. These
will be discussed in the next section. All require a consistent technology
for the annual production of young flatfish on a very large scale indeed.
During the course of the 1962 rearing experiments at Port Erin, a total
of about 26 000 metamorphosed plaice was produced ; plans are now
being laid to push this figure up to 1 million within the next 5 years.
Most of the basic design information for a pilot-plant scheme is
now available. We know, for instance, that 7000+ plaice can metamorphose on l m9 of tank bottom (Table VII). Admittedly, a large
proportion of this stock was imperfectly pigmented in 1962, but I am
optimistic about increasing the degree of normality with proper
environmental control. If a figure of 6000 young plaice/m2 is taken
as a standard, then 200 ma of tank bottom would be required to house
1 million metamorphosed stock. Tanks need only be 30 cm deep.
Say 200 shallow black fibre-glass or polythene tanks of the right
dimensions, each containing 300 1. of sea water, arranged in rows and
layers with adequate lighting, in a simple but well-insulated prefabricated building 16 m x 10 m x 4 m to the eaves. A 3-5 h.p. air cooling
system would be necessary to maintain air temperature at an optimum
within this space during late spring and early summer.
With a practical rate of inflow equal to 10% of the tank volume
per hour, a total delivery of 6000 l,/h sea water would meet hatchery
requirements. In early summer this flow may have to be cooled to a
level 5-7°C below intake temperature before distribution to hatchery
tanks ; a 20 h.p. stainless steel chiller would accomplish this task. A
high-capacity pressure filtration plant would also be desirable, and
possibly a U.V. water sterilizing unit, though the benefits of bacterial
control of incoming sea water have not yet been conclusively demonstrated.
Just before metamorphosis, a fast-growing plaice larva can consume
an average of 200 Artemia nauplii per day. Present indications are
that 200 million ArtemM nauplii can be produced in 36 h by incubating
their eggs in about not more than fifty shallow incubator-separators,
each 1-6 m x 1 m x 0.15 m deep, at a temperature of 23°C. For daily
feeding, twice this number of tanks would be required, and they could be
racked in an insulated space 10 m x 6 m x 4 m to the eaves, maintained at the correct temperature by thermostatically controlled heaters.
The fecundity of the plaice is more closely related to its weight
and the cube of its length, than to its age (Simpson, 1961). A mediumsized female plaice (35 cm) from the Irish Sea may liberate 100 000 eggs