THE ARTIFICIAL PROPAOATION OF MARINE FISH
71
(Bagenal, 1960) ; taking the Irish Sea stock as an example, then twenty
medium-sized females could thcoretically produce all the eggs needed
to stock a hatchery designed to rear 1 million metamorphosed fish
at a 60% survival rate. In practico, it may be necessary to oull the
developing larvae in some way, to eliminate incompetent forms.
Even if, in the process, final survival drops to 20% of original eggs, a
mere fifty captive females could meet requirements. Dannevig (191Oa)
stocked ripe female and male cod in the ratio 4 : 1. If the same sex
proportions give 100% fertilization in the case of the plaice, then no
more than sixty-five fish need be maintained from year to year.
The optimum environmental conditions for a captive stock, in order
to ensure an annual maximum yield of high quality eggs, are not yet
known ; one of the most urgent tasks in our sea-fish culture programme
is to discover these criteria. The necessary facilities to do this work
will be included in a new hatchery at Port Erin, now under construction.
To cut expensive labour costs and to increase efficiency, the routine
processes of tank cleaning, egg collection, larval food production and
distribution, etc., will be automated as far as possible. It is by development along these lines, using the advantages of modern technology,
that consistent and economic target production is likely to be achieved.
Although the proposed hatchery will be devoted primarily to the production of baby plaice in the spring of each year, we intend to follow
up with rearing programmes on summer spawners, such as the sole and
turbot.
IX. TOWARDS MARINE FISH FARMING
Assuming we succeed in raising our experimental technique for
rearing plaice to the status of a mass-production technology-and no
insuperable difficulties are foreseen-then there are three main ways
in which hatchery output could be utilized :
1. Mass liberations of young into coastal fisheries to augment
natural recruitment.
2. Release into partly-enclosed coastal waters in an attempt to
establish new nursery grounds, preferably coupled with measures
to increase the basic fertility of the area.
3. Providing the stock for fish domestication projects, involving
further fattening in shore ponds under optimum conditions for
growth all the year round.
A. Augmenting natural recruitment
The rapid recuperation of near-water plaice stocks during periods
Of relaxed fishing effort suggests that our coastal waters could support
71
(Bagenal, 1960) ; taking the Irish Sea stock as an example, then twenty
medium-sized females could thcoretically produce all the eggs needed
to stock a hatchery designed to rear 1 million metamorphosed fish
at a 60% survival rate. In practico, it may be necessary to oull the
developing larvae in some way, to eliminate incompetent forms.
Even if, in the process, final survival drops to 20% of original eggs, a
mere fifty captive females could meet requirements. Dannevig (191Oa)
stocked ripe female and male cod in the ratio 4 : 1. If the same sex
proportions give 100% fertilization in the case of the plaice, then no
more than sixty-five fish need be maintained from year to year.
The optimum environmental conditions for a captive stock, in order
to ensure an annual maximum yield of high quality eggs, are not yet
known ; one of the most urgent tasks in our sea-fish culture programme
is to discover these criteria. The necessary facilities to do this work
will be included in a new hatchery at Port Erin, now under construction.
To cut expensive labour costs and to increase efficiency, the routine
processes of tank cleaning, egg collection, larval food production and
distribution, etc., will be automated as far as possible. It is by development along these lines, using the advantages of modern technology,
that consistent and economic target production is likely to be achieved.
Although the proposed hatchery will be devoted primarily to the production of baby plaice in the spring of each year, we intend to follow
up with rearing programmes on summer spawners, such as the sole and
turbot.
IX. TOWARDS MARINE FISH FARMING
Assuming we succeed in raising our experimental technique for
rearing plaice to the status of a mass-production technology-and no
insuperable difficulties are foreseen-then there are three main ways
in which hatchery output could be utilized :
1. Mass liberations of young into coastal fisheries to augment
natural recruitment.
2. Release into partly-enclosed coastal waters in an attempt to
establish new nursery grounds, preferably coupled with measures
to increase the basic fertility of the area.
3. Providing the stock for fish domestication projects, involving
further fattening in shore ponds under optimum conditions for
growth all the year round.
A. Augmenting natural recruitment
The rapid recuperation of near-water plaice stocks during periods
Of relaxed fishing effort suggests that our coastal waters could support