THE ARTIFICIAL PROPAGATION OF MARINE FISH
73
communication). Tetracyclines are broad-spectrum antibiotics, readily taken up and retained in developing bony structures
(Milch et al., 1968 ; Frost and Villaneuva, 1960). Without a practical
tagging technique for very small fish en masse, the difficulties of
distinguishing between natural and hatchery brood, and, in consequence, of determining the degree of post-liberation dispersal, will
y ~ j u d i c e the chances of accurate stock-taking in the field. It might
then be necessary to saturate a small sea area with hatchery young,
end compare the diminution in numbers of brood as time goes on,
with that in an adjacent control area. Assuming, of course, previous
surveys have shown comparable natural recruitment over a period
of years in both localities. Exercises of this sort should provide urgently
needed information about plaice mortalities during the first 8 or
g months after liberation, from which working estimates of the
economic impact of artificial propagation could be made.
B . Developing new nursery grounds
Ptaice migrations before spawning serve to maintain the stock in a
widely-defined geographical locality, against the dispersal effects of
the prevailing currents, acting on the pelagic phase. Thus the areas
in which young fish accumulate after pelagic life-the inshore nursery
grounds-may be largely determined by regional hydrographic conditions. For example, the offspring of spawning plaice in the southern
North Sea usually end up as 0-group fish on the Dutch, German and
Danish coasts, as a result of north-easterly drift in the current issuing
through the Straits of Dover, backed by the prevailing S.W. winds.
Considerable stretches of the East Anglian coast may therefore remain
virtually unexploited by young plaice ; there is no evidence to suggest
that such areas are basically unsuitable for survival and growth.
The abundance of benthic food acceptable to young plaice, will, of
course, set a limit to the productivity of a nursery ground, but we
already know that semi-enclosed bodies of water can be enriched by
the application of agricultural fertilizers. The late Dr. Fabius Gross
(19474 b ; 1950a, b) and his co-workers (Orr, 1947; Marshall, 1947;
Raymont, 1947, 1960; Nutman, 1960; and Gauld, 1950) raised the
basic fertility of two Scottish sea-lochs during and after the 1939-46
War, producing impressive increases in the abundance of plankton and
benthos, followed by an equally remarkable acceleration in growth
rate of transplanted and resident fish stocks. Buljan (1961), wing a
refined fertilizer application technique in Adriatic bays, has recently
%)roved both the survival rate and growth rate of wild shellfish
Populations.
73
communication). Tetracyclines are broad-spectrum antibiotics, readily taken up and retained in developing bony structures
(Milch et al., 1968 ; Frost and Villaneuva, 1960). Without a practical
tagging technique for very small fish en masse, the difficulties of
distinguishing between natural and hatchery brood, and, in consequence, of determining the degree of post-liberation dispersal, will
y ~ j u d i c e the chances of accurate stock-taking in the field. It might
then be necessary to saturate a small sea area with hatchery young,
end compare the diminution in numbers of brood as time goes on,
with that in an adjacent control area. Assuming, of course, previous
surveys have shown comparable natural recruitment over a period
of years in both localities. Exercises of this sort should provide urgently
needed information about plaice mortalities during the first 8 or
g months after liberation, from which working estimates of the
economic impact of artificial propagation could be made.
B . Developing new nursery grounds
Ptaice migrations before spawning serve to maintain the stock in a
widely-defined geographical locality, against the dispersal effects of
the prevailing currents, acting on the pelagic phase. Thus the areas
in which young fish accumulate after pelagic life-the inshore nursery
grounds-may be largely determined by regional hydrographic conditions. For example, the offspring of spawning plaice in the southern
North Sea usually end up as 0-group fish on the Dutch, German and
Danish coasts, as a result of north-easterly drift in the current issuing
through the Straits of Dover, backed by the prevailing S.W. winds.
Considerable stretches of the East Anglian coast may therefore remain
virtually unexploited by young plaice ; there is no evidence to suggest
that such areas are basically unsuitable for survival and growth.
The abundance of benthic food acceptable to young plaice, will, of
course, set a limit to the productivity of a nursery ground, but we
already know that semi-enclosed bodies of water can be enriched by
the application of agricultural fertilizers. The late Dr. Fabius Gross
(19474 b ; 1950a, b) and his co-workers (Orr, 1947; Marshall, 1947;
Raymont, 1947, 1960; Nutman, 1960; and Gauld, 1950) raised the
basic fertility of two Scottish sea-lochs during and after the 1939-46
War, producing impressive increases in the abundance of plankton and
benthos, followed by an equally remarkable acceleration in growth
rate of transplanted and resident fish stocks. Buljan (1961), wing a
refined fertilizer application technique in Adriatic bays, has recently
%)roved both the survival rate and growth rate of wild shellfish
Populations.