20
J . E. SHELBOURNE
year since 1960. His preliminary findings auggeart a positive correlation
between the abundance of O-group cod in the littoral region and hatchery
liberations. None of the years in which larvae were released has yielded
substantially smaller catches than the best of the intervening years.
Dannevig intends to continue this type of experimental approach in
Oalofjord, and to extend it to other coastal arem.
V. THE REARING OF MARINE FISH LARVAE
Hjort and Dahl(1900), in their detailed criticism of sea-fish hatchery
methods as then practised, stressed the fact that despite 20 years
effort, no techniques had been developed for rearing marine fish larvae,
in large numbers, to a tough stage of development suitable for release
into the sea. They went on to say “. . . that if the work of hatching
could be perfected, so that, by its aid, the larvae of the plaice could be
kept alive beyond the pelagic stage, and reared until it settled on the
bottom, a way might thus be found of increasing the stock of this
species on our shores.”
Petersen (1894) had early realized the desirability of improving
hatchery techniques, but after several unsuccessful attempts to rear
plaice, he became convinced that “. . . At the pelagic stage, after the
yolk has been absorbed, it cannot be kept alive in aquaria.” But
already, small numbers of Baltic winter herring had been reared
through metamorphosis from artificially fertilized eggs by Meyer
(1878), in a large tub of sea water, partly refreshed each day. Although
heavy mortalities occurred among the larvae 10 days after hatching,
E few were able to develop on the natural plankton introduced into
the tub with water renewals. After 6 months, survivors had attained
a length of 72 mm ; no mention is m d e of final numbers or survival
rates.
Rognerud (1887) described an experiment by Capt. Dannevig at
Flsdevigen hatchery in which 500000 newly-hatched cod fry were
liberated into a large marine pond. Survivors lived for the first month
on the natural productivity of the pond, but were subsequently fed
on triturated mackerel flesh. After 6 months the mean length w w
116 mm, and several thousands survived 8 months to the end of the
experiment. Garstang (1900) estimated the survival rate to be not
more than 1 or 2%, but pointed out that the experiment served
Dannevig’s purpose, which was to demonstrate that artificially-hatched
ood fry had the power to live, grow and develop when set at liberty.
The same sort of experiment was repeated, with similar results, at
Port Erin hatchery in 1946 (Burd and Jones, 1948).
Hmdd Dannevig (1897) successfully reared a few plaice larvae
J . E. SHELBOURNE
year since 1960. His preliminary findings auggeart a positive correlation
between the abundance of O-group cod in the littoral region and hatchery
liberations. None of the years in which larvae were released has yielded
substantially smaller catches than the best of the intervening years.
Dannevig intends to continue this type of experimental approach in
Oalofjord, and to extend it to other coastal arem.
V. THE REARING OF MARINE FISH LARVAE
Hjort and Dahl(1900), in their detailed criticism of sea-fish hatchery
methods as then practised, stressed the fact that despite 20 years
effort, no techniques had been developed for rearing marine fish larvae,
in large numbers, to a tough stage of development suitable for release
into the sea. They went on to say “. . . that if the work of hatching
could be perfected, so that, by its aid, the larvae of the plaice could be
kept alive beyond the pelagic stage, and reared until it settled on the
bottom, a way might thus be found of increasing the stock of this
species on our shores.”
Petersen (1894) had early realized the desirability of improving
hatchery techniques, but after several unsuccessful attempts to rear
plaice, he became convinced that “. . . At the pelagic stage, after the
yolk has been absorbed, it cannot be kept alive in aquaria.” But
already, small numbers of Baltic winter herring had been reared
through metamorphosis from artificially fertilized eggs by Meyer
(1878), in a large tub of sea water, partly refreshed each day. Although
heavy mortalities occurred among the larvae 10 days after hatching,
E few were able to develop on the natural plankton introduced into
the tub with water renewals. After 6 months, survivors had attained
a length of 72 mm ; no mention is m d e of final numbers or survival
rates.
Rognerud (1887) described an experiment by Capt. Dannevig at
Flsdevigen hatchery in which 500000 newly-hatched cod fry were
liberated into a large marine pond. Survivors lived for the first month
on the natural productivity of the pond, but were subsequently fed
on triturated mackerel flesh. After 6 months the mean length w w
116 mm, and several thousands survived 8 months to the end of the
experiment. Garstang (1900) estimated the survival rate to be not
more than 1 or 2%, but pointed out that the experiment served
Dannevig’s purpose, which was to demonstrate that artificially-hatched
ood fry had the power to live, grow and develop when set at liberty.
The same sort of experiment was repeated, with similar results, at
Port Erin hatchery in 1946 (Burd and Jones, 1948).
Hmdd Dannevig (1897) successfully reared a few plaice larvae