THE ARTIFXOIAL PROPAQATION OF MARINE PISH
11
Surviving larvae were transferred from incubators to transportation
cans and usually liberated in local waters. The US. Fish Commission
reports for 1886 and 1886 contain accounts of a spectaoular but
unsuccessful attempt to establish a cod fishery in the Gulf of Mexioo,
using newly-hatched cod fry from the east-coast hatcheries. !Craneprtation losses were only 10%.
B. European method8
In its day, the Norwegian hatchery at Fledevigen was probably
the best designed institution of its kind in the woxld. Detailed accounts
of layout, apparatus and methods have been given by its founder,
Capt. G. M. Dannevig (1910a) and,his successor, Alf. Dannevig (1928).
1. Egg WPPlY
Each January, ripening cod were purchased from the merchants
of Arendal fish market, and transferred to the hatchery spawning
pond (capacity 350 000 1.). The pond could hold 2000 medium-sized
fish and was usually stocked in the proportion one male to four females.
Chopped herring was offered as food, and the pond irrigated with
fiord sea water at a rate of 30 000 lfhr.
Cod usually spawn at night; after fertilization, eggs were automatically carried into a colbcting device by outflowing surface currents.
Capt. Dannevig freed egg batches from swface scum and floating
detritus by adding fresh water to sea water in the collectors. Eggs
sank under the new conditions of decreased salinity ; the water surface
was then cleaned, sea water added to refloat the eggs, and the stock
distributed among specially designed incubators in the hatchery.
This system was a good deal simpler and less laborious than the
American I ‘ stripping ” technique ; it also guaranteed a high percentage
fertilization of fully-ripe eggs. At the same time, annual production
could still be influenced by uncontrolled variables in the pondsalinity, temperature and turbidity, in particular. The practice of
renewing the spawning stock each year may also have been detrimental; Harald Dannevig (1896) in Scotland, commented on the
superior quality of eggs obtained from captive spawners fully aoclimatized to pond conditions by lengthy reeidenoe.
2. Egg incubation
A basic unit of the Dannevig egg-hatching apparatus is illustrated
in Fig. 2. It consisted of a watertight wooden trough (2.30 m X 70 cm
X 20 cm deep) divided longitudinally, with both halves connected at
the upper (supply) and lower (outflow) ends by common pockets. Both
11
Surviving larvae were transferred from incubators to transportation
cans and usually liberated in local waters. The US. Fish Commission
reports for 1886 and 1886 contain accounts of a spectaoular but
unsuccessful attempt to establish a cod fishery in the Gulf of Mexioo,
using newly-hatched cod fry from the east-coast hatcheries. !Craneprtation losses were only 10%.
B. European method8
In its day, the Norwegian hatchery at Fledevigen was probably
the best designed institution of its kind in the woxld. Detailed accounts
of layout, apparatus and methods have been given by its founder,
Capt. G. M. Dannevig (1910a) and,his successor, Alf. Dannevig (1928).
1. Egg WPPlY
Each January, ripening cod were purchased from the merchants
of Arendal fish market, and transferred to the hatchery spawning
pond (capacity 350 000 1.). The pond could hold 2000 medium-sized
fish and was usually stocked in the proportion one male to four females.
Chopped herring was offered as food, and the pond irrigated with
fiord sea water at a rate of 30 000 lfhr.
Cod usually spawn at night; after fertilization, eggs were automatically carried into a colbcting device by outflowing surface currents.
Capt. Dannevig freed egg batches from swface scum and floating
detritus by adding fresh water to sea water in the collectors. Eggs
sank under the new conditions of decreased salinity ; the water surface
was then cleaned, sea water added to refloat the eggs, and the stock
distributed among specially designed incubators in the hatchery.
This system was a good deal simpler and less laborious than the
American I ‘ stripping ” technique ; it also guaranteed a high percentage
fertilization of fully-ripe eggs. At the same time, annual production
could still be influenced by uncontrolled variables in the pondsalinity, temperature and turbidity, in particular. The practice of
renewing the spawning stock each year may also have been detrimental; Harald Dannevig (1896) in Scotland, commented on the
superior quality of eggs obtained from captive spawners fully aoclimatized to pond conditions by lengthy reeidenoe.
2. Egg incubation
A basic unit of the Dannevig egg-hatching apparatus is illustrated
in Fig. 2. It consisted of a watertight wooden trough (2.30 m X 70 cm
X 20 cm deep) divided longitudinally, with both halves connected at
the upper (supply) and lower (outflow) ends by common pockets. Both