ESTUARINE FISH FARMING
139
portion become mature. As they are unable to shed their eggs in sea
water, most become egg-bound and die, or have to be marketed at
once without regard to the state of the market. As the fish are raised
in cement ponds built at the water’s edge, sea water is easily available
but has to be pumped. Surprisingly, the cost of pumping is given as
6-10% of production costs. On the other hand, the sea water remains
warm in winter, so allowing growth to continue, whereas, in Norway,
the fresh waters become very cold. Though this kind of trout farming is
attractive to Norwegian operators because level ground for fishponds is
so scarce, and though there has been some success, it seems that, at least
as late as 1964, the industry had not got off the ground (Sedgwick, 1964).
Now some Norwegian operators are rearing trout in small floating
enclosures resembling, and probably inspired by, the cages in which
yellowtail are raised in Japan. Control of the fish has proved difficult,
and final success has been wanting. But their example has stimulated
the international edible oil and animal food combine of Unilever to do
some serious trials. They have established a base at Loch Ailort in the
west of Scotland, and a popular account of this venture has been published by Frost (1968).
Rainbow trout eggs from hatcheries in America and elsewhere were
hatched out in conventional fresh-water hatcheries. The alevins were
raised in the usual way in a series of concrete ponds fed by pure fresh
water from the River Ailort, and given finely-minced liver as fodder.
Pumped sea water was gradually admixed with the fresh water as the
young trout grew, until they were fully acclimatized to life in sea water.
Then they were transferred to cages floating in Loch Ailort, and
intensively fed on chopped and minced white fish. The article claims
growth of individual fish t o a weight of 54 Ib in slightly more than two
years. The article also claims that the rate of production of fish p u l d
be as high as 500 tons annually by the autumn of 1970 if the firm took
the decision to go ahead.
Unilever is in a stronger position than most firms to supply
pelleted foods, and it seems that the success of this and other ventures,
possibly such as the raising of sole (Cole, 1968), will depend on the production of a mass-produced and cheap high-protein fodder with high
acceptance and digestibility. The present pelleted trout foods seem
dear for the raising of table fish, and this country seems less fortunate
than Japan in available supplies of abundant cheap trash fish. I n
Sweden, pellets made with a protein basis of purified fish meal and
casein, with kelp meal, fat, yeast and: vitamins, gave the very high rate
of conversion of 1.5 :1, or even better (Carlin, 1966) when fed to young
salmon, but they were expensive.
139
portion become mature. As they are unable to shed their eggs in sea
water, most become egg-bound and die, or have to be marketed at
once without regard to the state of the market. As the fish are raised
in cement ponds built at the water’s edge, sea water is easily available
but has to be pumped. Surprisingly, the cost of pumping is given as
6-10% of production costs. On the other hand, the sea water remains
warm in winter, so allowing growth to continue, whereas, in Norway,
the fresh waters become very cold. Though this kind of trout farming is
attractive to Norwegian operators because level ground for fishponds is
so scarce, and though there has been some success, it seems that, at least
as late as 1964, the industry had not got off the ground (Sedgwick, 1964).
Now some Norwegian operators are rearing trout in small floating
enclosures resembling, and probably inspired by, the cages in which
yellowtail are raised in Japan. Control of the fish has proved difficult,
and final success has been wanting. But their example has stimulated
the international edible oil and animal food combine of Unilever to do
some serious trials. They have established a base at Loch Ailort in the
west of Scotland, and a popular account of this venture has been published by Frost (1968).
Rainbow trout eggs from hatcheries in America and elsewhere were
hatched out in conventional fresh-water hatcheries. The alevins were
raised in the usual way in a series of concrete ponds fed by pure fresh
water from the River Ailort, and given finely-minced liver as fodder.
Pumped sea water was gradually admixed with the fresh water as the
young trout grew, until they were fully acclimatized to life in sea water.
Then they were transferred to cages floating in Loch Ailort, and
intensively fed on chopped and minced white fish. The article claims
growth of individual fish t o a weight of 54 Ib in slightly more than two
years. The article also claims that the rate of production of fish p u l d
be as high as 500 tons annually by the autumn of 1970 if the firm took
the decision to go ahead.
Unilever is in a stronger position than most firms to supply
pelleted foods, and it seems that the success of this and other ventures,
possibly such as the raising of sole (Cole, 1968), will depend on the production of a mass-produced and cheap high-protein fodder with high
acceptance and digestibility. The present pelleted trout foods seem
dear for the raising of table fish, and this country seems less fortunate
than Japan in available supplies of abundant cheap trash fish. I n
Sweden, pellets made with a protein basis of purified fish meal and
casein, with kelp meal, fat, yeast and: vitamins, gave the very high rate
of conversion of 1.5 :1, or even better (Carlin, 1966) when fed to young
salmon, but they were expensive.