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One of the most rapidly growing industries in the UK today is that of fish farming (also called aquaculture, although this term also includes shellfish and crustacea farming). These fish farms are either raising trout or salmon, although experiments are being carried out into rearing other species such as halibut and turbot. The industry in the UK is dominated by salmon farming, which takes place mostly in Scotland. However, the current UK production of 83,000 tonnes each year is small by comparison with Norway where the annual production is 220,000 tonnes. An indication of the speed of the development of salmon fish farming in the UK is given in Table 13 and Figure 16. World-wide, the production of seafood
Figure 17. Growth of Atlantic salmon farming in Scotland, 1980-94
Crown copyright. Reproduced with the permission of the FRS Marine Laboratory,
Aberdeen, Scotland by aquaculture amounts to 115.9 million tonnes.1 China dominates the market with an output of 27.3 million tonnes and much of the worldwide production is accounted for by shrimp farming (21 million tonnes).
Table 13. Annual UK production of salmon by aquaculture
Salmon produced (tonnes)
1982 1988 1991 1996
2,000 18,000 52,000 83,000 132,000
Fish farming was probably started by the Chinese 4,000 years ago but in Britain there are early records of trout and carp being reared in monastery ponds to provide fish for the monks on meatless days, special feast days and for Lent. The first experiments in raising salmon in tanks started in the 1960s but it took more than ten years before it became a viable commercial venture.
In the UK, fish farming is largely confined to raising salmon and trout, and each fish has different requirements for successful rearing. Trout farming is a much smaller industry than salmon farming: in 1996, just over 4,000 tonnes were produced.
The salmon farm attempts to reproduce the natural life cycle of the salmon which is shown in Figure 18, but accelerates it by the use of artificial feed, heat and lighting. The 'broodstock', i.e. the hen salmon full of eggs and the cock salmon which will be used to fertilize them, are moved from their sea cages to freshwater. The eggs are stripped from the female and subsequently fertilized by the male's milt. The fertilized eggs are kept in trays over which flows high purity water. When hatched, the fry are kept in freshwater tanks and fed an artificial diet.
After about 18 months, the young fish become smolts and are then transferred to cages moored in sea lochs. Again, they are fed with a specialized diet and grow rapidly to marketable size after about two years at sea.
The sea cages are normally circular or rectangular structures from which are suspended strong nets to a depth of 10-15 metres (Cover
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