Transcript All the Fish in the Sea - University of Hong Kong

All the Fish in the Sea
YSTCN0001
Fish
• Fresh water
• Salt water
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Pelagic, upper water layers, 20% fat
Herring, mackeral, tuna, salmon, sardines
Demersal, bottom fish, 5% fat
Cod, haddock, whiting, flat-fish,
• Fish composition varies with season
Declining rate of increase in fishery production
World Fisheries
• Dominated by marine catch
• Decline in rates of production
• Since 1990 no increase in catch
Fresh Fish?
• From oceans
• Fished increasingly by long range trawlers
• Can remain on ice in hold until ship returns
to port
• 1 to 3 weeks
Fish
• Fish flesh readily digested
• deteriorates rapidly
• can be kept on ice for 12 days
Spoilage
• Fish bacteria adapted to living in cold
conditions and can grow under refrigeration
• Fish straight from the water have little odour
• Odour due to develops due to production of
trimethylamine by enzymatic action on fat
phospholipids
• Fish fat polyunsaturated and easily oxidised
Processing
• Preferably gutted and frozen -20°C within 2
hours of catch
• Generally kept in hold on layers of ice
• Sometimes use brine at -12°C
• Often gutted onshore near dockside
Storage
• Low fat fish kept at -20°C for 2 years
• Oily fish best for canning, eg tuna, after
cooking has shelf-life of several years
Preservation
• Salting,~ herrings
• Smoking,~ haddock, salmon
• Drying
Why the Decline?
• Technology
• Overcapitalisation
• Supply & demand
• Poor management
• Wasteful & destructive fishing
= Overfishing
By-catch
• Target catch eg. Shrimps
• Shrimps are small, need to use a fine mesh net
• Any other fish larger than shrimps can also be
caught
• These are the by-catch
F
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d
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s
b
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C
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Solutions
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Management for sustainable fisheries
Reduction of over-fishing
Improvement in fish farming (mariculture)
Reduction of subsidies
More selective fishing methods