Aquaculture

Aquaculture

1. Principles

   • Selection of desirable species
   • Control of undesirable species - competitors and predators
   • Provision or encouragement of food
   • Control of abiotic conditions to increase productivity

2. Major Species Examples

   • Carp
   • Salmon
   • Tilapia
   • Trout
   • Shrimp
   • Oysters
   • Mussels

3. Methods

   • Extensive
     • Food production with relatively low inputs
     • Predatory fish/birds may be controlled to an extent and nutrients could be added to water to stimulate growth if the fish's food (plant species)
     • Shellfish could be grown in a captivity before being released into the wild for capture at a later date
   • Intensive
     • A high yield is achieved by controlling all possible limiting factors
     • Fish selectively bred to increase growth rate and enhance desirable characteristics
     • Artificial conditions mean there are no competitors or predators, and pests are controlled
     • Environmental factors that could be limiting factors to productivity are controlled

4. Control of Limiting Factors

   • Temperature - must not get too high, so farms are usually located in areas with cooler climates (e.g. Scotland)
   • Dissolved oxygen - Levels are kept high with water sprays or weirs that agitate the water
   • Water Flow - Farms are usually in areas with strong currents. Helps fish muscle mass by swimming against the current and allows for higher stocking densities
   • Light Levels - Artificial light can be used if the natural supply is not enough to induce smoltification in young fish

5. Environmental Impacts

   • Habitat Impacts
     • Over-fishing of food species causes problems for the food web involved, but also causes damage when taking place - seabed damage from trawling for example
     • Natural predators may be culled if they are seen as pests
     • Parasites from the farm stock could transfer on to wild species which have no antibiotics as protection
     • The construction of the farm itself could destroy existing habitats
     • Introduced species from the farm may compete/predate on organisms in the local environment
     • Fish that escape from the farm may breed with wild fish and alter the gene pool, bringing characteristics that might not be suitable for survival in the wild
   • Pollution
     • Pesticides used can be poisonous to wildlife
     • Overuse of antibiotics could encourage development of resistant pathogens which could transfer on to local fish
     • Organic waste may cause deoxygenation of the water
     • Inorganic waste released in excretion can cause eutrophication