Control of undesirable species - competitors and predators
Provision or encouragement of food
Control of abiotic conditions to increase productivity
Major Species Examples
Carp
Salmon
Tilapia
Trout
Shrimp
Oysters
Mussels
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
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
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