Comparison Of Extensive And Intensive Aquaculture Systems Flashcards
What type of aquaculture is typically extensive?
Oyster farms with low inputs
Filter planktonic organisms form seawater
What is done with breeding in some oyster farms?
Young oysters are bred from selected adults
Oyster ‘spat’ settle onto cleared areas of seabed and are collected, young oysters spread out until grown large enough to be harvested (predators- crabs- removed)
What is oyster ‘spat’?
Planktonic larvae
Where are most shrimp farms?
Tropical seas: SE Asia and Latin America
What are the most important species of shrimp?
Tiger prawn
Pacific white shrimp
How much of the worlds mangrove has been destroyed for coastal shrimp farms?
10%
How many eggs will female shrimps lay in hatcheries?
Up to 500,000 each
How can ovary development and egg production be increased in shrimp aquaculture?
Eyestalk ablation where one or both eyestalks are broken off which simulates the low light levels which stimulate breeding because they are blind
What happens to the eggs produced by shrimp hatcheries?
Shrimp larvae are fed on algae and zooplankton, as they grow shrimp moved to outdoor lagoons up to 100 ha in size
What are the conditions like for extensive shrimp aquaculture systems?
Shrimps fed on plankton naturally produced in the lagoons
Are most salmon farms intensive or extensive?
intensive with the control of many factors to maximise productivity
What fish are chosen for salmon aquaculture? (characteristics)
chosen with desirable characteristics such as fast growth rate, shape, and brightly coloured scales
What happens to adult salmon in breeding condition? (aquaculture- gamates)
stripped of their roe (eggs) and milt (sperm)
These are allowed to mix and fertilisation take place
What happens to the fertilised eggs in salmon aquaculture?
raised in aerated freshwater tanks
Dead or diseased eggs are removed daily
When hatched young fish moved through series of tanks as grow being fed on fish meal pellets
What happens to the salmon in aquaculture after 12-18 months?
become ‘smolts’ and are ready to enter seawater tanks
continued to be fed on fish, and plant pellets until ready
At what weight will salmon be harvested in aquaculture?
3-5kg
Why does dissolved oxygen need to be controlled for salmon? (aquaculture)
sensitive to low dissolved oxygen (water temp not too high)
Where are most salmon farms? (temp)
Norway and Scotland where it is cold
How are salmon farms kept aerated?
water sprays and weirs
Why is water flow controlled in salmon farms?
kept fairly high to produce more muscular fish as swim against current
direction constant (circular tanks) reducing injuries
How are pest, disease and parasites controlled in salmon farms?
removing diseased fish and selective use of antibiotics and pesticides
What might be done to predators in salmon farms?
may be removed
Why are light levels controlled in salmon farms?
controlled to induce the smoltification of young fish as they mature
How is efficiency of the food chain in salmon farms controlled?
salmon are carnivores so fed fish meal pellets with low value fish (sandeels, herring, anchovy and sardines) similar to natural food
Food chain efficiency increased by adding food from lower trophic levels (plant foods + vegetable oils)
