By the end of this lesson
- Describe the methods used in fish farming.
- Explain how each method increases yield.
- Evaluate the environmental effects of fish farming.
BIG QUESTION
How can thousands of fish be kept in a small space without most of them dying?
Each control the specification names prevents a different cause of poor growth or death in crowded conditions.
Water quality and waste
Water must be kept clean with a suitable temperature, pH and dissolved oxygen, often by pumping, filtering or aerating it. Fish waste and uneaten food produce ammonia and feed decomposers that use oxygen.
Waste products are removed by filtering or flowing water so they do not poison the fish or reduce oxygen.
Controlling predation
intraspecific predationAnimals killing and eating members of their own species, such as larger fish eating smaller fish. (fish eating their own species, such as larger fish eating smaller ones) is reduced by keeping fish of similar size and age together.
interspecific predationAnimals of one species killing and eating animals of a different species, such as birds or seals taking farmed fish. (by other species such as birds or seals) is reduced by nets and enclosures.
Disease control
Crowding helps disease and parasites spread. Farmers use clean water, quarantine, removal of sick fish, vaccines and sometimes antibiotics or pesticides.
Antibiotics and pesticides can enter surrounding water and can select for resistant microorganisms or parasites, so their use is controlled.
Feeding and selective breeding
High-protein food is given in controlled amounts and frequency, so fish grow quickly with little waste; overfeeding pollutes water.
selective breedingHumans choosing parents with desired characteristics to breed, then selecting the best offspring, over many generations. produces fish that grow faster, convert food efficiently, resist disease or are less aggressive. Restricting movement in enclosures also means less energy is used and more goes into growth.
Fish farming methods
The specification names each of these methods.
| Method | How it is done | Benefit for yield |
|---|---|---|
| Maintaining water quality | Filtering, aeration, monitoring. | Enough oxygen; no toxic build-up. |
| Controlling intraspecific predation | Separate fish by size/age. | Fewer fish eaten by larger ones. |
| Controlling interspecific predation | Nets and enclosures. | Fewer losses to birds and other predators. |
| Controlling disease | Vaccines, quarantine, treatments. | Fewer deaths in crowded conditions. |
| Removing waste | Flowing water, filters. | Prevents ammonia build-up and oxygen depletion. |
| Controlled feeding | Measured, high-protein food. | Fast growth with little waste. |
| Selective breeding | Breed fast-growing, docile fish. | Better growth and survival. |
Language that earns precision
- intraspecific predation
- Predation between members of the same species.
- interspecific predation
- Predation by a member of a different species.
- aquaculture
- Farming of fish and other aquatic organisms.
Common misconceptions
Claim: More food always means faster growth.
Correction: Uneaten food pollutes water and lowers oxygen as it decomposes.
Claim: Intraspecific and interspecific predation mean the same thing.
Correction: Intra- is within the same species; inter- is between different species.
Claim: Fish farming has no effect on wild fish.
Correction: Waste, escapes, disease and parasites can spread to wild populations.
Match the answer to the command word
Use the specification terms and give a reason for each method.
Balance protein production and reduced overfishing against pollution, disease spread and use of fishmeal.
Recall, apply, then justify
Describe how fish farmers control predation.
Hint
Within and between species.
Suggested marking points
- Keep fish of similar size/age together to reduce intraspecific predation.
- Use nets/enclosures to keep out other predators (interspecific predation).
Explain why water quality must be controlled in fish farms.
Hint
Oxygen, waste, disease.
Suggested marking points
- Fish need enough dissolved oxygen for respiration.
- Waste and uneaten food could build up and be toxic / be decomposed by bacteria that use oxygen.
- Poor water quality increases stress and disease.
Evaluate fish farming as a sustainable source of protein compared with catching wild fish.
Planning hint
Benefits and environmental costs.
What a strong design includes
- Farming reduces pressure on wild fish stocks.
- It produces a reliable supply of protein.
- Feed and conditions are controlled, so growth is efficient.
- Waste from farms can pollute surrounding water.
- Disease and parasites can spread to wild fish.
- Some farmed fish are fed fishmeal made from wild fish.
- Sustainability depends on farm management and feed source.