Aquaculture now supplies more of the world’s seafood than wild fishing does. It takes pressure off wild stocks, feeds millions and creates jobs. It also concentrates waste, disease and chemicals in one patch of coast — so the answer to “is it sustainable?” is never a simple yes.
📘 What you need to know
Aquaculture is the cultivation of aquatic organisms in controlled environments: ponds, tanks or ocean enclosures.
Farmed groups include fish, molluscs, crustaceans and aquatic plants such as seaweed and algae.
It has grown rapidly and is expected to keep growing as demand rises.
Benefits: additional food resources and economic development, plus reduced pressure on wild stocks.
Issues: habitat loss, pollution, disease spread, escaped species, and ethical concerns about welfare.
Operations must comply with international conservation legislation.
What gets farmed, and where
Aquaculture, also called fish farming or aquafarming, covers rearing, breeding and harvesting aquatic organisms for food, recreation or conservation. It happens in freshwater and marine settings alike.
Fish — salmon, tilapia, catfish, trout.
Molluscs — oysters, mussels, scallops, clams, and also octopus and squid.
Crustaceans — shrimp, prawns, lobsters, crabs.
Aquatic plants and algae — seaweeds such as nori, and spirulina.
Not all of these carry the same environmental cost. Farming mussels or seaweed adds no feed at all — the organisms filter or photosynthesise what they need. Farming salmon means feeding a predator, which is where most of the problems begin.
Why it keeps growing
Rising demand from a growing, urbanising, wealthier population.
Technology — better breeding, feed formulation and disease management raise output per pond.
Environmental pressure on the industry is pushing it towards cleaner practice, which makes expansion more acceptable.
Diversification into new species, including high-value fish and seaweed.
Policy support, as governments invest in aquaculture to improve food security and take pressure off wild stocks.
The key argument in its favour. Every tonne farmed is a tonne that does not have to be caught. That lets wild populations recover and the ecological balance of marine systems be restored — provided the farm itself is not doing damage elsewhere.
Feed: the hidden efficiency argument
Fish are cold-blooded and float, so they waste very little energy on staying warm or holding themselves up. That makes them remarkably efficient converters of feed into food.
This is the strongest environmental case for aquaculture. It weakens for carnivorous species like salmon, whose feed contains fishmeal made from wild fish that could have been eaten directly.
What goes wrong
Density is the root of it. Packing thousands of fish into one enclosure is what makes disease spread fast, waste concentrate and medicines necessary.
Issue
What happens
Habitat loss
Wetlands, mangroves and coastal areas are cleared or modified to build farms, damaging biodiversity, ecosystem functions and local livelihoods
Nutrient pollution
Uneaten feed and fish waste leach into surrounding water, causing eutrophication, algal blooms and oxygen depletion
Chemical pollution
Antifouling agents stop mussels and barnacles growing on the gear but leach into the water; feed additives can also affect quality
Antibiotics
Medicines used to control disease enter surrounding waters, harming organisms and contributing to antibiotic resistance
Disease spread
High density lets disease move quickly between farmed fish, and without biosecurity, pathogens reach wild populations too
Escaped species
Escapees compete and interbreed with wild fish, altering genetics and possibly spreading disease; genetically modified stock raises further concerns
Ethics and biorights
Intensive systems raise questions about confinement, stress, growth enhancers and the overall quality of life of farmed animals
A good evaluation separates farming herbivores and filter feeders from farming carnivores. Mussels and seaweed clean the water while they grow. Salmon need feeding, medicating and cleaning up after.
Worked examples
WORKED EXAMPLE 1
How much wild fish does a salmon farm use?
A farm produces 500 tonnes of salmon a year at a feed conversion ratio of 1.2. Fishmeal made from wild-caught fish makes up 20% of the feed. Calculate the mass of wild fish required.
Step 1: total feed needed500 × 1.2 = 600 tonnes of feedStep 2: the fishmeal share600 × 0.20 = 120 tonnes of wild fish120 tonnes of wild fish for 500 tonnes of salmonstill a net gain in food, but it shows why farming a predator only partly relieves pressure on wild stocks
WORKED EXAMPLE 2
Explain how a fish farm can cause an algal bloom [3]
Write a chained answer.
Link 1
Uneaten feed and fish waste release nitrates and phosphates into the surrounding water
Link 2
These nutrients cause rapid algal growth at the surface
Link 3
When the algae die, decomposers use up oxygen, causing oxygen depletionFish and invertebrates below the farm die offthis is eutrophication — name it, and link it to the water pollution topic if the question allows
WORKED EXAMPLE 3
Evaluate aquaculture as a solution to overfishing [7]
How to reach the top band.
Strengths
Reliable protein supply, reduced pressure on wild stocks, efficient feed conversion, jobs and income in coastal communities
Weaknesses
Habitat loss, eutrophication, antibiotics and antibiotic resistance, disease and escapees affecting wild fish
The important qualifier
Depends on the species farmed — filter feeders and seaweed have minimal impact, carnivorous fish need wild-caught feed
Ethical dimension
Welfare in intensive systems, and biorights arguments about confinement and stress
Judgement
A genuine part of the answer if well regulated and focused on lower trophic species; not a solution if it simply moves the damage from open sea to coastline
Species choice and regulation decide the verdictthat conditional judgement is what separates a 7 from a 4 here
💡 Exam tip
Define aquaculture as cultivation in a controlled environment, and mention freshwater and marine.
Give examples beyond fish: oysters, shrimp, seaweed.
Split issues into habitat, pollution, disease, escapees, ethics. Five headings, easy structure.
Use the species distinction — carnivorous versus filter-feeding — in every evaluation.
Mention compliance with international conservation legislation as part of responsible practice.
Link to the previous page: aquaculture only reduces pressure on wild stocks if it does not depend on wild-caught feed.
⚠ Common mix-up
Assuming farmed automatically means sustainable. It depends entirely on the species and the system.
Forgetting the feed. Carnivorous fish are fed on wild fish.
Confusing eutrophication with poisoning. The damage comes from oxygen depletion after the bloom dies.
Ignoring escapees. Genetic effects on wild populations are a distinct issue from disease.
Skipping the ethical angle. Welfare and biorights are explicitly in the syllabus.
Treating all aquaculture as marine. Much of it, including tilapia and carp, is freshwater.
Up next: Warming Seas and Ocean Acidification — the two pressures that no fishing regulation can hold back, and what they are doing to coral reefs.
Want this explained one-to-one?
Book a free session with an experienced IB ESS tutor and get your trickiest topics made simple.
