5.16 - Aquaculture

Learning Objectives

I. Aquaculture Defined

• Definition: Aquaculture is basically agriculture, but in the water. It means raising aquatic species like fish, crabs, or seaweed to use as food.

• Aquaculture species are generally raised in cages or some kind of underwater enclosure.

• Global context: In 2024, farmed aquatic animals passed 100 million metric tons for the first time, more than the roughly 92 million metric tons of wild-caught aquatic animals (FAO, 2026).

II. Benefits of Aquaculture

1. Efficiency: It takes up a very small amount of water space and fuel compared to deep-sea fishing or other methods that pull fish from wild populations.

2. Avoids fishery collapse: It sidesteps the risk of fishery collapse (a 90% or greater decline in a fish population) because fish are bred and raised rather than caught from wild ocean populations.

3. Land use efficiency: Ocean net pens take up no land, and even pond farms use much less land per kilogram of protein than beef, pork, or chicken. Fish are also efficient at turning feed into meat, since they're cold-blooded and the water holds up their bodies, so they burn less energy than land animals.

4. Sustainability potential: Aquaculture can be done sustainably by using fish waste as a nutrient input for invertebrates like crabs, which effectively clean up that waste.

III. Drawbacks of Aquaculture

1. Waste concentration and water quality: Just like CAFOs on land, packing animals in at high density means a very high concentration of their waste. That can lead to:
• Low oxygen under the pens: leftover feed and feces sink, and bacteria use up oxygen as they decompose them. The waste-filled water flows out into the surrounding area.
• Eutrophication from all the excess nitrogen in the waste.

2. Disease spread: High density means a high probability of disease outbreak. Since the fish are in cages in open water, disease can easily reach nearby wild populations and spread through them.
• Real example: Sea lice (small parasites) multiply in crowded salmon farms and spread to young wild salmon swimming past the pens on their way out to sea, in places like Norway and British Columbia.

3. Escape of non-native species: The species being grown may be non-native or genetically modified. If they escape the enclosure, they may breed with wild populations or become invasive.
• Real example: In 2017, a net pen holding non-native Atlantic salmon collapsed near Cypress Island, Washington, and released roughly 250,000 fish into Puget Sound. In 2018, Washington passed a law phasing out farming of non-native fish in its waters.

4. Antibiotic contamination: Because the fish are packed so densely, antibiotics are often used to prevent disease. The antibiotics pass through the fish and out into the surrounding water, where they can help bacteria evolve antibiotic resistance.

5. Pressure on wild fish: Farmed carnivorous species like salmon and shrimp are fed fishmeal and fish oil made from wild-caught forage fish like anchovies, so aquaculture doesn't fully take the pressure off wild fish populations.

6. Habitat loss: In tropical countries, shrimp farms have cleared large areas of coastal mangrove forests (8.4).