Short answers, pulled from the story.
Aquaculture is the controlled cultivation, or farming, of aquatic organisms such as fish, crustaceans, mollusks, algae, and aquatic plants. It differs from commercial fishing, which is the harvesting of wild fish, because aquaculture rears species under controlled or semi-natural conditions with intervention such as stocking, feeding, and protection from predators.
Global aquaculture output was over 120 million tonnes valued at 274 billion US dollars in 2019, rising to 130.9 million tonnes valued at 312.8 billion US dollars in 2022. There are documented issues with the reliability of the reported figures.
The most important fish species used in fish farming worldwide are, in order, carp, salmon, tilapia, and catfish. Fish farming, which raises fish in tanks, ponds, or ocean enclosures, is the most common form of aquaculture.
Products from several kilograms of wild fish are used to produce one kilogram of farmed salmon, measured as the fish-in-fish-out ratio. In 1995 salmon had a ratio of 7.5, meaning 7.5 kilograms of wild fish feed per kilogram of salmon, and by 2006 the ratio had fallen to 4.9.
A salmon farm with 200,000 fish discharges more fecal waste than a city of 60,000 people, and about 20 percent of mangrove forests have been destroyed since 1980 partly due to shrimp farming. Whole-lake experiments in Ontario, Canada, showed cage farming raised ammonium and phosphorus and quadrupled phytoplankton biomass annually.
China reports an aquaculture output double that of the rest of the world combined, and in 2001 scientists Reg Watson and Daniel Pauly raised concerns it had over-reported its wild fishery catch in the 1990s. The Food and Agriculture Organization accepted there were reliability issues and for a period treated China's data separately from the rest of the world.
Shellfish aquaculture adds filter feeding capacity, with a single oyster able to filter 15 gallons of water a day while removing nitrogen and other nutrients. Seaweed farming is a carbon negative crop that the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommended for further research attention as a climate mitigation tactic.