Aquaculture is the breeding, rearing, and harvesting of fish, shellfish, algae, and other organisms in controlled water environments. It now accounts for 51 percent of all aquatic animal production worldwide, making it the primary source of farmed seafood on the planet. Global aquaculture production reached a record 130.9 million tonnes in 2021, of which 94.4 million tonnes were aquatic animals.
Marine vs. Freshwater Aquaculture
Aquaculture operates across two broad categories: marine and freshwater. Marine aquaculture, sometimes called mariculture, involves farming species that live in the ocean and estuaries. This includes salmon raised in coastal net pens, oysters grown on submerged racks, and seaweed cultivated on longlines. Freshwater aquaculture takes place inland, typically in constructed ponds, tanks, or recirculating systems, and produces species like catfish, trout, tilapia, and carp.
A third, smaller category involves brackish water, where fresh and salt water mix in coastal lagoons or river deltas. Shrimp farming in tropical regions often falls into this category. But the vast majority of global production breaks down along the marine and freshwater divide, with freshwater species dominating total volume.
What Gets Farmed
The species raised through aquaculture are more diverse than most people expect. Carp and related freshwater fish make up the single largest group, at 33.2 million tonnes per year, roughly 24 percent of all aquaculture production. Red and brown seaweeds together account for over 36 million tonnes, nearly 28 percent of the total. After that, the list includes marine shrimp and prawns (8.5 million tonnes), oysters (7.5 million tonnes), catfish (6.9 million tonnes), tilapia (6.8 million tonnes), clams and cockles (5.9 million tonnes), and salmon and trout (4.3 million tonnes).
This breakdown surprises many readers who associate aquaculture mainly with salmon. In reality, freshwater fish and seaweed dominate global output, largely driven by production in Asia. Salmon and trout, while high-profile in Western markets, represent only about 3 percent of world aquaculture volume.
Why Aquaculture Keeps Growing
Wild fisheries plateaued decades ago, with most major fish stocks either fully exploited or overexploited. As global demand for seafood continues to rise, aquaculture fills the gap. Of total aquatic animal production, 89 percent is used for direct human consumption, and global apparent consumption of aquatic animal foods reached 162.5 million tonnes in 2021.
The economics reflect this trajectory. The global aquaculture market was valued at $204 billion in 2020 and is projected to reach $262 billion by the end of 2026, growing at about 3.6 percent per year.
Farmed fish also convert feed into body mass more efficiently than most livestock. The standard measure for this, called the feed conversion ratio, compares the weight of feed given over an animal’s lifetime to the weight it gains. By this measure, aquaculture species and chickens perform similarly, and both outperform pigs and cattle by a significant margin. That said, when researchers look specifically at how much protein and calories end up in the final product, aquaculture’s advantage over livestock narrows. The efficiency gains are real but more nuanced than the raw numbers suggest.
Environmental Concerns
Aquaculture carries real environmental trade-offs, particularly in open-water systems. Fish waste and uneaten feed sink to the seafloor beneath net pens, depleting oxygen as they decompose. This can suppress native marine life and trigger algal blooms. Some commercial fisheries have raised concerns that these effluents affect the habitat and productivity of wild fish stocks.
Escaped farmed fish create another problem. Farmed salmon that escape into the wild compete with native populations for food and habitat, and interbreeding can weaken the genetic fitness of wild stocks. Disease transfer is a closely related concern. Sea lice, a parasite that thrives in the dense conditions of fish farms, can spread to wild salmon populations passing nearby. Other pathogens, including certain viruses and gill diseases, pose similar risks.
Chemical use adds another layer. Anti-fouling agents keep cages clean, various treatments target disease outbreaks, and feed ingredients can contain compounds that disperse into surrounding waters and harm other organisms. In land-based recirculating systems, standard antimicrobial treatments are often avoided because they destroy the beneficial bacteria needed to filter the water, so operators rely on more targeted alternatives.
Sustainable Approaches
One of the more promising strategies for reducing aquaculture’s environmental footprint is integrated multi-trophic aquaculture, or IMTA. The concept is straightforward: farm “fed” species like finfish or shrimp alongside species that naturally extract excess nutrients from the water. Shellfish filter organic particles, while seaweed and algae absorb dissolved nitrogen and phosphorus. Placing these species in close proximity creates a system where the waste from one organism becomes a resource for another, reducing the nutrient load that would otherwise accumulate in the surrounding environment.
Technology is also changing how farms operate. Researchers at the U.S. Department of Agriculture have developed an AI-powered computer vision system that monitors fish in real time using underwater cameras. The system detects individual fish with more than 85 percent precision, enabling farmers to track fish size, health, and population counts without physically handling the animals. This kind of non-invasive monitoring can catch disease early, optimize feeding schedules, and reduce both waste and stress on the fish.
How Aquaculture Differs From Wild Fishing
The core distinction is control. Wild-capture fishing removes animals from natural ecosystems, while aquaculture raises them in managed environments from egg or larval stage through harvest. This control allows farmers to select for growth rate, disease resistance, and other traits over successive generations, much like livestock breeding on land. It also means farmers can manage feeding, water quality, and stocking density in ways that wild fisheries cannot.
That control comes with responsibility. A wild fishery’s main sustainability question is whether you’re taking too many fish. In aquaculture, the questions multiply: what are you feeding the fish, what’s happening to the waste, how are you preventing disease, and what happens if animals escape. Both systems feed the world, but the challenges they pose are fundamentally different.