Aquaculture, the farming of aquatic organisms like fish, mollusks, and crustaceans in controlled freshwater or marine environments, is a rapidly growing sector of the global food system. Capture fisheries, in contrast, refers to harvesting wild aquatic populations from natural bodies of water. The relationship between these two methods is complex: aquaculture both relieves pressure on some wild stocks and creates new demands on others.
The Global Seafood Landscape
The contribution of farmed seafood has fundamentally reshaped the worldwide supply of aquatic food products over the last few decades. Production from capture fisheries has remained relatively stable since the 1990s, while aquaculture output has grown substantially. This expansion has positioned farmed seafood as the dominant source for human consumption globally.
In 2022, aquaculture production surpassed that of capture fisheries for the first time, providing 51% of the total aquatic animal production. For seafood destined only for direct human consumption, aquaculture’s share is 57% of the total volume. This rapid shift reflects aquaculture’s role in meeting the increasing global demand for protein.
Aquaculture as a Substitute for Capture Fisheries
The primary positive impact of aquaculture on worldwide seafood catch is the market substitution it provides for popular species. By supplying high volumes of certain fish, the industry lessens the need to increase fishing pressure on wild populations that might otherwise face overexploitation. This effect is particularly noticeable with species that are relatively easy to farm, such as tilapia, carp, and channel catfish, which are largely produced in freshwater pond systems.
Farmed Atlantic salmon is a prominent example of this substitution effect, as nearly all of the global supply is now sourced from aquaculture. If this immense demand had to be met by wild salmon stocks, those populations would likely be severely depleted or collapse. The cultivation of these species helps to stabilize the overall seafood market by providing a predictable, high-volume supply that is often more cost-effective than wild catch.
The availability of farmed fish also helps reverse the trend of “fishing down the food web,” where fishers target smaller, lower-trophic-level species as larger predatory fish stocks decline. By successfully farming high-trophic species like salmon, aquaculture supplies consumer demand for large carnivorous fish without relying solely on limited wild resources. This substitution mechanism is central to the argument that responsible aquaculture can be an instrument of marine conservation.
Dependency on Wild Stocks for Feed
A significant counterbalance to aquaculture’s relief on wild stocks is the industry’s continued reliance on capture fisheries for feed ingredients. Many highly valued farmed species, including Atlantic salmon, shrimp, and marine finfish, are carnivorous and require diets rich in protein and oils derived from marine sources. This demand translates into the capture of vast quantities of wild forage fish to produce Fishmeal and Fish Oil (FMFO).
Forage fish, such as anchovies, sardines, and menhaden, form the base of the marine food web. Their removal for feed production competes with natural predators like seabirds and larger wild fish, potentially disrupting entire ocean ecosystems.
Measuring Feed Dependency
The efficiency of this process is measured using the Fish-In:Fish-Out (FIFO) ratio, which tracks the amount of wild fish input required to produce one unit of farmed fish output. While the FIFO ratio for salmon has improved, it remains above 1:1, meaning that farming some carnivorous fish still requires harvesting more wild fish than is produced. Herbivorous species, like carp and tilapia, are net fish producers with FIFO ratios well below 1:1, but demand for high-value carnivorous species continues to pressure forage fish stocks.
The aquaculture sector is actively seeking alternatives to FMFO to reduce this dependency, including the use of plant-based proteins, insect meal, and algae. These innovations are gradually decreasing the inclusion rates of wild-caught ingredients in aquafeeds. However, the high nutritional quality and palatability of FMFO mean that a complete transition away from wild-caught ingredients remains a challenge, especially for species that require high levels of Omega-3 fatty acids.
Localized Ecological and Market Shifts
Beyond the global dynamics of supply and feed, aquaculture also creates localized impacts on wild fisheries and their surrounding environments. Ecological disruptions often occur due to the concentrated nature of fish farming operations. Open-net pens, for example, release concentrated waste, including uneaten feed and fish excrement, which can cause nutrient loading and localized pollution in coastal waters.
Ecological Impacts
The high density of fish in farming operations increases the risk of disease and parasite outbreaks, such as sea lice in salmon farms. These pathogens can transfer to nearby wild fish populations, weakening their health and reducing their survival rates. Furthermore, the escape of farmed fish, which are often genetically distinct from wild stocks, poses a threat of interbreeding that can dilute the genetic fitness of native populations.
In tropical regions, the development of coastal aquaculture, particularly for shrimp farming, has historically led to the destruction of sensitive habitats like mangrove forests. These vital ecosystems serve as nurseries for many wild fish and shellfish species, meaning their removal directly damages the productivity of local capture fisheries.
Economic Impacts
Economically, the high volume and stable, often lower, pricing of farmed seafood can depress the market value of wild-caught fish. This effect can undermine the economic viability of traditional local fishing communities, even when wild stocks are healthy.