Fish are important because they sit at the intersection of human nutrition, global food security, and the health of aquatic ecosystems. They provide essential nutrients that are difficult to get from other foods, support the livelihoods of tens of millions of people, and play roles in lakes, rivers, and oceans that keep those systems functioning. Here’s a closer look at each of those dimensions.
A Unique Package of Nutrients
Fish are one of the few food groups that deliver meaningful amounts of omega-3 fatty acids, vitamin D, iodine, selenium, and vitamin B12 in a single serving. No other category of food covers all of these at once. That matters because several of these nutrients are chronically under-consumed, and some are nearly impossible to get in adequate amounts from land-based foods alone.
The omega-3 fats in fish (EPA and DHA) reduce the heart’s susceptibility to dangerous rhythm problems, lower triglyceride levels, and decrease blood pressure. DHA is also concentrated in the brain and retina, and diets high in these fats are associated with a lower risk of cognitive decline and Alzheimer’s disease. Your body can convert plant-based omega-3s (from flaxseed or walnuts) into EPA and DHA, but the conversion rate is low, making fish the most efficient dietary source.
Vitamin D is another standout. Foods naturally rich in vitamin D are rare. Eggs and liver contain some, but fish are the best whole-food source by a wide margin. Herring delivers about 17 micrograms per 100 grams of edible flesh, salmon about 15, and mackerel about 10. For context, most adults need 15 to 20 micrograms a day. A single serving of fatty fish can cover most or all of that requirement, which is significant given that vitamin D is critical for calcium absorption and bone health.
Marine fish and shellfish are also among the only reliable natural sources of iodine, a trace element essential for thyroid function. Iodine deficiency remains the leading preventable cause of brain disorders worldwide. Cod contains about 160 micrograms of iodine per 100 grams, mussels around 365, and mackerel about 64. Freshwater fish, notably, do not provide appreciable iodine. Selenium, which supports thyroid enzyme activity and antioxidant defenses, is also well-supplied by seafood: tuna delivers roughly 56 micrograms per 100 grams, and oysters about 55.
A Pillar of Global Food Security
Fish feed a staggering number of people. According to FAO data, aquatic foods contributed at least 20 percent of all animal protein consumed by 3.2 billion people in 2021. In many coastal and island nations, that share is far higher, making fish not just a dietary preference but a survival staple.
The industry behind that food supply is equally massive. In 2022, an estimated 61.8 million people worked in commercial fisheries and aquaculture worldwide. Beyond the commercial sector, subsistence fishing engages roughly 53 million additional people, nearly half of whom (about 23.8 million) are women. For communities with limited arable land or livestock, fishing is often the primary source of both income and nutrition. Losing access to healthy fish populations would remove the main protein source and economic engine for hundreds of millions of people simultaneously.
How Fish Keep Ecosystems Running
Fish do more than occupy a link in the food chain. They actively move nutrients through ecosystems in ways that boost the productivity of the waters they live in. In lakes, for example, certain species feed on organic material buried in bottom sediments and then excrete those nutrients back into open water, where they fuel the growth of phytoplankton (the microscopic algae at the base of aquatic food webs). Studies in productive lakes surrounded by agricultural land found that this nutrient recycling by fish supported an average of 51 percent of all phytoplankton production, with some lakes reaching as high as 67 percent. Even in less productive, forested watersheds, fish-driven nutrient cycling accounted for 14 to 23 percent of primary production.
In ocean environments, the role shifts but remains critical. On coral reefs, herbivorous fish like parrotfish and surgeonfish graze on algae that would otherwise smother coral. Large parrotfish use their powerful beaks to scrape algae off reef surfaces, clearing space for new corals to settle and grow. When grazer populations decline from overfishing or habitat loss, thick algae mats take over, reducing coral growth rates and blocking the settlement of young corals. Since coral reefs support roughly a quarter of all marine species despite covering less than one percent of the ocean floor, the loss of these grazing fish cascades far beyond the reef itself.
Living Sensors of Water Quality
Fish also serve as biological indicators of environmental health. Analyzing water or sediment samples gives only a snapshot of conditions at a single moment. Fish, by contrast, accumulate trace elements over their entire lifespan, providing an integrated picture of pollution exposure over months or years. Species that stay in one area of a lake or river are especially useful because their tissue concentrations reflect local conditions rather than averaged-out readings from migratory routes.
Researchers have found that fish handle different types of contaminants in distinct, readable ways. Essential minerals like copper and chromium are tightly regulated by the fish’s own biology, so their levels in tissue stay relatively constant regardless of water conditions. Non-essential metals like cadmium, lead, and silver, however, accumulate in proportion to environmental exposure. This makes fish tissue a reliable gauge of toxic metal pollution in a body of water, often catching contamination problems that periodic water sampling would miss.
This bioindicator role has practical consequences. Fisheries managers and environmental agencies use fish health surveys to decide when waterways need intervention, which pollutants are present, and whether cleanup efforts are working. A declining or unhealthy fish population is frequently the first clear signal that something has gone wrong in an aquatic ecosystem.
What Happens When Fish Disappear
The importance of fish becomes most visible when they’re removed. Overfished coral reefs shift from diverse coral communities to monotonous algae fields. Lakes lose the nutrient cycling that supports their food webs from the bottom up. Coastal communities lose their primary protein source and economic base. And monitoring systems lose one of their most reliable long-term indicators of water quality.
Fish occupy a rare position where ecological function, human nutrition, and economic livelihood all converge in a single group of organisms. Protecting fish populations isn’t just about preserving biodiversity in the abstract. It’s about maintaining nutrient cycles that support entire ecosystems, safeguarding a food source that billions of people depend on, and keeping a natural early-warning system for environmental contamination intact.