Fish stocking is the practice of releasing fish that are artificially raised in a hatchery into a natural body of water (river, lake, or ocean), to supplement existing wild populations or to create a new population where previously none exists. Stocking may be done for the benefit of commercial, recreational or tribal heritage fishing, but may also be done for ecological conservation to restore or increase the population of threatened/endangered fish species that is pressured by prior overfishing, habitat destruction, and/or competition from invasive species.

Fish stocking may be conducted by governmental fisheries management agencies, non-profit organizations, and voluntary associations in public waters, or by for-profit NGOs, clubs and commercial enterprises in privately owned waters. When in public waters, fish stocking creates a common-pool resource which is rivalrous in nature but non-excludable. Thus, on public grounds, all can enjoy the benefits of fishing so long as fish continue to be stocked.

Fish stocking is a practice that dates back hundreds of years. According to biologist Edwin Pister, widespread trout stocking in the United States dates back to the 1800s. For the first hundred years of stocking, the location and number of fish introduced was not well recorded; the singular goal of stocking was to enhance sport fishing regardless of ecological ramifications such as erosion of biodiversity. As Pister states, "When trout planting was first implemented, the nation was gripped with a highly utilitarian resource management ethic that placed short-term human interests above virtually any other consideration". Recently, the U.S. Fish and Wildlife Service along with state fishery branches have done a better job of recording exactly what species of fish are stocked at any given location. This began in the 1960s when research suggested the negative impacts of fish stocking on the ecological complexity of other life forms. The Wilderness Act of 1964 also opened the public's eyes to the impact stocking has on other organisms. Thus, fish stocking is now the subject of much debate as there are various costs and benefits associated with the practice.

In the United States, stocking non-native fish for sport and food was just beginning in 1871 when the US Fish Commission was established. The head of the new agency, Spencer Fullerton Baird, was tasked to research "the decrease of the food fishes of the seacoasts and the lakes of the United States and to suggest remedial measures". Baird made his headquarters at Woods Hole on Cape Cod, Massachusetts. There, his team of scientists and researchers conducted studies on striped bass, blue fish and many other commercial and sport fish. They compiled their research into a 255-page report on United States fish resources. Congress granted the team $15,000 to develop food fish stocks, and non-native fish such as rainbow trout, salmon, striped bass and carp were subsequently introduced successfully into United States lakes and rivers. In the early years, fish were stocked by sports clubs and private citizens. Today, state fish and wildlife agencies along with hatcheries are responsible for distributing fish. And until recently, their goal was to plant as many fish as possible into as many bodies of water as possible. Now, with knowledge of the detrimental effects fish stocking has on invertebrate and amphibian populations, it is conducted much more selectively.

Today, much more thought is put into introducing non-native species as they can severely damage the populations of fragile natives; practices lean more towards sustainability. Stocking is used to restore native species to waters where they have been overfished or can no longer breed. "Give and take" stocking practices are those where fish are stocked only to be fished and then restocked. In response, most states have adopted regulations that prohibit fish stocking in areas that may damage aquatic life or ecosystem diversity, and encourage stocking in bodies of water where no harm will result from doing so. Trout Unlimited has a policy, for example, that states "where a body of scientific evidence shows that stocking in historically non-salmonid waters adversely affects native biodiversity, such stocking should cease." While many organizations remain focused solely on providing quality fishing opportunities, policies and attitudes are shifting toward resource integrity and protection.

In Pennsylvania alone, the PA Fish & Boat Commission is scheduled to stock 4,398,227 trout (brook, brown, and rainbows) into its streams and lakes in 2019. Also in 2019, Lake Ontario, one of the five Great Lakes, is projected to receive 2,767,660 stocked salmon and trout. According to data by state agencies, in 2004 roughly 1.7 billion fish were stocked across the United States. With 104 different species of fish stocked, a total of 43.65 million pounds of fish were released, primarily in the Western states. In the US, common species that are currently stocked for sport include trout, bass, salmon, muskellunge, walleye, and several species of panfish.

Before being released into rivers, lakes, ponds, and occasionally oceans across the country, fish are raised in a fish hatchery. Just like humans have a demand for groceries, anglers have a demand for fish. When the supply is running low in a given body of water, fish are transported from hatcheries in a large water tank or airplane to their respective locations. The costs associated with stocking are typically covered by angler associations, commercial fishermen, state fish and game agencies, and at times government subsidies; today, most stocking is conducted by state fish and game departments.

Radinger et al., 2023 conducted large-scale experiments across 20 lakes, to systematically test the effects of stocking fish compared to habitat-based interventions (i.e. creating shallow zones and adding coarse woody habitats). Over a period of six years, they closely monitored the fish population response in each lake. The study revealed that species-focused fish stocking was completely unsuccessful and demonstrated the potential for ecosystem-based management to better meet conservation goals.