Fisheries enhancement involves activities designed to increase the size and numbers of fish available in inland waters. It is also used to conserve endangered species and to raise the productivity of particularly valuable fish stocks. Fisheries enhancement has become quite common throughout the world, especially in places where non-fishing activities have threatened or eliminated important species of fish or where simply more fish are desired.
There are several ways to enhance a fishery. Stocking, or adding fish to a body of water, can be done to increase supplies of fish. Stocking is also done to encourage the growth of favored species or to introduce new species in waters. When the fish that is being stocked in inland fisheries comes from an aquaculture hatchery, the practice is called culture-based fisheries. In some areas, juvenile or small adult fish are taken out of their natural waters and reared in fish ponds to which nutrients and fish food are added. The fish in these ponds are "farmed". It is possible to alter the fish genetically (for example, by choosing the best fish to breed or by manipulating their chromosomes) in order for example, to promote better growth or resistance to disease. Later, the farmed fish are harvested for food or released back into their native waters.
Natural fish populations can also be improved through traditional knowledge and practices such as placing brush or plants in water bodies. These practices are complex and usually based on established and accepted community values and beliefs. These practices are regarded as aquaculture if the fish that is stocked is accepted as owned by an individual or a group (i.e., the "growers") during the grow-out period until harvested (that is, the period that it takes for the fish to reach maturity ready for harvest). All these practices are parts of aquatic production systems in many parts of the world and they support food security and rural livelihoods.
In addition to being stocked in natural waters or in aquaculture ponds, some species of fish are used for the ornamental fish trade. Rather than being used for food, these fish are sold for display, such as you see in gardens or aquariums.
Healthy population of fish lead to better diets and increased incomes for people living in fishing communities. However, enhancement activities can negatively affect natural fish supplies. Sometimes as new species are introduced, the original (native) species die out. Most conservation efforts in areas where the environment has been changed by human activities concentrate on re-establishing "sustainability" of the resources (that is, the ability to use the resources for a long period of time without causing damage to them). Studies should be done on enhancement activities, and the introduction of inappropriate species should be avoided if the studies indicate that these activities are harmful.
Most of the world's inland waters will never be returned to the way they were originally. When a dam is constructed, wetlands are drained, river channels are altered, lakes are polluted or a new species of fish is introduced into a body of water, it is difficult to re-establish the original conditions even when the harmful activity stops. Some natural features of the area may need to be rehabilitated. This means that an attempt is made to restore the waters to something like its natural state in which fish can thrive.
When a river has been artificially straightened by an industrial or navigation project, a series of corrective steps can be taken. These steps range from such activities as adding boulders and special vegetation along the river bank creating islands in the river. In areas where fish migrate upstream or downstream but are prevented from doing so by a dam or some other structure, fish-passes, locks, and bypass channels can be constructed to allow the fish to swim over or around the structure. If nearby flood plains in which fish thrive and spawn are permanently cut off from a river channel, artificial structures like levees can be removed to allow the river to flood and to let the fish move between river and floodplain.
Likewise, water quality can be improved in polluted rivers and lakes. Pollution (such as wastes from factories) which threatens fish stocks can be treated by constructing waste water treatment plants.
Apart from developing fisheries for food, many countries now use some of their inland waters for recreational purposes. While individuals may fish for food in a recreational area, the fish caught are reserved for personal use rather than commercial sale. Recreational fishing can provide significant economic and financial benefits to inland water communities. Recreational fishers spend money for licenses and access to the area, gear, transport and accommodation. The people who gain financially are the resource owners (who may charge a fishing fee), employees and guides in the fishery area, boat owners, and people who provide travel and accommodation services.
There is unlikely to be a commercial food fishery and a recreational fishery in the same place. Since recreational fisheries may bring more money into an area, they can push out fisheries that exist to provide food. To avoid such conflicts, countries should recognize the potential both of commercial enhancement fisheries and recreational fishing.