Inland Fisheries

9.1.5.2 Deliberate Introductions

Several reasons are usually offered for introducing a new species into a lake or river:

1. Create new fisheries that are more resistant to fishing pressure or have greater market value than native fish. New species are introduced into recreational fisheries to improve the variety available to the anglers or to insert a species of particular trophy or sporting value into an area.
2. Fill a “vacant trophic niche” where existing species do not fully use the trophic and spatial resources available
3. Control pests – several species have been introduced in an effort to biologically control pests and vectors of human disease.
4. Control water quality – where suitable phytoplankton eating species are lacking to remove excessive algae in eutrophic systems
5. Develop aquaculture – this remains one of the main motives for the movement of species around the world. Many species have been introduced for culture. Escapes from aquaculture installations have contributed to many successful introductions into the wild.

The major factors that lead to consider introduction of exotic fishes in the aquaculture field include:

• Growth of indigenous species was not up to the mark
• Indian Major Carps do not breed in confined waters
• Natural recruitment of carp species failed at times due to monsoonal disturbances
• Stocking of reservoirs could only be done by collecting seeds from the wild
• With the available fish community the trophic niches could not be utilised fully.
• Improve sport fishery - Introduction of alien fish for recreational fishing has resulted in extirpation of many native fishes around the world. The adverse impacts of salmonid sport fishes like brown trout on multiple ecological levels have been well documented.
• Fulfil aesthetic and other reasons – ornamental species are now widely distributed throughout the tropical world through escapes from rearing installations and aquaria. Some species have also been introduced for particular religious or cultural reasons.