Freshwater aquaculture

Unit 5 - Impact of exotic (Introduced) species

5.2. Adverse impacts of Introductions
When introduced, species escape from the farm; or, when they are deliberately introduced into natural ecosystems such as lakes, reservoirs and streams, they have potential to cause adverse impacts on the ecosystem and biodiversity into which they are introduced. A few of the following adverse impacts are listed below:

• Depletion of biodiversity
• Endangering native species
• Compete for food and space with native species.
• Introduce new parasites and diseases
• Genetically interact with local species and contaminate the gene pool of the native species.
• Degrade ecosystems
• Have adverse impacts on the socio – economic aspects of human life.

The introduced species will have more adverse impact on the freshwater because; although freshwaters represent only 0.1% of the earth’s water it contains 40% of the total fishes on the earth. Out of these, 20% of the fauna is already extinct or are at the verge of extinction. Introduction will further aggregate the situation and may lead to extinction of more species.

Case study -1
In Lake Victoria of Africa there were about 300 endemic species of fish. 99% of the population (8 million people) of Kenya, Uganda and Tanzania depended on Lake Victoria for their lively hoods and food.
The Nile perch Lates niloticus was introduced into this lake with the intention of enhancing fish production. Majority of the endemic fish became extinct, affecting the livelihood of the 8 million populations.

Case study - 2
Introductions within the country into a different habitat can also cause severe adverse effects on the local flora and fauna. Grass carp a native of China was introduced to Danghulake in China. It resulted in complete destruction of macrophytes leading to plankton blooms. Big head carp and silver carp, also natives of China were introduced to control the resulting algal blooms. Algal blooms were not completely controlled, but the number of benthic species came down to 26 from the original 113 and zooplankton from 203 to 71. The drinking water supply was completely affected.