It has been observed that the favorable economic impacts of tilapia eroded over time primarily due to its invasive nature. A number of causes can be identified in this regard. First, it has been noticed that due to high proliferation rate, the size of tilapia has decreased over time. Since the unit price of fish increases with the size of fish, the decrease in size has reduced profitability of tilapia fishing.

However, some argues that this is not due to stunning of tilapia, but due to the overfishing. Second, tilapia was found to hamper the bio-diversity of water reservoirs. It was evident that when tilapia is present, availability of food for indigenous and non-indigenous fish species reduces. This can make some of such spices at the risk of extinction. Third, tilapia increases turbidity of water which prevents transmission of sunlight to the water body. This makes other planktons difficult to grow. The end results is tilapia dominates in inland reservoirs at the cost of other fish and planktons species. Forth, there is an indirect effect on human health associated with consumption of tilapia due to the risk of passing heavy metals along the food supply chain. Fifth, with the improvement in fish marketing system, relative prices of costal fish has reduced over time lowering the importance attributed to tilapia as the key source of protein to rural communities.
As a remedial action it has been proposed to control populations of tilapia in reservoirs. It has already been recommended to use male tilapia when stocking is being done.

However, according to our knowledge, no scientific study has been conducted to assess costs and benefits of introduction of tilapia to inland waters in Sri Lanka and measures introduced by the scientific community to manage the spread of the same. Such an investigation is timely as social cost and benefit estimates are needed to shed lights on making recommendations on optimal tilapia populations in water bodies.

Research questions/objectives

Main objective: To assess economic impacts of the spread and management of tilapia in perennial tanks in Anuradhapura district in Sri Lanka.

Specific objectives:

  1. To document contribution of inland fisheries (in general) and tilapia (in particular) in improving rural incomes and alleviating protein malnutrition in Sri Lanka;
  2. To describe the extent to which rural communities in Anuradhapura district are benefited by tilapia fishing
  3. To describe the other beneficial and adverse outcomes, both ecological and social, associated with tilapia farming in perennial tanks paying special attention to eco-system services;
  4. To quantify the social costs and benefits associated with tilapia fishing in perennial tanks paying special attention to value of tilapia harvest and degradation of eco-system services provided by the perennial tanks;
  5. To document the key features of technical solutions proposed by the scientists to manage tilapia in Sri Lanka and to numerically simulate social benefits and costs associated with proposed technical solutions.