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Aquaculture Environment Interactions

    AEI prepress abstract   -  DOI: https://doi.org/10.3354/aei00427

    Aquaculture carrying capacity of Nile tilapia Oreochromis niloticus and Nile crocodile Crocodylus niloticus in Lake Kariba, Zambia and Zimbabwe

    Kees te Velde*, Edwin Peeters, Marc Verdegem, John Beijer

    *Corresponding author:

    ABSTRACT: Increased aquaculture production can improve food and nutrition security and economic growth in developing countries, but comes with environmental risks. Recently, aquaculture has grown tremendously in Lake Kariba, which is located on the border of Zambia and Zimbabwe. This study calculated the carrying capacity of aquaculture production in Lake Kariba, using the Beveridge phosphorous balance model. It used data on lake-wide total-P concentrations and river flows and data from aquaculture farms and feed producers in the Lake Kariba area. The maximum permissible phosphorous load by aquaculture farms in Lake Kariba is 1.2 106 kg P yr-1. Average environmental phosphorous loss from Nile tilapia Oreochromis niloticus in Lake Kariba is 13.92 kg P t-1; and 92.5 kg P t-1 for Nile crocodile Crocodylus niloticus. Consequently, sustainable aquaculture carrying capacity in Lake Kariba is 86900 t yr-1 for O. niloticus and 13000 t yr-1 for C. niloticus. We expect aquaculture production in Lake Kariba to account for 71% of the total allowable aquaculture phosphorous load by 2028. Current growth plans of aquaculture farms seem acceptable, but further growth should be considered with caution. The total-P concentration is expected to increase to 28.5 mg m-3 by 2028, due to aquaculture growth. Developments in total-P concentration should be carefully monitored. In the future, our predictions should be compared to observed changes in order to validate the model. We also illustrate that companies can greatly improve the carrying capacity of the system by improving the feed conversion ratio, the efficiency of nutrient uptake and the processing of mortalities.