Nutrient Budget of Cage Fish Culture in a Lacustrine Environment: Towards Model Development for the Sustainable Development of Nile Tilapia (Oreochromis niloticus) Culture

Abstract

Carried out fundamentally in an open system, cage culture-derived nutrients can exacerbate the quality of the lacustrine environment. Information on nutrient loading from African inland waters is scarce, yet sustainable development of fish cage culture depends on it. This chapter reviews siting of fish cages, nutritional content, digestibility of fish feeds, and nutrient load in wastes of Nile tilapia in African inland waters. In addition, this chapter proposes a theoretical model for nutrient (nitrogen N and phosphorus P) budget in a Nile tilapia cage aquaculture farm to calculate the amount (kg) of N and P produced and released to the environment for each ton of fish produced basing on best and worst-case scenarios. The review shows that majority of the cages are sited nearshore and/or in shallow areas that could exacerbate environmental challenges. Poor digestibility of fish feeds, particularly P, raises concern due to the risk of eutrophication. The majority of the feeds used in African inland waters for cage fish culture recorded N deficiency in relation to P that could lead to poor retention, hence high nutrient loading into the environment. The theoretical model shows that about 46% of N and 39% of P from feed input are released into the environment for each tonne of tilapia produced. However, when the feed loss is high but at the same time the nutrient retention in fish is inefficient, 91% of N and 89% of P from feed input are discharged into the environment. Sensitivity analysis shows that nutrient loading from cage culture is very sensitive to feed loss, FCR and nutrient retention. The paper concludes with recommendations that need to be considered to minimise nutrient loading and its impact on the environment.