Nitrogen and phosphorus waste in fish farming

Abstract

The current concern about the amount of residue generated from fish rearing suggests that this will be a decisive factor in the sustainability of fish farming in the coming years. Due to the great intensification of fish farming, the amount of residue deposited into the rearing tanks has increased significantly. Nitrogen (N) and phosphorus (P) are the main end-products of fish loading, and can affect not only the rearing water, but also the environment as a whole. The output of N and P metabolic wastes by fish was determined by numerous endogenous and exogenous factors such as genetics, life stage, size, rearing system, and diet. Ammonia is predominant type of N excreted, and high levels of ammonia excretion may be due to high protein intake or inadequately formulated diets which provide unbalanced protein synthesis. Phosphorus excretion, usually 69 - 86% of dietary P, is associated with the sources of origin, which are used in different ways by different species. The use of phytase in fish feeds is a good alternative which can help to reduce P waste. The diet balance should be standardized and the N and P excretion rates in several rearing systems (mainly the intensive farms) should be measured since a two- to three-fold decrease in the excretion of those pollutants in the fish culture systems could be attained.