Waste loading into a regulated stream from land-based trout farms

This study aimed to characterize the effluents of 3 flow-through farms with annual production rates of 250, 750 and 2500 t yr(-1) at a site with a total annual production of 4400 t yr(-1). We determined the nutrient loads from rainbow trout Oncorhynchus mykiss farms using nutritional and hydro logical mass-balance models and estimated the fluxes into a regulated stream and into the Mediterranean Sea between March 2008 and February 2009. When compared with the influent, farming activity significantly decreased dissolved oxygen (p < 0.001) and increased biochemical oxygen demand, suspended solids, and nitrogen and phosphorus fractions (p < 0.05) in the effluents. The load predictions of 44.3 kg N and 8.4 kg P t(-1) of fish produced by the nutritional method were close to the measured values of 43.9 kg N and 8.8 kg P t(-1) of fish produced. The load prediction for suspended solids was the same as the measured value of 278 kg t(-1) of fish produced. The predictions were well correlated with measurements for suspended solids and for total nitrogen and phosphorus. The estimated annual mass fluxes of nitrogen and phosphorus from trout farms at the site into the eastern Mediterranean Sea were 125 to 127 and 24 to 25 t yr(-1), respectively. The nutritional mass-balance model may be the method of choice as a decision tool for the environmental impact assessment of land-based aquaculture because of its simplicity and easy application.