Laboratory determination of a phosphorus leaching rate from trout (Onchorhynchus mykiss) feces

In order to reduce the impact that trout farm effluent can have on receiving water, it imperative to reduce the overall phosphorus (P) loading of these effluents. In response, the United States Environmental Protection Agency (US EPA) is issuing new effluent regulations for aquaculture. Therefore, efficient removal of P from effluent water is becoming increasingly important. The goal of this project was to determine the leaching rate of total and reactive P from trout feces under different water temperatures and water velocities immediately after evacuation. Scatter plots of the P load in the experimental containers over time were created for each fish/fecal sample and regression analysis was used to determine P leaching rates. Results from this study suggest that reactive phosphorus leaching rates are not affected by water velocities between 0.027 and 0.134 m/sec. However, at higher temperatures, reactive P leaches 1.92-mg PO₄/hr per g feces faster (F_1.52 = 4.6445, P = 0.0358) than at lower temperatures. Mean reactive phosphorus leaching rates were 2.88 ± 0.704 and 0.96 ± 0.581mg PO₄/hr/g feces, for the high and low temperatures, respectively. On the other hand, total P does not appear to be affected by either water velocity or temperature. Mean total P leaching rate is 4.50 ± 1.053 mg PO₄/hr per g feces. This study suggests that removal time of feces from the system is critical in reducing the overall P load in effluent.