Bioturbation-induced phosphorous release from an insoluble phosphate source

The influence of bioturbation caused by common carp fry in 5 L jars (5 L each) in the laboratory and in 150 L outdoor vats in increasing the fertilizer value of phosphate rock was evaluated. Soluble reactive phosphate (SRP) was determined to quantify the effects of bioturbation, fish excrements and soil. The level of SRP was always lowest in the control series. Introduction of common carp fry resulted in a net increase of 0.09–0.10 mg L−1 of SRP attributable to the effect of fish excrement. Bioturbation caused by common carp resulted in a 64.8–90% influx of phosphate from bottom soil in the presence of phosphate rock but only about 6.3–7.2% in the absence of phosphate rock. The bioturbation that occurred in these treatments resulted in a significant release of phosphorous into the overlying water from the apatite source. The results confirm the benefits of the application of environmentally friendly phosphate rock in fish farming ponds at low cost.