The origin of particulate organic matter and the diet of tilapia from an estuarine ecosystem subjected to domestic wastewater discharge: fatty acid analysis approach

Abstract

The fatty acid composition of suspended particulate organic matter (POM) and tilapia (Oreochromis mossambicus) and potential sources of organic material in the Manko Estuary, Okinawa Island, Japan, were investigated to elucidate the origin of organic matter in suspended particulate matter and the contribution of these inputs to the diet of tilapia. Fatty acid fingerprints of POM revealed that diatoms, bacteria, and possible material input originating from domestic waste discharges contributed a major proportion of the organic matter pool in the estuary. The diet of tilapia is likely influenced by domestic waste-derived organic matter through a POM link. Because of their highly plastic feeding habits, tilapia may develop a feeding strategy of utilizing the most favorable food resources in the ecosystem. Tilapia likely does not prefer mangrove detritus as a food source as indicated by the absence of even-number long-chain fatty acids (LCFAs) in their tissues. Instead of mangrove detritus, tilapia preferentially utilized more palatable organic food sources in the water column, such as phytoplankton and its detrital matter. In addition to phytoplankton and bacterioplankton, the other dietary sources that contributed a minor fraction were possible green macroalgal materials and zooplankton.