Thirty three PCB congeners were analyzed in three size classes of seabass (Dicentrarchus labrax), from a semi-intensive fish farm, in food and in abiotic compartment. Water and suspended particulated matter (SPM) showed higher concentrations of lower chlorinated PCBs, whereas fish tissues and food showed higher concentrations of CB153 and CB138. In order to examine the influence of different inputs to seabass contamination, bioaccumulation factors (BAF), biota-suspended particulate matter bioaccumulation factors (BSMAF) and biomagnification factors (BMF) were calculated. In general, the log BAF and log BSMAF showed good correlations with log K(ow), for congeners with log K(ow)>6.1. In three fish size classes, PCB congeners with log K(ow)<6.1 were found at concentrations higher than what was expected based on the BAF calculated for the more hydrophobic congeners, suggesting a different contribution of sources. The application of a mass balance model for accumulation of some congeners in seabass estimated concentrations in fish 3- to 38-fold higher than the measured values, probably by overestimating gill absorption. The model was applied with other scenarios in order to maximize uptake from food, which may have a significant influence in accumulation, and not only from diet pellets. Its contribution to fish contamination for highly chlorinated PCBs may reach a maximum of 54-64%, and for lower chlorinated PCBs its contribution is lower than 20%. In this work it was proved that to reduce fish contamination the quality of the water should be controlled.