Anaerobic treatment of wastewater from a selected seafood processing plant was conducted at organic loading rates (OLR) ranging from 0.3 to 1.8 kg chemical oxygen demand (COD)/m(3).day and hydraulic retention times (HRT) ranging from 36 to 6 days. COD reduction decreased with increasing OLR. More than 75% COD reduction could be maintained up to an OLR of about 1 kg COD/m(3).day with an HRT of 11 days. An OLR of 1.3 kg COD/m(3).day corresponding to an HRT of 6.6 days gave maximal biogas productivity of 1.5 m(3)/m(3).day or 1.3 m(3) biogas/kg COD with a 65% COD reduction. If the HRT was kept constant at 11 days, an OLR of 1.3 kg COD/m(3).day achieved maximal biogas productivity (1.1 m(3)/m(3).day) and yield (0.75 m(3)/kg COD) and a 60% COD reduction for treatment of tuna condensate.