Denitrification was studied in anoxic batch cultures of a simulated fish processing wastewater at 37degreesC and pH 7.5, using a denitrifying enrichment culture from fishery wastewater. Different initial nitrate to biomass ratios (So/Xo) were used: nitrate and biomass varied from 7.5 to 94.7 mg NO3-N l(-1), and from 20 to 4300 mg volatile suspended solids l(-1), respectively. The specific maximum denitrification rate (r(m)) and the cell yield (Y-X/S) depended on the So/Xo ratio under anoxic conditions: r(m) increased from 1.2 to 1584 mg NO3-N g(-1) VSS h(-1) and Y-X/S decreased from 42 to 0.03 mg VSS mg(-1) NO3-N when So/Xo varied from 5.5 . 10(-3) to 9.3 mg NO3-N/mg VSS.