An energy computation of a serially-connected, sewage-fed fish pond system was made. The annual solar radiation was 4456.2 MJ/m(2). The synthetic efficiency of solar radiation to different fish ponds varied from 0.46 to 1.24%. The total energy input and phytoplankton production in ponds ranged from 11328 to 29082.2 MJ/y and 8.89 to 23.60 kg/m(2)/y, respectively. The gross conversion efficiencies of total, photosynthetic, biological and biological-industrial energy varied from 0.58 to 3.3%, 1.5 to 6%, 0.95 to 11.1% and 0.92 to 10%, respectively, in different fish ponds. The gross energy consumption for the production of fish varied from 116.9 to 732.5, 68.9 to 275.8, 34.9 to 443.7 and 38.9 to 456.8 MJ/kg fish for total solar; biological and biological-industrial energy, respectively, in different ponds. The selection of fish species and maintenance of optimum physico-chemical and biological parameters are suggested to improve the energy transformation in sewage-fed fish ponds.