Seasonal tanks, which dry-up completely during August-October every year are ver^ productive and have a great potential for fish culture in Sri Lanka. Fish farming communitiejs produced fmgerlings of Oreochormis niloticus, Labeo dussumieri and Cyprinus carpio in back-yard ponds and net cages installed in perennial reservoirs in order to stock in seasonajl tanks. 1
Fourteen seasonal tanks (0.1-1.4 ha in size) in Hambantota District in the south-eastern par: of Sri Lanka were stocked with O. niloticus: L. dussumieri'. and C. carpio. The ratio of fish (O. niloticus. L. dussumieri. C. carpio) used for stocking were, 1:4:2, 4:7:3, 2:6:3, 5:4:1 and 7:4:1 in different seasonal tanks. For each ratios, except for 2:6:3 (in 4 tanks), two seasona. tanks were used. The initial stocking sizes were 5-9 cm for O. niloticus, 3-5 cm foriZL dussumieri and 4-7 for C. carpio.
Physio-chemical parameters, i.e. pH, temperature, dissolved oxygen, conductivity, alkalinitjy, Secchi disc depth and salinity were recorded at weekly intervals.
From the data obtained from the harvesting it appears that O. niloticus and. C. carpio show better growth than L. dussumieri in these small sized seasonal tanks. The harvesting carriejd out in early August 2000. Further analyses on survival rates of the three species, relationships between limnological parameters and yield will be determined thereafter.