Influence of the date of autumn harvesting on the quality of discharged waters

The rearing of carp K2-3 in polyculture with a grass- carp, silver carp and European catfish was carried out within 1995- 1997, in six (1995-1996) or in seven (in 1997) variants of ponds differed in stocking densities as well as in kind of feed fed. The objective of the present paper was to verify if the change of harvest date from September into November can affect the quality of discharged waters. Estimation of discharged water quality was made on the basis of following chemical factors: dissolved oxygen, water pH, total suspended matter, chemical oxygen demand CODMn, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen and phosphates. The change of harvest date for 40 days improved markedly the quality of discharged water.