INVESTIGATION OF DUCKS INFLUENCE UPON NUTRIENTS IN CARP PONDS BY MEANS OF RDA (REDUNDANCY ANALYSIS)

摘要

Integrated breeding of fish and ducks in fish ponds during the course of three years has been investigated (2000-2002). The polyculture applied has included carp (Cyprinus carpio, Linn), bighead carp (Aristichthys nobilis Rich.) and grass carp (Ctenopharingodon idella Val.). The grass carp has been absent from the composition of the polyculture used in 2001. Some of the ponds has been used as control, while in the remaining, a definite number of ducks have been grown (140-350 numbers per ha), by one,two or three runs (series) per year, for a period of 15-52 days each, within the interval May-September. The final result of ducks' and of the other variable influence upon the nutrient concentrations of the aquatic environment by using the RDA (redundancy analysis) at different degrees has been determined in this paper. The overgrowing of ponds with macrophytes and the redundancy with ducks have been the most significant factors, which have influenced upon the nutrients. The differences among nutrientconcentrations in the control ponds (DuckO) and those with 1,2 and 3 levels of loading (P=0.01 for the 1 level and 0.005 for the second and third), as well as those with the 1 and 3 (P=0.005) levels, have been significant. The differences between the ponds with the 1 and 2 levels, as well as those with 2 and 3 levels have been not significant (P=0.06 and P=0.08).