THE EFFECT OF TEMPERATURE DECREASE ON CARP CYPRINUS CARPIO L. CULTURE IN A TEMPERATE CLIMATE. PART II. ZOO- AND PHYTOPLANKTON DYNAMICS AND THE CHEMICAL COMPOSITION OF POND WATER
Maria A. Szumiec, Małgorzata Jakubas, Barbara Kolasa-Jamińska, Wanda Urbaniec-Brózda
Polish Academy of Sciences, Institute of Ichthyobiology and Aquaculture, Gołysz, Poland
ABSTRACT. Considerable decreases in temperature during the juvenile period of carp development directly affected the pond environment, its biotope and fish survival rates. High survival rates were observed when the temperature fell not earlier than ten days after stocking, while there was about a 25% decrease in dominating survival when it occurred earlier. The cumulative, unfavorable impact of temperature decrease on the pond biotope and fish appetite manifested itself in increased numbers of small Cladocera forms, decreased Copepoda and Rotatoria densities and an increase in the average number of phytoplankton species. When early cooling occurred, the increase of fish stock density in ponds caused an increase in small Cladocera forms due to the low fish pressure and an increase in the number of Cyanophyta and Chlorophyta in all seasons, which, in turn, was caused by the increasing productivity of the ponds. The chemical composition of the pond water was not deficient in nutritive salts. With only one exception, the fry survival rate was not threatened by the high concentration of non-ionized ammonia nitrogen.
Key word: CYPRINUS CARPIO, FRY SURVIVAL, WEATHER COOLING, TROPHIC CHAIN, POND ENVIRONMENT