Croatian Journal of Fisheries (Mar 1994)
INFLUENCE OF FERTILIZATION ON THE DEVELOP MENT OF PHYTOPLANKTON ON CARP FISH FARMS
Abstract
A comparative investigation on the effect of fowl fertilizer (4800 kg. ha-1) and mineral fertilizer NPK 17 : 8 : 9 (1.200 kg. ha-1) on the development of phytoplankton was carried out in two variations of an experimental fish farm of equal surface area of 0,1 ha-1 and depth 120 cm, during the culturing season from June to September, 1983. In the fish ponds carp fry were cultured from the larval stage to 3 months old along with stocked larvae at 250.000 ind. ha-1. The production of carp fry reached about 1.000 kg ha-1 in both variations, without supplement feeding the fish. In both variations of experimental fish ponds a similar phytoplankton community developed (QS=69%), which was composed of 151 species belonging to the systematic division of Cyanophyta (17), Euglenophyta (23), Pyrophyta (1), Chrysophyta (47) and Chlorophyta (61). The cenotic structure of phytoplankton in fish ponds treated with the fowl fertilizer made up 131 species, and in the fish ponds treated with the mineral fertilizer 105 species. In the amount of total phytoplankton between the two treated fish ponds certain differences were determined. The mean amount of phytoplankton in conditions of fertilizing with fowl fertilizer was 0,9x10-6 ind. l-1 (with seasonal dynamics from 0,04x106 ind. l-1 to 3x106 ind. l-1), and in conditions with mineral fertilization 3x106 ind. l-1 (with seasonal dynamics from 0,04x106 ind. l-1 to 5x106 ind. l-1). The dominant groups of phytoplankton were Cyanophyta and Chlorophyta, in that the dynamics of Cyanophyta during the culturing season in certain variations differed (Figures 1-5). The higher number values of the total phytoplankton, especially those belonging to the systematic division of Cyanophyta, show a greater trophic effect of the mineral fertilizer NPK (17 : 8 : 9) in comparison with the fowl fertilizer, however differential analysis did not determine a significance (p < 0,05).
