PRIMARY PRODUCTION IN FISHPONDS AND ITS APPLICATION TO FERTILIZATION EXPERIMENTS

Abstract

Primary production was determined in fertilized and unfertilized fishponds in Israel by the “light and dark bottle” oxygen method. In the unfertilized ponds it was in summer 138–190 mg C/m 2 /hr; in the fertilized ponds it was 4 to 5 times higher. There was a sharp decrease of production with depth and in most cases the compensation layer in the fertilized ponds was at the depth of only 40 cm. Chlorophyll a concentration was high reaching a maximum value of 212.3 mg/m 3 in the fertilized ponds. Production per unit of chlorophyll and its variations with season and fertilization rate is discussed. Fertilization of fishponds with excessive amounts of fertilizers increases production in the upper layers of the water where favorable light conditions exist, but decreases production in the lower layers, where overshading by the plankton causes decreased light penetration. The effect of excessive doses of fertilizers may thus cause a lowering of production per unit area.