WATER BLOOM OF BLUEGREEN ALGE IN CARP FISHPOUNDS

Abstract

The massive development of bluegreen algae (Cyanophyta/Cyanobacteria), the so--called water bloom, is a frequent phenomenon in fishpond ecosystems. This study analyses water bloom development in three carp fishponds owned by a fishbreeding company at Donji Miholjac (Croatia), where one-year-old carps (Cyprinus carpio) , were bred in defferent fishstock densities. Analyses of physicallychemical properties of water and phytoplankton biomass were per- formed in fortnight intervals from May till October, 1992. In all there investigated fishponds the water bloom of bluegreen algae developed, but at a different time and showing a different qualitative composition. In the fishpond with fishstock density of 250 kg/ha water bloom consisted of the species Aphanizomenon flos-aquae, and the biggest biomass (131.92 mg/I) was found in August. In the fishpond with fishstock density of 437 kg/ha a water bloom consisting of species from the genues Anabaena and species Aphanizomenon flos-aquae developed at the end of July. In the fishpond with the so--called intensive breeding (fishstock density of 750 kg/ha) water bloom of the species Microcystis aeruginosa developed as late as September. The beginning of water bloom development was caused by the low value (lower than 7) of the ratio between the quantities of total phosphorus and total nitrogen. However, the qualitative composition of water bloom was influenced by one-year-old carp fingerlings density.

Keywords

• bluegreen algae (cyanophyta/cyanobacteria)
• biomass
• water bloom
• carp fishpond