In situ growth and photosynthetic activity of Cyanobacteria and phytoplankton dynamics after passage through the gut of silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), and Nile tilapia (Oreochromis niloticus)

Abstract

The growth and photosynthetic activities of Cyanobacteria passed through the gut of silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), and tilapia (Oreochromis niloticus) were compared with those of phytoplankton taken directly from Lake Taihu during a 13-day in situ dialysis culture. After the first 3–5 days of reduced activity after excretion by silver carp and bighead carp, the photosynthetic activity of Cyanobacteria recovered and rose significantly higher (P < 0.01) than levels in the control population, whereas there was a notable reduction of photosynthetic activity after passage through tilapia gut. The phytoplankton biomass showed a 2- to 3-fold increase of growth, and extracellular polysaccharide production was also stimulated after passage through silver carp and bighead carp gut. Chlorophyta fluorescence was detected at much higher levels than that of Cyanobacteria and Bacillariophyta after passage through tilapia gut. Scenedesmus obliqnus and Chlamydomonas sp. contributed much to the growth of the Chlorophyta during the in situ cultivation. However, the total phytoplankton biomass showed a distinct reduction in the tilapia treatment during the culture. The study indicated that Nile tilapia feeding and defecation may help remove Cyanobacteria from the water column and favor a community shift to Chlorophyta.