Study on feeding preference of Spinibarbus hollandi to Spirogyra, Hydrilla verticillata and Ceratophyllum demersum and effect on water quality

The research on the feeding preference of Spinibarbus hollandi with gradient density (0, 26, 52, 104 g/m3) to Spirogyra, Hydrilla verticillata and Ceratophyllum demersum and effect on water quality were carried out to study the feasibility and safety of the biomanipulation of controlling Spirogyra by S. hollandi. Moreover, the grazing preference of the fish to Spirogyra and H. verticillata in different growth stages were also carried out and the intestinal contents have been microscopically observed. The result showed that S. hollandi significantly reduced the biomass of Spirogyra in the low density (26 g/m3) and feeding preference was:Spirogyra H. verticillata C. demersum. The fish prefer eating mature Spirogyra which has more harmful to environment and were harmless for young leaves of H. verticillata (stems6). The digestion mechanism is related to mechanical crushing with pharyngeal tooth. The nutrient of treatments were raised and then decreased due to the fish-grass symbiotic system, NH3-N, NO3--N and PO4--P of the low density (26 g/m3) were lower than the initial concentration after 21d, But the chl-a of all treatments were much higher than the control (0 g/m3) after 21d. It expected that the appropriate low density is more useful in the application, which could effectively control Spirogyra and be harmless to water quality, but the single application of the fish could not be suitable in the aquatorium where micro phytoplankton boom frequently happen.