Study On Feeding And Excretion Of Three Little Fishes And Their Effect On Water Quality Of Qiankeng Reservoir In Shenzhen City

It is not only low-cost but also high social and all-around benefit to purify water by biological method. The feeding and excretion of three little fishes (Hemiculter. leucisculus, Tilapia. aurea and Cirrhinus. molitorelld) was studied and their effect on water quality of Qiankeng reservoir in Shenzhen City Around the topdown effect of fish was also studied. Based on the analysis of their stomach contents, their diet composition was assayed. The three fishes' feeding rhythm in cage and their rate of digestion indoor were looked into, and their daily ration was estimated through the method of daily average fullness index. Using the spectrophotometer, the content of chlorophyll a in the stomach (gut) was measured, and the feasibility of taking the chlorophyll a as an index of measuring the feeding of fish on phytoplankton was studied. Adopting the national standard method, the effect of the three fishes' excretion on total nitrogen, total phosphorus, CODMn, pH, turbidity and conductivity coefficient was surveyed. The effect of feeding and excretion offish on water quality was discussed and the results revealed as follows:H. leucisculus shows omnivorous and preference for cladocera and rotifera. T. aurea shows phytoplanktivorous and preference for euglenophyta and rotifera. C.molitorella shows mainly phytoplanktivorous. The number of H.leucisculus and T. aurea as well should be controlled in view of their diet composition.The daily rate of food consumption of H. leucisculus is about 2.4%; the rate of digestion (passage time) is about 44 h; the daily ration is about 1.1%. For C.molitorella, the daily rate of food consumption is about 2.5%; the rate of digestion is about 51 h; the daily ration is about 1.2%. For T.aurea, the daily rate of food consumption is about 3.2%; the rate of digestion is about 66 h; the daily ration is about 2.3%.The chlorophyll a in the gut is stable and can be regarded as an index of measurement for fish's feeding on phytoplankton.The effect of excretion on water quality items was analyzed, including total phosphorus, total nitrogen, chemical oxygen demand, pH, turbidity and conductivity coefficient. The excretion raises the conductor coefficient and turbidity and lower pH. On total nitrogen and CODMn, the effect of H.leucisculus and T.aurea is greater, and their number should be controlled. On total phosphorus, the effect of C.molitorella and T.aurea is greater, and their number should be controlled.