The Experimental Study On The Effects Of Tilapia And Mud Carp On Water Quantity

Two outdoor micro-ecological experiments were designed to test the effects oftilapia and mud carp (Cirrhinus molitorella) on water quality.In the first experiment, the result demonstrated that the excretion rate of TP by tilapiawas higher than that by mud carp, but the excretion rate of TN by tilapia was lower thanthat by mud carp. The excretion rates of TN and TP by tilapia were 0.045 mg·g^-1WW·h^-1 and 0.0042 mg·g^-1 WW·h^-1. The excretion rate of TN and TP by mud carp were0.060 mg·g^-1 WW·h^-1 and 0.0034 mg·g^-1 WW·h^-1. The excretion of tilapia and mud carpboth enhance the phosphorus nutrient level including TP, TDP and PO₄-P and chlorophylllevel, however, the nitrogen nutriment level including TN, NO₃-N, NO₂-N and NH₄-Nwere lower when compared to the control treatments in the micro-ecological system.In the second experiment, the result demonstrated that there were a certain extentdifferences in the nitrogen and phosphorus nutrient level, chlorophyll and DO ofmicro-ecological system among tilapia, mud carp and control treatments. Fish presenceincreased the concentration of nitrogen and phosphorus, chlorophyll, but depleted the DO.The changes were more prominent for tilapia in nitrogen nutrient level, including TN,NO₃-N, NO₂-N, NH₄-N but less prominent in phosphorus nutriment level including TP,TDP, PO₄-P and PP than that for mud carp. Two main factors may be attributed to theobserved results: nutrient excretion and deliverance and nutrient utilization. It showedthat chlorophyll a concentration was correlated to dissolved inorganic nitrogen (r=0.53)and total phosphorus (r=0.54) concentration in mud carp groups, but it showed negativecorrelation in tilapia groups (r=-0.81, r=-0.82) and significantly correlation in controlgroups (r=0.78, r=0.97). We concluded that both species of fish can change the waterquality, significantly.