Study On The Relationships Among Tilapia, Periphyton And Submerged Macrophyte Vallisneria Spiralis

Fish can affect the water ecosystem by grazing and nutrient excretion, and omnivorous fish may feed in different habitats and thus can change coupling between habitats. Tilapia (Oreochromis niloticus) is the dominant species in freshwaters of South China, and its food includes phytoplankton in open water habitats and periphyton in substrate-surface habitats. In order to reveal the effects of tilapia on the interations among phytoplankton, periphyton amd submerged macrophytes, outdoor experiments were carried out by seting treaments with fish and controls without fish.The experiments analyzed the biomass (Chl a) of both phytoplankton and periphyton under, and the results showed that tilapia significantly reduced the biomass of periphyton. The mean values of Chl a of periphyton in tilapia group was 0.15 mg·cm-2 which was significantly lower than that of control group with a value of 1.26 mg·cm-2. And the mean values of phytoplankton Chl a in tilapia group was 31.99μg·L-1, significantly higher than that of control group having a value of 14.99μg·L-1. The relative growth rate of Vallisneria spiralis in tilapia group was-10 mg·g-1·d-1 which was significantly lower than that in the control group 7 mg·g-1·d-1. And tilapia significantly increased TN, TP and phytoplankton (Chl a) in the water, reduced the biomass of periphyton.The experiments suggest that:(1) Omnivorous tilapia can promote periphyton dominance shifting to phytoplankton dominance. (2) Grazing on periphyton and Vallisneria spiralis by tilapia likely contributes to the reduced biomass of periphyton and Vallisneria spiralis.Tilapia can affect the aquatic ecosystem via grazing and excretion, including eliminating inhibiting effect of periphyton on Vallisneria spiralis; reducing biomass of periphyton and biomass of Vallisneria spiralis; increasing the nutrient concentrations and promoting biomass of phytoplankton and so on. The study is on the relationship among tilapia; Vallisneria spiralis and periphyton to find the response of artificial water-system to tilapia, and provide suggestions to the natural water-systems'management.