Studies On The Zooplankton Community Of Cultivating Duck And Fish In The Rice-Field

Rice field is the most important artificial wetland on the earth and the most disturbing ecosystem with abundant aquatic populations also. Present study had investigated the community composition and structure of zooplankton in the rice fields cultivating ducks and fishes at the Experimental Base of Huazhong Agricultural University from June to September 2008. During the experiment period, we examined the community composition and structure of Zooplankton including species composition, density, biomass, similarity, biodiversity. Simultaneously, the influences of ducks and fish on Zooplankton community in the rice fields were conducted in the present study.A total of 46 genus and 103 species were observed in this experiment, which consisted of 18 genus and 48 species for rotifer (46.6%),11 genus and 25 species for cladocera (24.3%),11 genus and 20 species for protozoa (19.4%),6 genus and 10 species for copepod (9.7%). Group D showed the most abundant (67 taxa) for species composition. Group R and DF was the minor (63 taxa for both groups) and Group F was the least (59 taxa). As a result, species richness of groups with ducks was superior to those of groups without duck and groups without fish exceeded that of groups with fish.Group R showed the maximal density of zooplankton (22.09×103 ind/L), followed by Group DF (12.48×103 ind/L) and Group F (12.65×103 ind/L), but Group D was the minimum (11.72×103 ind/L). Very little difference was found between the zooplankton density of Group D, DF and F. However, the density of zooplankton was significantly higher in Group R than in other groups (p<0.05). Based on these facts, fish and ducks decreased the density of protozoa. Ducks increased the density of large-sized zooplankton, but fish as the contrary.The maximal biomass of zooplankton was observed in Group R (33.10 mg/L), followed by Group D (25.33 mg/L), but Group F showed the minimum value (13.13 mg/L). The biomass of protozoa, rotifer and nauplius was higher in groups with fish and ducks than in control group. However, the biomass of copepodid, adult copepod and cladocera was the contrary, particularly in Group DF.The similarity index between Group R and the other three groups was higher than those among the other three groups. Cladocera showed higher similarity index than rotifer. As a whole, the similarity index of the same group tended to decrease during different period. For rotifer, similarity index between Group F and the other three groups was higher than those among the other three groups. For cladocera, similarity index between Group DF and the other three groups was lower than those among the other three groups.The Margalef index of rotifer was higher in groups with ducks than in groups without ducks. According to the density values, the Margalef index of zooplankton was higher in groups with ducks than in groups without ducks. The Margalef index of zooplankton was higher in groups with fish than in groups without fish based on the biomass values. Consequently, fish and ducks increased the Margalef diversity index of zooplankton in the rice fields.Rice field was absolutely artificial water body and showed unique characteristics concerning the community structure of zooplankton compared with natural water bodies such as lakes, reservoirs and cultivated lakes. Zooplankton was more appropriate to grow and breed in rice fields than in large-sized water bodies such as lakes and reservoirs.