A Preliminary Study On The Ecology Aspects Culture Of The Crayfish (Procambarus Clarkii) In Rice Fields

Culture of the crayfish(Procambarus clarkia) in rice fields is an important mode in China. Currently, the area of rice fields used for culture of the crayfish is more than30thousand ha in Hubei Province, where the rice-crayfish farming has brought a large quantity of economic, social and ecological benefits. However, there is few information on the culture of the crayfish in a rice-based farming system. A preliminary study of phyiso-chemical characteristics of water, phytoplankton and the biology of the crayfish was conducted at the base of eco-culture of crayfish in rice fields in Qianjiang City during the period of from May to October in2013. The results of this study will be useful for further understanding the structure and function of the rice-crayfish farming systems and providing ecological bases for the enhancement of technology of crayfish culture in rice fields. The main results were as follows:1. There was a seasonal change in turbidity, dissolved oxygen, pH, conductivity, chemical oxygen demand, total nitrogen, ammonium and total phosphorus content in the water of crayfish-farming rice fields. In addition, those water parameters were also influenced by some farming activities such as rice planting, fertilizing and harvesting. Monthly average of turbidity ranged21～65NTU; dissolved oxygen1.02～5.18mg/L; pH7.2～8.4; conductivity432～594us/cm; chemical oxygen demand4.58～8.72mg/L; total nitrogen1.113～3.644mg/L; ammonium0.476～1.843mg/L; total phosphorus content0.031-3.645mg/L.2. Species composition, density and biomass of phytoplankton in the water of crayfish-farming rice fields were investigated. A total of86phytoplankton species was recorded, belonging to7Phylums and52generas. Of which there was13species in Cyanophyta;15species in Bacillariophyta;9species in Euglenophyta;43species in Chlorophytaand. The annual average density of phytoplankton was10.4×106cells/L, of which Chlorophyta and Cyanophyta accounted for51.5%and26.2%. respectively. The annual average biomass of phytoplankton was2.62mg/L, of which Cryptophyta, Bacillariophyta and Chlorophyta accounted for37.5%、23.2%and14.1%, respectively. The dominant species were Chlorellaceae vulgaris, Gloeocapsa sp., Crucigenia quadrata, Nitzschia palea, Melosira granulate, and the top three species are eutrophic indicator species and the last two species are mesotrophic indicator species.3. A total of700individual of the crayfish was collected and measured randomly. The regressive relationship between total length and weight, carapace length and weight, total length and carapace width, carapace length and width were obtained. The seasonal change in total length, body weight and condition factor of both male and female was analyzed. Sex ratio (males to females) in every month was investigated. The frequency of male individuals was significant bigger than females in May, but in other month (from June to September) the frequency of males was significant smaller than females.