EFFECTS OF FEED INGMODELS ONWATER QUALITY FOR CHINESEM ITTEN CRAB ERIOCHEIR SINENSIS

Four factors, including the coverage of aquatic plants, the input of live snail, the ratio of animal based feed to to2tal feed, different feeding patterns, and three levels were followed to construct nine different feeding models by table L9(34) of the orthogonal design method1After feeding 540 two2year old Chinese mitten crabswith even weight and size in 27separate pens (6m ×5m ×215m) in the raising areas of east Taihu Lake for 240d, the effects of these feedingmodels with three replicates on the dynamic fluctuations of water quality parameters and plankton species were comparatively analyzed.The results showed that under the same density of released crabs, different feeding models exerted significantly different effects on the water quality and p lankton diversity index.Under the feeding model IV, the water quality was higherthan that of class Ⅲ water listed in the state environmental quality standards for surface water (GB383822002) , and evenhigher than that of nonraising areas outside the pens,which was evidenced by its chemical indices ofDO, CODCr , TP, TN,NH+42N,NO -22N and Chl a at 8145mg/L, 16146mg/L, 12150μg/L, 0146mg/L, 0110mg/L, 3160μg/L and 8112μg/L, respectively1The results from variance analysis indicated that the effects of the four factors on the water qualitywere listed inthe order of importance as: the coverage of aquatic p lants > feed casting patterns > the input of live snail > the ratio of ani2mal based feed to total feed1The results of“indicator organism”and Margalefps indices showed that the water biodiversityfrom model IV was significantly higher than that in nonculture areas, and its water body could be regarded as oligotro2phic1Based on the four factors,water quality parameters of CODCr , TP, TN, Chl a, and p lankton diversity index, a statisticalregression analysis was conducted1The results confirmed that the coverage of aquatic p lants and the feed casting patternshad close relations to these parameters.It is suggested that the feeding model,which is suitable for the culture of Chinesemitten crabs and beneficial to ecological protection of lakes, be characterized as follows: the coverage of aquatic plantsranged from 66% to 76% , the feed was given duringwhole growth and developmental stages and in the amount of 715% -510% of the crab weight, the amount of live snail input was 9000kg/ha, and the animal based feed accounted for 50% oftotal.