| Poyang Lake, China's biggest freshwater lake, locates on the south riverside of the middle and lower reaches of Yangtze River (28°24'-29°46'N, 115°49'-116°46'E). The lake lies at the convergence of 5 rivers, such as Ganjiang River, Fuhe River, Xinhe River, Raohe River and Xiushui River, and helps regulate water in the Yangtze River by providing water through Hukou County. The fish resource in Poyang Lake is abundant. Culters is a popular and important economical carnivorous freshwater fish in China which feeds on small fish and shrimp. It is important to study and exploit the resource of Culter in Poyang Lake, however, little information is available about this field. Therefore, studies focused on the Culter population in Poyang Lake are meaningful.In the present study, we analyzed the differences of the body shape, brain shape, and growth characteristics among Culter alburnus, C. mongolicus, C. dabryi and Cultrichthys erythropterus, the diversities of body shape, gill arch and scale of C. mongolicus, and discussed the events about the morphometric separation of fish population in Poyang Lake. The results are shown as follows:1. A total of 633 samples of Culter were assigned into 16 groups according to 4 body length zone. 13 landmarks were used for geometric morphometric analysis of body shape through TPS Program and STATISTICA Program Version 6.0. The results showed the diversities of body shape among four species are more than among the growth phases. The changes of body shape depends on the slow growth of head length and caudal length in Culter alburnus, C. mongolicus, and C. dabryi, the distinct growth of the back of the body behind head as one of main characters in C. dabryi, the slow growth of body depth than standard length, but in the stage of standard length which between 150mm- 250mm, the obvious growth of the length and depth of the later trunk region in Cultrichthys erythropterus.2. The brain shape data were collected from 48 samples. 21 brain morphological characters were measured by using Motic Images Advanced Program Version 3.2, and 34 landmarks were used in geometric morphometrics analysis. There were the distinctions on shape of the cerebellum and length of the tractus olfactorius between genus Culter and genus Cultrichthys. The morphological differences of brain among Culter alburnus, C. mongolicus, and C. dabryi showed as the subtle differences in each brain section. 3. A total of 126 Culter mongolicus Basilewsky were collected from 7 different sampling points. 14 traditional eigenvalues and 24 truss-based eigenvalues were measured. 13 landmarks were used for geometric morphometfic analysis. The multivariate discriminant function analysis and cluster analysis showed that there were significant differences in the body shape among 7 groups. In the region of the Lake Poyang, 7 groups should be divided into two sample-groups in the present study. They were: (1) PYH 1 + XKH + NBG + GSH. (2) PYH 2 + PYH 3 + XMH. Furthermore, first sample-group could be divided into two inferior sample-groups, PYH 1 + XKH + NBG sub-sample-group and GSH sub-sample-group. GSH sub-sample-group was more close to the second sample-group. Within PYH 1 + XKH + NBG sub-sample-group, NBG closes more near to GSH sub-sample-group than PYH 1 + XKH. The depths, such as head depth, body depth and caudal depth, and head length, especially snout length, and the eyes' relative position were related to the different characters among the 7 geographical groups. They are scattered in the order of the geographical latitude but not of the artificial dams' position. The populations of C. mongolicus in the Poyang Lake could be related to the sites of connection with some rivers, for example, Fuhe River, Xinjiang River, Changjiang River, the south of Raohe River, the middle of Ganjiang River and Xiuhe River , and the north of Yangtze River. The specimens, from NBG, XMH and XKH, were used for gill arch and scale morphometric analysis. The regression equations for standard length and the measurements of gill arch, such as gill-arch length, number of gill-raker, gill-raker length, mean gill-raker width, and mean gill-raker spacing, and 6 shape factors and 5 shape indices of scale were calculated. ANOVA, principal components analysis and discriminant function analysis showed that there were significant differences in the gill arch and the scale among 3 groups, and more similar between NBG and XKH. We thought there are two or more populations of C. mongolicus in Lake Poyang.4. All specimens, 232 Culter alburnus, 169 C. mongolicus, 79 C. dabryi and 121 Culterichthys erythropterus were collected from Lake Poyang and the age divided into 0+-4,0+-5,0+-7,0+-6 age groups. The higher percentage of the samples' age ranges were 0+-l (65.9%) ,2+-3 (33.1%) ,1+-2 (29.1%) , 2+-3 (32.2%) . The results showed that the scale-radium takes on linear relationship with standard length, L=10.4399+100.1273×SR, L=52.8778+65.4337×SR, L=76.3400+43.1301×SR,L=40.0273+48.1733×5R. The regression equation for standard length and body weight is W=6.3×10-6L3.1054, W=8.08015×10-6L3.0893, W=2.5×10-6L3.3319, W=3.1×10-6L3.2975, and growths of them take on a constant speed style. The regression equations for body weight, side area and width are feasible. In the present study, the power equations the can give better results are W=4.05051×100-2×A0.66260×T1.41994, W=3.18603×10-3×0.66845×T1.44376, W=1.99310×10-3×A0.70982×T1.47305, and W=3.58823×10-3×A0.63253×T1.494655. Growths of four species of Culter can be described with von Bertalanffy equations, namely standard length growth equation, body weight growth equation, body weight growth inflexion point, and with the corresponding standard length and body weight:C. alburnus: Lt=872.04×[1-e-0.1667×(t+0.161)], Wt=8528.64×[1-e-0.1667×(t+0.161)]3.1054, inflexionpoint 6.96 age, Lt=606.08mm,Wt=2755.59g; C.mongolicus:Lt=568.8247×[1-e-0.1856×(t+0.1634)], Wt=2620.4407×[1-e-.1856×(t+0.1634)]3.0893,inflexion point 6.24 age, Lt=395.53mm, Wt=852.90g; C. dabryi: Lt=353.6449×[1-e-0.2218×(t+0.6582)], Wt=775.3749×[1-e-0.2218×(t+0.6582)]3.3319,inflexion point 6.08 age, Lt=274.30mm, Wt=332.54g; C.erythropterus::t=327.3487×[1-e(-0.2112×(t+1.0745)],Wt=608.9887×[1-e-0.2112×(t+1.0745)]3.2975,inflexion point 4.57 age, Lt=228.08mm, Wt=184.98g.6. A total of 517 specimens of genus Culter, 235 C. alburnus were collectd from different localities and were used for morphometric analysis. The results of discriminant analysis and cluster analysis indicated that four species-groups could be divided. C. dabryi shinkainensis was significantly different from C. dabryi dabryi in body forms, so C. dabryi shinkainensis should be changed to species, instead of subspecies, namely Culter shinkainensis (Yih et Chu), 1959. The 6 populations of C. alburnus (Basilewsky), from Lake Poyang, River Songhua, River Liaohe, River Jialing, River Lijiang and Lake Taihu, should be classified as different geographical populations, but not subspecies.
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