Study On The Biology And Population Dynamics Of Schizothorax Waltoni

Schizothorax waltoni (Regan) belongs to the genus of Schizothorax, the subfamily of Schizothoracinae, the family of Cyprinidae and the order of Cypriniformes. S. waltoni, the unique species in China, only distributed in the upper and middle reaches of the Yarlung Tsangpo River and its tributaries. To study the biological characteristics of S. waltoni and its population ecology,1145individuals were collected from the Yarlung Tsangpo River and its tributaries (Xiang Qu and Nyang Qu) monthly from August2008to August2009. The main results are as follows:1. The typical pattern with translucent zones that alternated with opaque zones was found in otoliths, vertebrae and opercular bones of S. waltoni. The definition for annulus: otoliths> vertebrae> opercular bones. Annuli formed between March and May once a year in all of the three calcified structures. Between the vertebrae and otoliths, the I APE value was25.33%. Between the opercular bones and otoliths, the IAPE value was23.35%. For age classes1-20yeras, the average age is relatively close between vertebrae (10.57years) and otolith (10.64years), significantly higher than the opercular bones (9.65years)(p<0.05). For age classes>20years, the average age of the otolith (27.75years) significantly higher than that of vertebrae (18.50years) and opercular bone (19.50years)(p<0.05). In comparison, otolith is the best material for the age estimation of S. waltoni.2. The standard length (SL) of S. waltoni ranged from41mm to642mm, and weight (W) ranged from1.1g to3788.1g. The estimated age for females was4years to40years, male was4years to37years and undetermined was1years to9years. The fullness and coefficient of fat differed monthly in significantly (p<0.05). The correlations of otolith length/breadth/thickness/weight and fish length were higher than those of age.The SL-W relationship of S. waltoni were described as:W=1.365×10-5SL2984for females, W=1.238×10-5SL2.999for males, and W=3.664×10-5SL2.800for undetermined.The von Bertalanffy growth function for S. waltoni were described as:Lt=644.3{1-exp [-0.084(t-0.247)]} and Wt=3291.9{1-exp [-0.084(t-0.247)]}2.984for females, and Lt=586.2{1-exp [-0.084(t+2.250)]} and Wt=2477.9{1-exp [-0.084(t+2.250)]}2.999for males. The age inflexion point for the growth of female was13.3years, while it for male was10.8years.3. There is no shape difference between male and female except the spawning seasoa In spawing season, pearl organs cound be found in males but not in females. The ratio for female and male was1.19:1, which differed from1:1significantly (p<0.05). The gonad development of S. waltoni could be divided into6stages. S. waltoni were single spawners with a short-term spawning, they spawned once a year during March and April. The absolute fecundity of S. waltoni ranged from8338eggs to50021eggs, the relative fecundity ranged from5.1/g to22.4/g body weight. With the increase of standard length, body weight, and ovary weight, the absolute fecundity increased, but not correlation with ages. The standard length and age for the smallest sexual maturation female were243mm and6years, the first maturity of female were479.0mm and13.5years. The standard length and age for the smallest sexual maturation male were244mm and5years, the first maturity male were369.0mm and10.2years.4. The ingest intension of S. waltoni varied significantly over month and length classes (p<0.05). Macroinvertebrates was the main food for S. waltoni, especially the chironomid larvae and hydropsychidae larvae. The occurrence rate, the number percentage, weight percentage and relative importance percentage for macroinvertebrates were higher than other kinds of food. S. waltoni was a generalized food fish with high diet overlap within individuals. The feeding diversity (H’) and evenness (J) were different with season, fish size and sex. For S. waltoni, the selection index of macroinvertebrates and small invertebrates were higher, the shape of digestive organs could meet the needs of its feeding habits.5. For females, the total mortality was0.13/year, natural mortality was0.09/year, fishing mortality was0.05/year and exploitation level was0.35/year. For males, the total mortality was0.14/year, natural mortality was0.09/year, fishing mortality was0.05/year and exploitation level was0.35/year. The tr and tcfor females were3.43years and6years, those for males were2years and8years. The life history pattern of S. waltoni belonged to k-selection. At present, the resource of S. waltoni had been fished properly in the Yarlung Tsangpo River.