Study On The Biology And Population Dynamics Of Schizothorax O' Connori

Schizothorax o'connori belongs to genus Schizothorax, subfamily Schizothoracinae, family Cyprinidae, order Cypriniformes. Schizothorax o'connori is the unique species in China, which distribute in the upper and middle reaches of the Yarlung Tsangpo River and its tributaries. In total,1126 S. o'connori individuals were collected from the Yarlung Tsangpo River (98.9%) and its tributaries (Xiang Qu and Nyang Qu) monthly from August 2008 to August 2009. Biology and population ecology of S. o'connori were studied. The aquatic organisms in Xaitongmoin reach of the Yarlung Tsangpo River were also investigated. The main results are as follows:1. Otoliths, vertebrae and opercular bones of S. o'connori showed the typical pattern with translucent zones that alternated with opaque zones. Annuli formed between March and May once a year in all of the three calcified structures. Annuli on otoliths were clearer than others. The IAPE value of vertebra vs. otolith was 9.3%, while that of opercular bones vs. otolith was 11.4%. For age classes 1-21, The IAPE values of vertebra vs. otolith were almost below 11%, and mean values of age estimates from different structures showed no significantly difference (p>0.05) between otolith and vertebra. Otolith was the most accurate structure for age estimation of S. o'connori, followed by vertebra and opercular bone.2. The standard length (SL) of S. o'connori ranged 33-553 mm, weight (W) ranged 0.6-2982.6 g, the estimated age range varied from 1 to 50. The maximum age observed was 50 years for females and 40 years for males. Length-weight relationship was described as W=2.034×10-5 SL2.940. Fullness and Coefficient of fat differed monthly. The correlations of otolith dimensions (length, breadth, and weight) and fish length were higher than those of age. The von Bertalanffy growth function were:Lt=499.7 (1-e-0.095 (t+0.896)) and Wt=2666.2 (1-e-0.081(t+0.946))2.94 for females, and Lt=576.9 (1-e-0.081 (t+ 0.946)) and Wt=1748.1 (1-e-0.095(t+0.896))2.94 for males. The inflexion point for the growth of female and male were 12.4 and 10.5 years, respectively.3.74 genera,6 phyla of phytoplankton,46 genera,3 phyla of zooplankton,104 genera, 12 phyla of periphyton,28 genera or family,12 phyla of zoobenthos were observed in this investigation. The density and biomass of phytoplankton and zooplankton were highest in Autumn, while those of periphyton were highest and lowest in Spring and summer. And density and biomass of zoobenthos were highest in Autumn and Spring, respectively. Shannon-Wiener index (H) and Pielou's evenness index (J) of phytoplankton were highest in Spring, while those of periphyton and zoobenthos were highest in Summer. The most item in periphyton was diatoms, and the most item in zoobenthos was Chironomida larvae.4. The ingest intension varied significantly over month and length classes (p<0.05). S. o'connori fed on diatoms, green algae, cyanophytes, other algae, small invertebrates, and macroinvertebrates. Diatoms was the most important food, in term of number, weight and relative importance. Some differences were observed in Feeding diversity (H) and evenness (J) over season and fish size. The Amundsen figure indicated that S. o'connori was a generalized feeder with high diet overlap within individuals. Diet composition was relatively heterogenous among seasonal groups, while high degrees of diet overlap were found for prey composition among fish length and sexes.. S. o'connori grazes periphyton (mainly diatoms) attached to rocks, and the shape of digestive organ corresponding to its feeding habits.5. There are pearl organs on rostral side, orbit vicinity and fin rays of males in spawning season. The female and male ratio was 1.20:1, which differed significantly from 1:1. Standard length, weight and age of the females at first maturity were 433.0 mm, 1147.16 g and 16.2 years, respectively, and those of the males were 359.4 mm,663.36 g and 12.5 years, respectively. According to macroscopic stage of gonads, gonadosomatic index (GSI) and the size distribution of oocytes over month, S. o'connori were single spawners with a short-term spawning pattern during February and April. The fecundity ranged 8228-39343 (21190±6990) eggs, and the relative fecundity ranged 7.0-25.8 (16.8±3.9)/g body weight. The fecundity increased with standard length and body weight, but had no significant correlations with ages.6. The total mortality was 0.09/year for females and 0.11/year for males. Natural mortality was 0.05/year for females and 0.06/year for males, and fishing mortality was 0.04/year for females and 0.05/year for males. Exploitation level of S. o'connori was 0.44/year for females and 0.45/year for males. Took Huso dauncus and Eleotris oxycephaoa as reference, the life history pattern of S. o'connori belonged to k-selection. Assessing the stock status using the spawning stock biomass per recruit model, we concluded that the resource of S. o'connori had already been fished proporly in the Yarlung Tsangpo River.