Studies On The Feeding Ecology Of Dominant Fishes And Food Web Structure Of Fishes In The Yibin Reach Of Yangtze River

The upper reach of Yangtze River is one of the areas with the most abundant freshwater fishery resources in China. In recent years, the fishery resources showed a trend of serious recession in the upper reach of Yangtze River. Artificial releasing is a common methods for restore freshwater fishery resources in the world, and many academics insist that some pre-study on the water area is necessary before releasing. The study includs that investigating the biological characteristics of releasing fish and ecosystem structure of releasing area, as well as the variation of ecosystem structure with seasonal. Both Ministry of agriculture and China Three Gorges Corporation have earring out many events of artificial releasing in fishes for recover fishery resources in the upper reach of Yangtze River. However, the data of biological characteristics of releasing fish and ecosystem structure of releasing area was lacking. The construction of hydropower engineering can affect community structure in fishes and the change of community structure, so the feeding ecology and community structure in fishes would change when the cascade hydropower stations started impoundment in downstream reach of Jinsha River.Based on the above research background, this article choose Yibin reach as a representative area in the upper reach of Yangtze River. Based the fish stomach sampled of dominant fishes and stable isotopes technology sampled of aquatic organism from 2012-2013 in Yibin reach, Academician Tang Qisheng proposed that the food web and its trophodynamics should be studied by using "simplified food web" and connecting the "points"and "facets". So the feeding ecology and the food web of fishes were studied at the levels of key fish species and dominant fish species and fish community, at the same time, the aquatic organism community structure and its seasonal variation were also studied in Xiangjiaba Dams impoundment before and after. The aims of the study in this paper are to provide basis data for better understanding of the transfer of nutritional matters and energy flow in Yibin reach, and offer theoretical basis for better understanding the effect of the Xiangjiaba Dams impoundment on aquatic ecosystem structure in Yibin reach, and instruct the theoretical direction for artificial releasing.1. An investigation of fish resources was conducted in Yibin reach, and the investigation was last time before Xiangjiaba Dams impoundment. A total of 62 fish species were obtained, in which 19 species were endemic in the upper reach of Yangtze River. And the 9 fish species were dominant species in catches, the name of fish was Coreius guichenoti, Pseudobagrus vachelli, Carassius auratus, Leptobotia elongate, Sinibotia supercilliaris, Silurus meridionalis, Coreius heterodon, Hypophthalmichthys molitrix, and Silurus asotus, respectively. The length-weight relationship was analyzed on dominant species, and the Catch Per Unit Effort (CPUE) was analyzed on main fishing net. The result showed that most of the fish was demersal and omnivorous, and they like to live in slow water environment. Compared with the history data, the result indicates that the demersal and omnivorous fishes were increasing, while fishes living in the torrent water and fishes spawning drift eggs were decreasing. CPUE and specifications of dominant fishes was significantly decreasing. In conclusion, the fish resources present recessionary trend in Yibin reach.2. For the key fish species, the diet composition and feeding intensity of Leptobotia elongata with ontogenetic and diel variations in Yibin reach were analyzed by stomach content analysis and stable isotopes technique. The result showed that Leptobotia elongata mainly feed on fish,crustaceans(shrimps and gammaridae),benthic invertebrates and aquatic insects larvae by stomach content analysis. And there was an significant change in the diet composition by stomach content analysis, that is, the Leptobotia elongata mainly feed on benthic invertebrates, when the body length is about 110mm,aquatic insects larvae when the body length<110mm, and shrimps and fish when the body length>110mm. The diet composition also had a change at about 210mm, and the shrimps was the most important prey items when the body length of Leptobotia elongata>210mm. In the stable isotopes technique, the POM, shrimps and fish are the main prey groups to Leptobotia elongata, and the results was consistent with the results of the stomach content analysis on feeding varation with different body length. The isotope values of potential food groups were different when when the body length>110mm, and the ratio of contribution of potential food groups was also different. the ratio of the contribution of POM was lower on Leptobotia elongata, in contrast, the fishes and shrimps were higher. The ratio of the contribution of shrimps was the highest when the body length of Leptobotia elongata>210mm. The feeding intensity showed that the main peaks of significant diel variations in spring of 2012, occurred at 09:30h and 12:30h, secondly at 18:30h, and the feeding intensity in day was higher than the night. In conclusion, the Leptobotia elongata was omnivorous fish, but it prefers carnivorous prey, and its diet has higher trophic plasticity. And the diet of Leptobotia elongata would be changed when the body length and temporal were different, so the Leptobotia elongata could be able to adapt the changes of hydrological environment and prey abundance in Yibin reach.3. For the dominant fish species, the diet of two coreius fishes (Coreius heterodon and Coreius guichenoti) and the feeding relationship between two coreius fishes in Yibin reach were studied by carbon and nitrogen stable isotopes analysis and also employing statistic methods such as cluster analysis. And the differences of the feeding apparatus morphological were also analyzed by the principal component analysis (PCA) between two species. The results showed that Coreius heterodon may be mainly feed on shrimps and POM, and Coreius guichenoti may be mainly feed on POM and Organic detritus. Dominant potential prey items were different between two coreius fishes, so the diet of two coreius fishes maybe have some differences. The prey similarity index is 78.69%, and the overlap coefficient is 55.59%. The PCA indicated that the morphological characters of the feeding apparatus were different when the body length was similar. In conclusion, the diet relationship of Coreius heterodon and Coreius guichenoti was not intense in Yibin reach, and two coreius fishes form their own Characteristics of feeding organs by long time evolution, the result of evolution was better to avoid intense for food resources. Therefore, we infer that the competition of diet relationship of interspecific was not intense in Yibin reach.4. The isotopes values of POM and aquatic organism were studied from different seasons in Yibin reach, and the variation of isotopes ratio was studied between the POM and the aquatic organism in different seasons. The results indicated that the effect on POM was significant from natural runoff of Yangtze River, the change was significant from the ratio of stable isotope in dfferent season, the ratio was the highest in flood period, lower in dry season, and the lowest in winter. The source of particulate organic matter was studied, and the results indicated that the source of POM were different in different seasons. The autochthonous organic matter and the allochthonous organic matter were the major source of POM in dry season, and the allochthonous organic matter was the major source of POM in flood period. C3 plant was was the major source of POM in all seasons except summer, C4 plant and organic pollutants produced by humans may be the major source of POM in summer. In fish, allochthonous organic matter was abundant and can be easily obtained in flood period. POM and Macrobrachium nipponensis were the important diet source of main fish in Yibin reach. The three food web models (River Continuum Concept:RCC; Flood Pluse Concept:FPC; Riverine Productivity Models:RPM) were discussed, respectively. The results indicated that just one of the three models was not suitable to the food web in the Yibin reach, two models (RCC and FPC) have to be referenced in flood period and three models(RCC, FPC and RPM) in dry season. The ?13C and ?15N of POM in spring of 2013 were fewer than those in spring of 2012, which indicated that Xiangjiaba Dams impoundment influenced the proportion from terrestrial exogenous organic matter and aquatic endogenous organic matter on particulate organic matter (POM), and the impoundment also affected the source of food and diet composition on aquatic organism. The contribution of organic matter from upperstream decreased in dry season, and the terrestrial exogenous organic matter from both sides and aquatic endogenous organic matter were the major composition of POM.5. For the aquatic organism communities, the seasonal variation in the trophic structure of familiar fish and shrimps communities in Yibin reach were examined by stable isotopes technique, and the effect of Xiangjiaba Dams impoundment was discussed on the structure of fish communities. The results showed that the fishes and shrimps usually dived into 4 groups:the first group is herbivorous group, and the species included Hypophthalmichthys molitrix; the second group is the omnivorous group of partial plants, and it including Macrobrachium nipponensis, Carassius auratus, Coreius guichenoti, Coreius heterodon, Pseudobagrus vachelli and Saurogobio dabryi; the third group is the omnivorous group of partial animal, included Rhinogobio ventralis, Rhinogobio typus, Silurus meridionalis, Sinibotia superciliaris, Gobiobotia filifer, Ctenogobius giurinus, Lepturichthys fimbriata and Leptobotia taeniops; the fourth group is carnivore group, included Leptobotia elongate(big individual), Siniperca scherzeri, Siniperca chuatsi and Siniperca kenrii. The trophic level of Limnoperna lacustris as section 2 in this paper, the trophic level from 2.5 to 4.75, and the number of trophic level was different in the different food chain. There are 2-3 levels among food chain of different seasons, and most of the fishes belong to secondary consumer with the trophic level from 3 to 4. On the one hand, the results indicated that the piscivores fish in higher trophic level was decline; on the other hand, the results indicated that the monophagous fish was difficult to exist, and the main fish species were omnivory in Yibin reach. In conclusion, the food web structure of fish was not stable in Yibin reach, and ecological system of river was not healthy. Local piscivores fish and herbivority fish were lacking, so the piscivores fish and herbivority fish were major release fish to keep richness of fish community in the upper reach of Yangtze river. The ?13C and ?15N values of 10 fish species were compared between before Xiangjiaba Dams impoundment and after, and the results showed that the ?13C values and ?15N values of majority fishes in the dry period before Xiangjiaba Dams impoundment were larger than in the dry period after Xiangjiaba Dams impoundment, and the results also indicated that the diet of most fish was influenced by Xiangjiaba Dams impoundment in Yibin reach, and the degree of influence was different with different fish species, which was greater on partial plant omnivorous fish and piscivores fish. The contribution of endogenous substances on the food wab of Yibin reach in the dry period before Xiangjiaba Dams impoundment was higher than that the dry period after Xiangjiaba Dams impoundment, and the contribution of organic matter was increased in Yibin reach after Xiangjiaba Dams impoundment.6. To table some proposal about artificial releasing in the upper Reach of Yangtze River, the body length of Leptobotia elongata shoud be greater than 110mm when release the fish into the river, and the releasing time choose April to June or October to November,which shuld avoid flood period and winter. As to releasing species, the local piscivores fish and herbivority fish should be released fish to keep richness of fish community in the upper Reach of Yangtze River. As to body length of releasing fish, the diet of size-shift of all species should be studied, thereby further to determine the body length of releasing in the upper Reach of Yangtze River. As to releasing time, the release of herbivority fish should be in flood period in in the upper Reach of Yangtze River; the release of the local piscivores fish should be avoid flood period when the body length of fish was small, and the local piscivores fish should be in flood period when the body length of fish was big enough.