Study On The Feeding Ecology Of Upper Fishes In Qili Lake,Anqing

Floodplain lakes are one of the most abundant and productive ecosystems in the world.They provide humans with rich ecosystem functions and services,and are the foundation of human sustainable development.There are many lakes in the middle and lower reaches of the Yangtze River,and most of the shallow lakes maintain hydrological connections with the main stream of the Yangtze River through rivers leading to the river,forming a river-lake complex ecosystem with extremely high biological productivity.In recent years,in order to meet the needs of human development,the construction of sluices and dams,the reclamation of lakes,water pollution,overfishing and other human activities have caused serious disturbances,causing problems such as rivers and lakes to block,habitat fragmentation,and aquatic environment damage.Lake ecosystem functions and fisheries resources have dropped significantly.Fish are an important part of the aquatic ecosystem and play an important role in indicating the structure and functional stability of the ecosystem.Their impact on the aquatic ecosystem is achieved through fish feeding,which affects its community structure and environment Material circulation and energy flow.Therefore,the study of fish feeding ecology will help to effectively utilize fishery resources and scientific fishery management.It also helps to deepen the structure of the aquatic ecosystem food web and the law of change,and ultimately provide a scientific basis for the management of aquatic ecosystems.This study selects Qili Lake in Anqing as the research site.Five sampling areas are set up,namely,lake inlet,tributary,littoral zone,lake center and lake outlet.In August2019（Wet season）,October 2019（Normal seasonⅠ）,January 2020(（Dry season）,and May 2020（Normal seasonⅡ）,the Qili Lake was investigated.The fish resources of the three lakes were investigated,and samples of gastric and intestinal contents and muscle samples of 5 species of pelagic fish such as Hemiculter bleekeri,Acheilognathus taenianalis,Coilia brachygnathus,Toxabramis swinhonis Gunther,and Culter alburnus Basilewsky were collected in lake center,tributary and littoral zone.Analyze the status of fish resources in Qili Lake from the aspects of species composition,ecological type,and diversity level,compare the changes in fish community structure at different water levels,and analyze the main influencing factors that cause the changes in fish community structure;based on the gastrointestinal content analysis method and stable isotope analysis method to study the food composition,feeding intensity,food selectivity and food competition of 5 pelagic fishes.It is expected to provide basic information for the construction of the Qili Lake food web and provide scientific basis for the protection of fish resources in the lakes along the lower reaches of the Yangtze River.The main findings are as follows:1.Current status of fish resources in Qili Lake,Anqing:A total of 47 species of fish were identified during the survey,belonging to 4 orders,10 families and 36 genera.Carps accounted for 65.96%,and more than 60%were freshwater settled fishes,mainly inhabiting China.The upper waters are dominated by plankton-eating fishes,among which Pseudobrama simoni is the first dominant species.The results of one-way analysis of variance showed that the average number of fish species in the wet and flat periods were 35 and 33 respectively,which were significantly more（P<0.05）than 22species in the dry period;the average catch in the wet period was 1,008,Significantly（P<0.05）higher than the 662 tails and 594 tails in the normal and dry seasons,and The average catch weight in wet season was 24.09 kg,which was significantly（P<0.05）higher than that in normal season and dry season.The average catch weight was 19.56kg and 19.99 kg,respectively,but there was no significant difference between normal season and dry season（P>0.05）.The results of diversity analysis showed that the fish diversity and richness index in the wet season were significantly higher（P<0.05）than in the dry season,but the dominance index was only 0.14,which was significantly（P<0.05）lower than in the dry season.The results of cluster analysis showed that there was a significant difference in the fish community between the low water season and the high water season（R=0.531,P<0.01）.In general,abundance The diversity of fish communities in the water period is higher than in normal and dry periods.Water level,temperature,total phosphorus,transparency and zooplankton biomass are important environmental factors affecting fish community structure（P<0.05）.2.Food composition of pelagic fish:The analysis of gastrointestinal contents showed that the five pelagic fish ingested a total of 11 types of food organisms,and the most abundant species of Hemiculter bleekeri and Acheilognathus taenianalis,both of which were 11 types,the second species were Cultrichthys erythropterus and Coilia brachygnathus,both of which had 8 species,with the least Toxabramis swinhonis and only 6 types.Cyanophyta and cladocera were the dominant feed organisms in the diets of Hemiculter bleekeri（IRI%=37.48%and 54.71%）,Cultrichthys erythropterus（IRI%=40.86%and 38.18%）and Toxabramis swinhonis（IRI%=45.95%and 47.60%）.Cyanophyta,cladocera and copepods（IRI%=41.49%,35.46%and 21.47%）were the dominant species of Coilia brachygnathus,while Bacillariophyta and cladocera were the dominant species of Acheilognathus taenianalis（IRI%=37.76%and 32.36%）.Except for Toxabramis swinhonis,the food groups of the four fishes were different in different water periods.In dry season（10 types）,Hemiculter bleekeri has the largest number of food groups,and normal season I（7 types）is the least,Bacillariophyta and cladocera are the dominant food in normal season I and dry season,and cyanophyta are the main food in wet season;The food group of Coilia brachygnathus in normal season I（8 types）is more than that in normal season II by 2 types,the food in normal season I is mainly Copepods,and in normal season II it is mainly Cyanophyta;Cultrichthys erythropterus have the most food groups in normal season II（8 types）,and the least in normal season I（3 types）,normal season II and wet season,Cyanophyta and Cladocera are more dominant,Bacillariophyta are the highest in in normal season I,and Chlorophyta and Copepods are more dominant in dry season;The feeding group of Acheilognathus taenianalis was the most in normal season II（10 species）,and the least in dry season（7 species）,Cryptophyta was the dominant feed group in normal season II,Cyanophyta and Cladocera were in wet season,and Bacillariophyta,Cladocera and Copepods were in wet season and dry season.The results of stable isotope analysis showed that theδ¹³C value of each food source varied from-26.56‰to 31.85‰,and theδ¹⁵N value varied from 4.40‰to 12.40‰.One-way analysis of variance showed that there were significant differences in theδ¹³C andδ¹⁵N values of zooplankton,aquatic plants,and particulate organic matter（POM）in different water period（P<0.05）;Phytoplankton and juvenile fish have no significant difference in theδ¹³C value between water periods（P>0.05）,and there is a significant difference inδ¹⁵N value（P<0.05）;for shrimp,theδ¹³C value changes significantly（P<0.05）,and there is no significant difference inδ¹⁵N value between water periods.（P>0.05）.According to the calculation of the Isosource model,plankton contributes the most to the food sources of the three fishes:Acheilognathus taenianalis（40.20%）,Hemiculter bleekeri（43.10%）and Toxabramis swinhonis（44.10%）,while shrimps and juveniles contribute the most to Cultrichthys erythropterus（32.50%）and Coilia brachygnathus（42%）.Different food sources have different contributions to pelagic fish in different water period.Phytoplankton is an important food source for Hemiculter bleekeri in wet season,and there are a wide range of food sources in normal season I and dry season,phytoplankton,zooplankton and POM are all important food sources,while the food sources of Cultrichthys erythropterus are extensive in normal season II,the six types of phytoplankton,zooplankton and POM are all important food sources,the other three water period eat mainly POM and juvenile fish;Coilia brachygnathus feeds on shrimps and juveniles in normal season I and normal season II,and juveniles in dry season;In normal season II,wet season,and dry season,the food sources of Acheilognathus taenianalis are mainly phytoplankton and zooplankton,in normal season II,it is mainly composed of attached organisms,aquatic plants and POM.3.Feeding intensity:In general,the feeding intensity of Acheilognathus taenianalis and Hemiculter bleekeri is higher than that of Toxabramis swinhonis,Cultrichthys erythropterus and Coilia brachygnathus.Except for Toxabramis swinhonis,there were significant changes in the feeding intensity of others in different water period（P<0.05）.The feeding intensity of Hemiculter bleekeri is the highest in dry season and the smallest in normal season I;the feeding intensity of Coilia brachygnathus is higher in normal season I than that in normal season II;the feeding intensity of Cultrichthys erythropterus is the largest in normal season I and the smallest in dry season;the feeding intensity of Acheilognathus taenianalis in wet season is significantly higher than that in dry season.4.Food selectivity and food competition:In terms of food selectivity,the five pelagic fishes show a strong tendency to actively select Cladocera and Copepods,and at the same time they show active choices for some small individual plankton,and the food selectivity changes obviously.For example,Hemiculter bleekeri actively selects protozoa in wet season,but strongly avoids it in dry season;Cultrichthys erythropterus strongly avoids Bacillariophyta in normal season II and wet season,and has a tendency to actively eat in normal season I.In terms of food competition,there may be serious food overlaps between fish species with similar feeding habits in different water period.For example,the food overlap coefficient of Hemiculter bleekeri and Acheilognathus taenianalis is close to 0.70 in wet season and dry season,indicating intense competition,it is only 0.11 in normal season I,indicating food competition.The food overlap coefficient of Hemiculter bleekeri and Toxabramis swinhonis is 0.81,and the food competition is very fierce in wet season.However,the food overlap coefficient of Coilia brachygnathus and Cultrichthys erythropterus was the highest only in dry season,which was 0.76,indicating severe food overlap.