Trophic Structure Of Fish Communities In Weishui Reservoir Based On Stable Isotope Techniques

Large surface fishery is an important part of freshwater fisheries of China,and it plays a crucial role in building water ecological civilization,ensuring the supply of high-quality aquatic products,promoting industrial integration,and increasing income of fisheries.Until 2019,the area and output of large water surface aquaculture accounted for42.8%and 12.4%of total freshwater aquaculture,while the ecological aquaculture area in reservoirs accounted for more than 70%of the total large water surface aquaculture area.Compared to pond aquaculture,many lakes and reservoirs are underutilized for natural feed resources.At present,many studies on ocean and river food webs have been reported.However,little attention has been paid to those on lakes and reservoirs.Carbon sources are basal energy sources of the food webs.Research on the utilization of carbon sources help to understand the process of energy flows in reservoir.In order to investigate the fishery structure and utilization of food resources for fish,the characteristics of fish community structure in summer and autumn of 2020 were studied based on carbon(δ¹³C)and nitrogen(δ¹⁵N)stable isotopes techniques,and a bayesian mixing model was used to evaluate the contributions of four potential carbon sources（POM,terrestrial plants,periphyton algae,organic detritus）to the diet assimilation of different fishes.The results showed that there were seasonal differences in the trophic structure of fish communities in Weishui Reservoir.The trophic level length（NR）,basal food source（CR）,total ecological niche space TA),overall community density（NND）,trophic niche distribution range（SDNND）,and core ecological niche space（SEAc）of fish communities in summer were greater than that in autumn,with a high diversity of food sources and low degree of trophic redundancy.Fish communities in Weishui Reservoir primarily depended on exogenous carbon sources in summer and autumn,but there were obvious differences between the carbon source utilization in the two seasons（P<0.05）.Overall,terrestrial plants made the most contribution to the carbon sources of fish community in Weishui Reservoir.Trophic positions（TPs）of fish in summer ranged from 2.5-3.5,with an average of 3.01,while TPs of fish in autumn ranged from 2.9-3.8,with an average of 3.32.By analyzing the TPs of fish with different feeding habits,it was found that TPs of fish in autumn were generally higher than those in summer.This study revealed that the utilization of carbon sources by fish with different feeding habits exhibited significant differences in summer and autumn.TPs of fish in autumn were generally higher than those in summer.This is mainly because low water levels in autumn was not conducive to input of terrestrial plants,which resulting in intensified competition of fish for food resources and enhanced predation of aquatic food webs.Our results will provide useful basis for further research on the trophic structure of biological communities in the Weishui Reservoir and studies on the material cycle and energy flow of other reservoir ecosystems.