| The monitoring technology of environment DNA(e DNA)is a technology that directly extract DNA from environmental samples(water bodies,soil,air,etc.)to monitor organisms without contacting any target organisms,it has been widely used in the detection of various aquatic animals and species diversity analysis.First,the study optimized the e DNA method in the application of fish diversity analysis,and selected the suitable method for the Nansha wetland waters in the Pearl River Estuary.The fish community structure of Nansha Wetland was investigated comprehensively by e DNA method and bottom trawling,and the advantages and disadvantages of the two methods were evaluated in the application of fish resources survey.Therefore,the water samples of the Nansha Wetland Waters of the Pearl River Estuary were collected in September 2017(rainy season)and January 2018(dry season),respectively.And the structure of community diversity in fish were revealed comprehensively base on the e DNA method and bottom trawling,the results were as follows:1.The optimization of e DNA method fully considers the filtration volume(500 m L,1000 m L,2000 m L),filtration method(Fresh water samples and alcohol precipitation water samples)and different DNA extraction methods(Neasy Power Water kit(PW),DNeasy Blood and Tissue kit(BT)and Phenol-Chloroform method(FL))how to impact the DNA yield and quality.The result showed that the BT method capture the optimal DNA yield when it filtered1000 m L fresh water samples.and it was used in subsequent studies.2.In the study,a total of 78 fish species were detected base on the e DNA method and bottom trawling,belonging to 11 orders,31 families and 47 genera.There were 57 species were detected by the e DNA method,while 32 species were detected by the bottom trawling,indicating that the detection rate of e DNA was better.The historical datas showed that the Collichthys lucidus,Coilia grayii,Coilia mystus and Trichiurus japonicus were major economic fishes and dominant species in the Nansha Wetland in the Pearl River Estuary.In the present study,the high abundant species were Takifugu ocellatus,Glossogobius giuris,Takifugu alboplumbeus and Oxyeleotris marmorata,which belong to non-economic fishes,small fish or invasive alien species.The fishes of benthic carnivorous were still the important populations in the Nansha Wetland,which consistent with the structure of fish community of most wetland ecosystems.3.The present study showed that the spatial and temporal distribution of fish communities in the Nansha Wetland significantly different,which performing the fish diversity of dry season was more than rainy season and the number of species rised as survey sites increased.In addition,the fish species captured by bottom trawling method in the dry season(30 species)was significantly higher than that in the rainy season(14 species),while the different detected by e DNA method was not so significantly(47 species in the dry season,43 species in the rainy season).The results demonstrated the e DNA method performed higher stability compare to the bottom trawlling.The β diversity analysis based on the Whittaker index revealed that the distribution of fishes detected by the two methods have significant differences.The mean values of Whittaker index showed that rainy season was higher than dry season,indicating that the fish species of rainy season had greater difference in Nansha wetland.4.There are different habitats and activities between different fishes because of their different ecological habits.As far as perched aquifers were concerned,the fishes captured by e DNA and bottom trawling were both displayed benthic fishes > pelagic fishes > lower middle fishes for perched aquifers.Besides,the proportion of pelagic fishes and lower middle fishes was greatly different in the detection of bottom trawl method,one possible reason was that some fishes have a powerful ability to avoid some trawl catch,the other was the limitation of the trawl range.However,the number of species captured by e DNA method were more similar,indicating the less influence of fish activities for e DNA method.Besides,Hyporhamphus intermedius,Thryssa setirostris and Hypophthalmichthys molitrix were Filter-feeding species and the former two only were detected by e DNA method,indicating that e DNA method had higher detection rates for small,fast-swimming fishes.Furthermore,the benthic carnivorous fishes with weak swimming had a higher detection rate in the bottom trawl method,reflected that the bottom trawl method was greatly affected by fish activities.Overall,the BT extraction method used to filter fresh water samples about 1000 m L can performed better DNA production and yield,and it was used to analyze the fish diversity of Nansha wetland in the Pearl River Estuary.Compared to the bottom trawling method,e DNA method displayed better stability and accuracy for fish diversity survey in the water of Nansha wetland,and the fish species detected by the e DNA were greater than bottom trawling.The bottom trawl method is not only affected by the range of the trawl,but also deeply affected by the fish’s ability to move and the habitat of the fish(bottom landform).In addition,the bottom trawling with high randomness and low detection rate were mainly affected by the range of trawl,the activity and habitat of fish(bottom landforms).Furthermore,the fish distribution of Nansha Wetland has obvious spatial and temporal distribution characteristics,and the fish composition between dry season and rainy season was significantly different. |
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