Growth,Food Composition And Genetic Diversity Of Juvenile Chinese Sturgeon(Acipenser Sinensis)in The Yangtze Estuary

Chinese sturgeon,Acipenser sinensis Gray,is a typically anadromous fish.Historically,Chinese sturgeon were distributed in several major river systems and used coastal habitats throughout southwestern Korea;Kyushu,Japan;and the Yellow,Yangtze,Pearl,Min,and Qiantang Rivers in China.Currently,they are only found downstream of Gezhouba Dam in the Yangtze River where they spawn and in the Yellow and East China Seas where juveniles and adults forage.Extensive studies have shown that the natural resources of wild Chinese sturgeon decreased rapidly since the closure of Gezhouba Dam.Chinese sturgeon is on the verge of extinction and was listed as a Category?nationally protected species in China since 1988.And in 2010,this species is considered by the International Union for the Conservation of Nature?IUCN?as critically endangered.From 2013 to 2015,natural propagation of Chinese sturgeon was not observed in the spawning ground,it faces survival crisis.On April16^th,2015,a wild Chinese sturgeon was collected in the Yangtze Estuary,and more than thousands of juveniles were observed during May to September.The Yangtze River Fisheries Research Institute reported a resumption of spawning in 2016,and the East China Sea Fisheries Research Institute observed migrating juveniles in the Yangtze Estuary.1.Growth and food composition of juvenile Chinese sturgeon in the Yangtze estuaryThe present study was conducted to assess growth and the feeding ecology with prey preferences of juvenile Chinese sturgeon individuals in the Yangtze Estuary from May to August,2015.From May to August,juveniles grew from 11.65±2.10cm?10.82±6.32g?to 27.78±3.36cm?158.08±60.50g?,and the length-weight relationship?a=3.1124?indicated isometric growth.The SV of body weight in this study was higher than juveniles in 2004,the population show greater differences in growth.The stomach content analysis indicated the following order of dominance of prey groups:fish,crab,amphipoda,polychaeta,shrimp and other small benthic invertebrates.The main diet taxon has not changed dramatically compared with samples in 2004.Moreover,this study confirmed that changes occurred in the prey composition,which was different with the growth of length size in the Yangtze Estuary.Analysis of individual sample stomach contents revealed that about 50%of the stomach contents contained only one species of food organism,implying that the juvenile Chinese sturgeon had insufficient biological abundance in the Yangtze River estuary,and the growth difference exhibited by Chinese sturgeon was likely to be a result of diet.Therefore maintaining species richness in the Yangtze Estuary and ensuring sufficient food source is crucial to species conservation of Chinese sturgeon.2.Population genetic diversity of Chinese sturgeon based on the mitochondrial control region?D-loop?sequenceA 462 base pair mitochondrial D-loop sequence was amplified by PCR then used for genetic analysis.We detected 11 haplotypes of 2015 samples and 8 haplotypes of2017 samples.The haplotype diversity?h?was 0.857±0.006,and the nucleotide diversity???was 0.0102±0.0055.The genetic diversity was lower than the sample in1995-2000.AMOVA analysis indicated that 91.70%of the genetic variability occurred within each year's juvenile populations.The value of Fst shows a middle genetic diversity between annual samples.3.Population genetic diversity of Chinese sturgeon based on the mitochondrial CO?gene sequenceA 1050 base pair mitochondrial CO?sequence was amplified by PCR then used for genetic analysis.We detected 7 haplotypes of 2015 samples and 5 haplotypes of2017 samples.The haplotype diversity?h?was 0.358±0.021,and the nucleotide diversity???was 0.00037±0.00038.The genetic diversity was lower than other anadromous fish.AMOVA analysis indicated that 94.70%of the genetic variability occurred within each year's juvenile populations,and the value of Fst shows a middle genetic diversity between annual samples.Neutral test shows that the evolution of the COI sequence deviated from the neutral model but was no significant statistically,showing a negative selection effect.