| Coilia mystus commonly is known as seed squid,roast cocktail,anchovy,small squid which belongs to Clupeiformes,Engraulidea,Coilia.It is distributed in China,Korean Peninsula and Japan.C.mystus has delicious taste,delicate meat and high nutritional value.Its canned products have been one of the most important export products in China and enjoyed a good reputation at home and abroad.As the main economic fish and fishing target in the Yangtze Estuary,C.mystus was one of the five famous fishing seasons in the Yangtze Estuary,accounting for 48.6% of the total fishery catch in the Yangtze Estuary.However,due to the impact of climate change and human activities,the amount of Anchovy Resources in the Yangtze Estuary has declined sharply.At present,there is almost no fishing season in the Yangtze Estuary.Conservation and management of Anchovy stock is very important.Based on individual morphology,otolith microstructures and microchemistry,this study was conducted to provide scientific and technological support for the conservation,utilization and scientific management of the resources of the anchovy in the Yangtze Estuary and its adjacent waters.The main results are as follows: 1.Analysis of morphological variations among four different geographic populations of C.mystus in Yangtze Estuary and its adjacent sea areaIn order to study morphological difference of C.mystus distributed in Yangtze River Estuary and its adjacent waters,a total of 160 samples of C.mystus were collected from Lvsi(Ls population),Chongming island of Shanghai(Cm population),Zhoushan(Zs population)and Wenzhou(Wz population).Eleven traditional morphological measurable traits and 19 frame structure data were obtained,which were transformed into 29 morphological proportions.And these proportions were analyzed by multivariate statistical analysis.Non-parametric test analysis showed that there were significant differences in the proportion of other characters of four populations except SL/BL.Principal component analysis constructed seven principal components reflecting morphological characteristics information,among which principal component 1,principal component 2 and principal component 3 played the main roles,and the contribution rates were 44.27%,16.31% and 8.36% respectively and the cumulative contribution rate was 68.94%.The results showed that STL and TL were the main factors affecting the morphological difference of the four populations.The discriminant equations of 4 populations were constructed by using eight parameters which had the largest contribution rate.The discrimination accuracy of Wz population was the highest,reaching 90%,followed by Ls population(87.5%),Cm population(67.5%)and Zs population(60.0%).The comprehensive discriminant accuracy rate was 76.3%.Cluster analysis showed that the Cm and Zs population were the closest to each other,which first clustered into a group,then clustered into a large group with Ls population,while Wz population clustered into a single group.It showed that the morphology of Cm population was closest to that of Zs population,which was significantly different from Ls population and Wz population,and the difference increased gradually.2.Study on differences of otolith morphology of C.mystus populations in the Yangtze Estuary and its adjacent sea areaIn order to study the morphological differences of sagittal otoliths in the populations of C.mystus in the Yangtze Estuary and its adjacent waters,240 C.mystus were collected from the coastal waters of Lvsi(Ls population),Chongming island of Shanghai(Cm population),Zhoushan(Zs population)and Wenzhou(Wz population)respectively.Twenty-one morphological parameters were measured by traditional otolith measurements and otolith frame method.Twenty-one morphological parameters yielded 20 morphological index data which were analyzed by multivariate statistical analysis.Independent sample t-test showed that there was no significant difference in the left and right otoliths among the four populations.One-way ANOVA and non-parametric test showed that there were significant differences in 17 morphological indices among the four populations.Principal component analysis constructed seven principal components reflecting the morphological characteristics of otoliths,with a cumulative contribution rate of 86.31%.The contribution rates of principal component 1,principal component 2 and principal component 3 were 24.56%,19.88% and 13.06% respectively.The results showed that the degree of otolith roundness and the regularity of external contour were the main factors affecting the otolith morphological difference of the four populations.The discriminant equation of four populations was constructed by using nine parameters with the greatest contribution rate.The discriminant accuracy of Wz population was the highest(96.7%),followed by Cm population(66.7%),Ls population(60%)and Zs population(58.3%).and the comprehensive discriminant accuracy was 70.4%.Cluster analysis showed that the Cm and Zs population were the closest to each other,which first clustered into a group,then clustered into a large group with Ls population,while Wz population clustered into a single group.It was concluded that the shape of sagittal otolith in Cm population were similar to that in Zs and Lv population,and the similarity decreases gradually and there were significant differences in the morphology of sagittal otolith between above three populations and Wz population.3.Habitat history reconstruction of C.mystus from Yangtze Estuary and its adjacent sea areaIn order to study the habitat history of C.mystus in the Yangtze Estuary and its adjacent sea area,otolith microchemical analysis of ten C.mystus of Chongming island of the Yangtze Estuary and its adjacent Lvsi sea area was carried out by using X-ray electron probe microanalysis technique(EMPA).Quantitative line analysis and surface distribution of Sr content showed that Sr/Ca ratios in the otolith core area of C.mystus existed Sr/Ca<3,3<Sr/Ca<7 and Sr/Ca>7,and the corresponding concentric rings were blue,green and yellow-red in the analysis of the core surface of otolith.Based on this,it was inferred that the incubation sites of C.mystus could be divided into three types: freshwater incubation field,estuarine brackish water incubation field and sea water incubation field.The variation of Sr/Ca ratios in the individual otolith from the core to the edge was very significant,including low-ratio freshwater habitat(Sr/Ca<3,minimum 2.04±0.87)and high-ratio seawater habitat(Sr/Ca>7,maximum 7.81±0.91).The habitat history types of C.mystus could be divided into four types: freshwater-estuarine brackish water type,estuarine brackish water settlement type,estuarine brackish water-seawater type and freshwater-estuarine brackish water-seawater type.There were freshwater and estuarine brackish water hatching individuals whose habitat types included freshwater-estuarine brackish water type,estuarine brackish water-seawater type and freshwater-estuary brackish water-seawater type in the adjacent sea area of the Yangtze Estuary.There were sea water and estuarine brackish water hatching individuals whose habitat types included freshwater-estuarine brackish water type,estuarine brackish water settlement type,and freshwater-estuary brackish water-seawater type in the Chongming island sea area of the Yangtze Estuary.This reflected the similarities and differences between the individuals in Chongming island and Lvsi sea area in the Yangtze Estuary.Through this study,it is proved for the first time that there are three incubation sites and four habitat types in the Yangtze Estuary and its adjacent sea area,which accurately reflect the diversity and complexity of the individual composition and life history of C.mystus. |
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