Studies On Otolith Morphomentry And Microchenmistry Of Coilia Nasus Collectde From The Jiangsu Section Of The Yangtze River

The Yangtze River is the largest river in China and occupies an important position for Chinese freshwater fishery.There are very rich migratory fish resources,including a high economic value fish estuarine tapertail anchovy(ETA)Coilia nasus.The research of this species becomes a hot hotspot recently.As a traditionally famous and precious fish,C.nasus is recognized as one of the three most delicious fish of the Yangtzr River with Tenualosa reevesii and Takifugu obscurus.However,in recent years due to overfishing,water conservancy construction,habitat destruction and other anthropogenic impacts,there has been a sharp decline in the resource of C.nasus,and tendency of miniaturization and lowering age has occurred in this fish.Consequently,the research on resource conservation and habitat evaluation of C.nasus is urgently needed to strengthen.As one of the main fishing areas,population size of C.nasus in the Jiangsu section of the Yangtze River always attracts a lot of attention.Moreover,although limited fishery seasons of C.nasus are set in the section by government,the effect is still needed to evaluate.It is noteworthy that both long upper jaw ETA(C.nasus)with high cemmcial value and short upper jaw ETA(once named as C.brachygnathus)with low cemmcial value distribute in the Jiangsu section of the Yangtze River.There have been dispute so far about the taxonomic status of the two ecotypes,although the current idea believes that the above types of ETA are diadromous and freshwater resident ecotypes of C.nasus,respectively.According to traditional discriminant method,the length ratios of upper jaw to head are>1 and<1 for the former and latter,respectively.However,it is still necessary to reliably verify the feasibility and practicality of the traditional experience method.At present,it is difficult to completely retrieval habitat history and migratory patterns of diadromous fish by traditional capture and molecular approaches,thus more effective methods should be introduced so as to discriminate the population composition and reconstruct life history objectively.Recently,study of otolith microchemistry and microstructure has been growing in China,which can provide us a corresponding effective route.Generally,otolith microstructure is used to discriminate fish age and population,while that of microchemistry is used to retrieval fish habitat requirement during life history.Noteworthyly,the deposition variations of strontium(Sr)and calcium(Ca)are often recognized as inversion of fingerprints that present different sanility habitats.The content of Sr and Ca in otolith possibly illustrates and labels the chemical characteristics of different water habitats during the process of fish migration.Therefore,the otolith Sr:Ca ratio and especially Sr content are usually regarded as the effective elemental habitat fingerprint to reveal mysteries of fish migratory ecology.Based on the above advances,technologies of otolith microchemistry and microstructure will be utilizated in this work to study the ecotypes,life history traits,resource compositions and habitat requirements of C.nasus collected from the Jiangsu section of the Yangtze River,including sections of the Nantong,Changshu.Jingjiang and Nanjing.It is hoped to provide theoretical basis and technical support to accurately learn about the migration and habitat useage,and,thus,objectively evaluate the migratiory ecological charcterastcs of the two ecotype resources of C.nasus with different commercial values among different sections of the Yangtze Rive in Jiangsu province.The main results of this dissertation are the following:1.A microstructure study was carried out,using a truss network of 11 distance measurements,on the morphological characteristics of the sagittal otoliths in long upper jaw ETA(except for special declaration,C.nasus is referred to as long upper jaw ETA,similarly hereinafte)and short upper jaw ETA,as well as C.nasus among different sections of the Yangtze Rive in Jiangsu province.Significant morphological differences were observed between long upper jaw ETA and short upper jaw ETA.Discriminant function analysis allowed correct classification rate of 100%for the former vs.the latter.In contrast,those differences were not clear among C.nasus among four different sections of the Yangtze Rive in Jiangsu province,implying a possible connectivity among the C.nasus resource groups in these riverine sections.2.A microchemical study was carried out in C.nasus from Nantong section of the Yangtze River by an electronic probe microanalyzer(EPMA).All otolith samples were divided into two microchemical patterns,i.e.,one was that otolith Sr/Ca ratios(namely Sr/Ca×103,similarly hereinafte)were uniformly in the low value(<3.0),and another was that otolith Sr/Ca ratios changed complex which can be divided into several phases.The fish with the former freshwater pattern were just or less than 1 year old,which was unable to determine whether they would move downstream into estuarine brackish or sea habitats in their later life stages.But the fish with the latter diadromous pattern obviously participated an anadromous migratory and experienced the shift between freshwater and estuarine brackish habitats.3.Otoliths were used to take microchemical analysis of EPMA,of C.nasus collected from the Changshu section of the Yangtze River.Amongest 13 C.nasus sampled in 2007,the Sr/Ca ratios of 12 long upper jaw ETA were consistently low(≤2.00),reflecting a freshwater resisdent history in their life cycles.Contrastly,the otolith Sr/Ca ratio of remaining one long upper jaw ETA(07CSCE13)fluctuated obviously,showing a typical diadromous life history,i.e.,not only a low phase of freshwater(1.51 ±0.85),but also the the high phases of brackish water(4.92±0.63),and even sea water(7.30±0.79).Similarly,the 3 long upper jaw ETA collected in 2009 were all typical diadromous C.nasus.This present study found,for the first time,that coexisting freshwater resident and anadromous long upper jaw ETA in the Changshu section and some long upper jaw ETA of the Yangtze River(e.g.,Changshu section)were possibly able to reside whole life history in freshwater habitat.Namely,the aforementioned length-based experience approach of upper jaw will not always correct for separating high value diadromous C.nasus from low value freshwater resident C.nasus.4.In order to explore the difference in the life history of tapertail anchovy between its Coilia nasus and C.brachygnathus ecotypes which live in Jingjiang section of Yangtze River,an EPMA was applied to analyze the microchemical patterns of element Sr and Ca in otoliths of these two ecotypes collected from Jingjiang section of the Yangtze River.The analysis results of line transect showed that the Sr/Ca ratio in the otolith of C.brachygnathus was consistently low(around 2.0)throughout the otolith,indicating that these individuals experienced in freshwater habitat during its whole life.In contrast,C.nasus had a fluctuation pattern of Sr/Ca ratio from low to high in the otolith,suggesting the individuals experienced not only the freshwater,but also the brackish water at different stages in their life history.All these differences could be well confirmed by the freshwater coefficient(FC).The value of FC in the C.brachygnathus is 1.00±0.00,and contrastly,the values of Fc in the Coilia nasus are 0.36±0.06 and 0.50±0.11 for the individuals collected in 2013 and 2014,respectively.It confirmed an obvious difference of life history between C.nasus and C.brachygnathus,as well as C.nasus collected between different years.The present study demonstrated that the migration pattern of C.nasus and C.brachygnathus were significantly different.Meanwhile,there might be several C.nasus groups in Jingjinag section with different freshwater and brackish habitat phases.The Jingjinag section of Yangtze River must be important migration channel for both ecotypes of tapertail anchovy.5.To further understand the migration characteristics of C.nasus,an EPMA was applied to analyze the microchemistry patterns of element Sr and Ca in otoliths of ten long upper jaw ETA collected from Nanjing section of the Yangtze River in 2009 and 2014.The results of line transect analyses showed that the Sr/Ca ratio in the otolith of the anchovies could be divided into two types:(1)Sr/Ca ratio had a fluctuation pattern between low(<3.0)and high(>3.0)phases in the otolith,suggesting the individuals were anadromous ecotype which experienced not only the freshwater,but also the brackish water,even the sea water at different stages in their life history.(2)Sr/Ca ratio was consistently at low phase(<3.0)throughout the otolith,indicating that the individuals only experienced freshwater habitat during their whole life history.These evidences were supported by the Sr mapping analyses.The results found,being similar to those aforementioned of C.nasus from the Changshu section,that long upper jaw ETA could be the ecotype individual of freshwater resident,although it is traditionally believed that all of them in the Yangtze River were diadromous ecotype.The freshwater resident C.nasus with low commercial value and the diadromous C.nasus with high commercial value cannot be effectively distinguished from each other only by the upper jaw length of C.nasus.