The Elemental Fingerprint In Different Stages Of Early Life History And Population Identification Of Small Yellow Croaker(Larimichthys Polyactis)

The element content in the otolith, affected by the temperature, salinity, water element concentration and other factors, shows different characteristics in the process of growth, which is called otolith elemental fingerprint.The elemental fingerprint on otolith is very stable and can reflect the water environment of the whole life stages of fish, which has been widely used in studies such as growth and development in early life history, stock identification, reconstructing migration history of fish.The small yellow croaker(Larimichthys polyactis) is an important fishery resource in china, but there are some questions at the time of the resource recovering. We must take some measures to strengthen the study and protection of the small yellow croaker resources.In view of less studies of early growth and development and the population identification, we plan to use the otolith microchemistry analysis technique to study the otolith elemental fingerprint of small yellow croaker populations in different life stages and in different sites.We aim to delineate the variation pattern of per single element in otolith and discriminating the different populations of small yellow croaker. Both two studies can accumulate the data of otolith microchemistry and provide scientific proposals for the management of small yellow croaker resources.Firstly, we used the LA-ICP-MS element analysis technique to study otolith elemental fingerprint in different development stages of small yellow croaker larvae fish.A total of 5 regions on the otolith(P1, P2, P3, P4, P5) was selected, which formed in the early growth and development stage, to study the otolith elemental fingerprint.From hatching to the juvenile stage, the small yellow croaker experienced different water environment and physiological changes, both the external factors and internal physiological factors can affect the elements aggradation in otoliths.The results of the study show that there is a significant difference of each element content in different developmental stages and there is some certain changing tendency of every element. From larvae to juvenile fish, Sr generally decreased gradually, while Mg, Mn and Ba showed a gradual upward trend.The four kinds of elements content in the otolith core were higher than other growth zones, this may be related to the composition of the structure of calcium carbonate crystals in the otolith primordia.Then we studied the otolith core elemental fingerprint of larvae and juvenile small yellow croaker that sampled in different sites from East China Sea and the Yellow Sea coastal waters.The speciemens were collected in 5 sites, which were Lvsi, Luchao port, Xiangshan, Wenling and Sanmen bay. Site specific microchemical signatures were developed using element:Ca ratios, which were determined with laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) on the otolith core. Microchemical signatures(Li:Ca, Na:Ca, Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca, Zn:Ca) showed highly significant differences among sites(MANOVA, p<0.001). Via linear discriminant function analysis(LDFA) based on elemental ratios(Li:Ca, Na:Ca, Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca), fishes were classified back to sampling sites with 70.6% correction. The classification accuracies of Lvsi was the highest(86.2%), while Wenling was the lowest(58.3%). The Lvsi population in the southern Yellow Sea can obviously be distinguished from other populations, other populations in the East China Sea are mixed together and difficult to distinguish.Finally, based on the research of chapter 2, we analysed the otolith core elemental fingerprint of larva and adult small yellow croaker from same generation that sampled from Lvsi and Sanmen spawning grounds.Our purpose is to explore the possiblity of distinguishing breeding populations of small yellow croaker in different spawning grounds.The result showed that of the 9 kinds of element(Li, Mg, Mn, Co, Ni, Cu, Zn, Sr, Ba)measured in otolith nucleus, Sr element content was the highest, followed by the content of Mg element, other element content was very low.Independent sample T test result showed that there was significant difference of Mn, Co, Zn between the breeding populations of small yellow croaker otolith in different spawning grounds, while other elements had no significant difference. Selecting the elements which had significant difference as the identification elements to use linear discriminant function analysis(LDFA)on the two spawning populations of small yellow croaker.The results showed that the discriminant function F1(characteristic value is 7.19) can distinguish the two breeding populations of small yellow croaker from Lvsi and Sanmen.The discriminant rate was 90.9% and 80%, the overall identification success rate was 85.45%.Of the three identification elements, Co had the largest contribution value, the value was 8.36.By comparing the otolith core elemental fingerprint of larvae and breeding populations, 14 of 22 breeding fishes belong to Lvsi, discriminant rate was 63.6%; 8 of 25 breeding fishes belong to Sanmen, discriminant rate was 32%. The above results indicate that using the otolith elemental fingerprint to distinguish different populations of small yellow croaker is feasible.This study can provide a reference for the population division of small yellow croaker and lay a foundation for the study of migration and population supplement.