Reconstructing Life History Processes Of Electrona Carlsbergi Based On Morphology,Ageing And Microchemistry Of Otolith

Electrona carlsbergi is one of the richest Myctophidae resources in the Southern Ocean.Because of its huge resources and its role as a hub and spoke in the middle and upper reaches of the Southern Ocean,it has important scientific and ecological value.Fish otoliths are formed from the embryonic stage of fish and deposited as the seasonal changes occur.During the deposition process,there were multiple factors such as water environment and water temperature,and there was no reabsorption.The complete life history of fish was recorded.Therefore,otolith can not only be used as a material for the identification of fish ages,but also an analysis of the environmental characteristics experienced in the life history of fish,reflecting the living environment of fish,and effectively inferring the migration path of fish during its life history.In this study,the elliptical Fourier analysis method was used to analyze the shape of the Electrona carlsbergi sagittal otolith.The characteristics of different shapes of Electrona carlsbergi were studied preliminarily.The von Bertalanffy growth equation was used to study the age and growth of Electrona carlsbergi.Using the three data of total concordance,coefficient of variation and average percentage error to quantify the accuracy of age interpretation results.Finally,the longitudinal sections of otoliths were utilized for element signatures analysis using laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).The differences in microchemical composition at the same sampling point for different samples and the differences in the microchemical composition at different sample points in the same sample were compared.Through research,the main conclusions are as follows:1)The otolith of E.carlsbergi were classified into four types based on the morphological characteristics,and 77 Fourier feature coefficients of four types were analyzed by elliptical Fourier analysis.Based on the pairwise comparison on Fourier feature coefficients of four types,the proportions of pairs of coefficients which had significant differences accounted for 61.0%(highest)and 28.6%(lowest)of the total,respectively.2)Based on the Principal Component Analysis(PCA)of 77 Fourier coefficients,the cumulative contributed rate of first 22 principal components was 76.5%.17Fourier feature coefficients were selected to conduct the stepwise discriminant analysis (SDA),and the total discriminated rate was 87.2%.3)Four types for E.carlsbergi’s otolith which appeared on various fish sizes and body masses indicated that the appearance of otolith types was stochastic.The types of otolith were not consistent in the left and right otoliths,indicating different types occurred between both sides of the otoliths.4)Types I and II were the main forms of E.carlsbergi otoliths,accounting for 72.6%of the total,while types III and IV were the secondary forms,accounting for 27.4%of the total.5)Rings on the section that polished cann’t display on the same plane at the same time, because of the core is rised and excisural notch is sunken.it affected age of reading, because of the rings on transverse section were not clear and numerous vice and false wheel structures.6)On the final age determined,the values of 3 indexes that TC,CV and APE were 66.35%、4.98±0.86%and 3.52±0.61%.7)The VBGF function of Electrona carlsbergi is as follow:L_t=79.3639(1-e-0.4101(t+3.6191).8)The samples can be divided into two classes,according to the difference of Sr/Ca ratio in the nucleus.There are mainly two possible reasons for the difference in Sr/Ca ratio:one reason is that there are different hatcheries,another reason is that there are different spawning seasons although the hatchery in the same area.The trend of Sr/Ca ratio on other age groups may be due to acrossing ocean fronts.9)It can be speculated that the spawning ground of Electrona carlsbergi may be located in sub-Antarctic Zone,according to the ocean fronts in ACC system and the trend of Sr/Ca ratio in each age group.After that Electrona carlsbergi was carried by eddies to the the warmer water where near Subtropical front for hatchering.Electrona carlsbergi migrated across sub-Antarctica Front to Antarctic Polar Frontal Zone before age 1.Then individuals migrated across Antarctic Polar Front into Antarctic Zonne around age 2.Finally,individuals were distributed in the Antarctic Zone after age 2.After spawning,the adult individuals and eggs have different migration routes.The adult individuals migrated south into Antarctic Zone,while eggs migrated north into hatchery.