The Study On Growth And Development Of Liza Haematocheila In The Yangtze Estuary Based On Otolith Microstructure

Liza haematocheila belongs to Mugiliformes,Mugilidae,Liza.As a kind of fish being able to adapt to a wide range of temperature and salinities,L.haematocheila is mainly distributed in estuaries and adjacent waters and feeds on phytoplankton and zooplankton,which plays an important role in the matter and energy flow of estuary ecosystem.This research was based on the study of morphology and trace elements of otolith,and the life history and growth condition of L.haematocheila in Yangtze Estuary was analyzed in this work,which was aiming at providing reference and laying a foundation for further studying how L.haematocheila choose and utilize the Yangtze Estuary habitat,and maintaining the species diversity in Yangtze Estuary.Main results of this research are as follows:1.Sagittal otolith morphology and the relationship between its mass and the age of Liza haematocheila in the Yangtze EstuaryIn order to study sagittal otolith morphology and the relationship between its mass and the age of L.haematocheila in the Yangtze Estuary,used 324 pairs of otoliths were extracted and analyzed which were extracted and dissected from 358 L.haematocheila specimens from the Yangtze Estuary from February to June in 2017.The result showed that sagittal otolith’s size and shape changed significantly with the growth of individuals,from regular melon seeds shape outline to long narrow leaf shape and increasing irregular wavy outline The average density of sagittal otolith was 1.52 mg·mm^-2,the average rectangularity was 0.68,the length of sagittal otolith was 0.021%-0.047%of entire body length（BL）,the width was 0.009%-0.021%of entire BL and the mass was0.045‰-0.731‰of the entire body mass（BM）.Otolith length（OL）,otolith width（OW）and otolith mass（OM）were all significantly related to the BL,and the determination coefficient for OW and OM model was the highest（R²=0.928）.The relationship between OMandBLwasbestdescribedbyexponentialregression:OM=0.0009BL^1.8737（R²=0.967）;and the relationships between OM and age（A）,BL and A applied to multinomial regressions,respectively:OM=2.9262A²+4.8437A+2.1894（R²=0.847）,BL=-3.2248A²+102.54A+38.373（R²=0.858）.In addition,OM was linearly dependent with A.The estimated otolith’s ages from the model were not significant variate from the real ages counting from annulus counts.Therefore,OM could be an effectively assisting parameter for age estimation of L.haematocheila.2.Age structure and growth characteristics of Liza haematocheila in the Yangtze EstuaryTo assess the age structure and the change trend of growth characteristics,806specimens of L.haematocheila sampled in the Yangtze Estuary from February,2017 to April,2018 were analyzed.Otoliths were sampled for age determination.Results showed that the L.haematocheila population in the Yangtze Estuary ranged in age from1 year to 6 years,dominated by individuals of 1³ years（90.35%）.The body length-weight relationships were expressed as:W=9E-6L^3.07（n=705,R²=0.9790）for all samples,W=6E-6L^3.1249（n=390,R²=0.9686）for females and W=1E-5L^2.9737（n=180,R²=0.9550）for males.With the t-test,the parameter of b was not significantly different from the constant of 3（P>0.05）,indicating that L.haematocheila grew at a constant speed.The growth parameter values,derived using von Bertalanffy growth equation,were:L_∞=751.591,k=0.214,t₀=0.030 for all samples;L_∞=1369.841,k=0.067,t₀=-0.187 for females;L_∞=743.189,k=0.179,t₀=-0.745 for males.Males reached asymptotic length sooner than females.L.haematocheila displayed an inflexion point in growth rate and growth acceleration of body weight,with parameters,t_i=5.271for all samples,t_i=16.819 for females;t_i=5.343 for males.It showed that the age of inflection point for body weight growth curve was consistent with the least mature age.To better use and protect L.haematocheila resources,fishing should be carried out after the inflection point.And measures should be taken to protect L.haematocheila resources,such as reducing the fishing intensity and protecting the spawning grounds.In previous study,it has been observed that the juvenile fish supplied a large proportion in the Yangtze Estuary,which indicates the estuary a nice habitat for the juvenile.3.Otolith element composition of Liza haematocheila in the Yangtze EstuaryIn this paper,we studied the trace element composition of otolith in L.haematocheila in the Yangtze Eastuary by laser ablation inductively coupled plasma mass spectrometry（LA-ICP-MS）,then deduced the habitat in different life stages.The results indicated that the otolith of L.haematocheila mainly contained 47 elements,and calcium（Ca）,sodium（Na）,strontium（Sr）,iron（Fe）,barium（Ba）,magnesium（Mg）,manganese（Mn）,Chromium（Cr）,zine（Zn）,lithium（Li）were the 10 most abundant elements.Ca was the most stable element in the otolith.The analysis of variance showed that there was no significant difference in each elements distribution between different sex except for Fe and Zn.There were significant differences in the elements of Ca,Na,Sr,Fe,Ba,Mg,Cr and Zn but no significant difference was found in Mn and Li among different ages in the otolith.Even though L.haematocheila stayed mainly in brackish water for growth and development,it could also adapt to seawater/freshwater habitats with higher/lower salinity,suggesting a highly adaptation of a wide range of salinity habitats.In addition,L.haematocheila individuals in this study might be divided into three different life history groups（hatching in the habitats of freshwater,brackish water,and sea water）based on Sr/Ca ratio in otolith cores.Totally,peripheral zone is higher than nucleus in Sr/Ca ratio.The habitat history of L.haematocheila was reconstructed as that low salinity habitats seemed to be required at the stages of earlier development,while the increased salinity habitats seemed to be preferable for the growth and development at the remaining stages of the life history.