Research On Early Life History Of Anguillajaponica Temminck Et Schlegel Recruitment In Yangtze Estuary

Catadromous eel Anguilla Japonica is widely distributes in rivers，lakes andoffshore in East Asian of Philippine，Taiwan，coastal of Mainland China，KoreanPeninsula and Japan. It’s spawning in waters west Mariana Islands，east of Philippines.Every year, the newly hatched leptocephali drift with the current to the recruitmentplace of East Asian，during this period，they metamorphosis into glass eel. After ashort life at estuary，they migrate into freshwater rivers， lakes and live for about5-8years until approaching sexual maturity，then they be gan it’s migration for about2000miles to their spawn area. During the recent decades，the resource of Anguillideels facing continuous decreasing，and researches suggest fluctuation of Japanese eelAnguilla japonica recruitment stock due to ocean environment changes，climatechanges in Northern Hemisphere such as El Nino and habitat lost caused by humanactivities. In order to investigate the impacts of those factors，the early life history ofJapanese eel Anguilla japonica recruitment must be characterized. In this paper, westudy the samples collected from January2011to April in Yangtze Estuary， analysismorphological characteristic，growth pa ttern，daily age and otolith microstructure toprovide basic information about early life history of Japanese eel Anguilla japonica.1.The normal distribution pattern of samples total length is bimoda l withmaximum6.21cm，minimum5.21cm，mean total length5.80cm.The mean bodyweight of samples is0.130g， with maximum0.241g， minimum0.056g.Lineardistribution can be found between total length and body weight. The sample’s bodyweight in March and April was significantly higher tha n in January and February，suggested that growth was inhibited at low temperature during January and February，in addition nutrition condition in March and April was much better than that inFebruary and January. Mean Long-axis radium of samples is153.01μm， withmaximum174.92μm， minimum131.55μm， normal distributed， mostly between144μm-166μm，no significant differences has been found between each month.39samples daily age had been determined，mean daily age is145.33±14.69old，withmaximum183， minimum117， normal distributed， mostly between127-167， nosignificant differences has been found between each month.2.Mean total length daily growth rate is0.0401cm/d，with maximum0.0480cm/d，minimum0.0334cm/d. Mean otolith daily growth rate is1.06μm/d，withmaximum1.297μm/d， minimum0.833μm/d. Negative correlation can be foundbetween daily age and both total length daily growth rate and otolith daily growthrate.，means that growth fast migration to recruitment place first，or the younger the faster it growth. It indicate that it’s growth inhibited during this period，coincidencewith Gompertz growth pattern，and the eels requires migrate to freshwater to continuetheir growth.3.The otolith can be divided into four section according to otolith daily growthincrement widt h：1.the first section，the first20-30increments closed to nuclear，thewidth of increment increased gradually；2.the second section，from about the30th toabout the60th increment，the increment width is narrow；3.the third section，fromabout the60th to about the120th increment，the width of the increment increasedgradually；4.the fourth section，the left peripheral increment to the edge, the incrementbecome narrow.4.The otolith microstructure could part into3layers observed by metallographicmicroscope BX-51M：1.Nuclear， the dark nuclear at the centre of the otolithsurrounded by a dark ring called Hatch Check which account abo ut10μm diameter，at the outer lies a dark mark which considered as first feeding check；2.The secondlayer，this layer was composed of a series of narrow growth increments，ended atmetamorphose check；3. The last layer， the growth increments outside themetamorphose check，the growth increments were narrow and diffuse，barelydiscernible，this layer correspond to estuary life after metamorphos is.5.It can be found several dark checks at the otolith under metallographicmicroscope BX-51M，each check actually composed by3or4growth increments.4checks identified until now：The hatch check （HC），a dark groove close to nuclear；first feeding check（FFC），a dark mark formed by3or4growth increments；metamorphose check（MC），the mark where growth increments increased drasticallyand elver mark（EM），which indicates the larvae entering freshwaters，we didn’tfound this mark during this study.