Interrelationship among daily age, body length, birth date and sampling loaction at recruitment of Anguilla japonica elvers in the Chinese coast

A total of 191 Anguilla japonica elvers,collected at 6 locations along the Chinese coast were observed in order to determine age and to measure body length.The average length of elvers at 6 locations ranged from (53.4±2.2) to (58.1±1.7) mm(X±S.D).There were no relationship between body length and location of elvers distribution.The average daily ages of elvers at 6 locations ranged from (138.2±6.7) to (155.2±9.0) d(X±S.D).The maximum radius,check around the nucleus,average growth increment width and the changes of the increment width of otolith were compared.The average radius of otoliths of elvers at 6 locations ranged from (142.5±8.4) to (155.8±14.5) μm(X±S.D).The average maximum diameters of the check around the nucleus of the otoliths ranged from (10.36±0.85) to (10.81±1.26) μm (X±S.D),there was no significantly different among them (p>0.0l).The average increment width of otoliths ranged from 0.996 to 1.097 μm,there was significantly different among them (p<0.0l).The growth rate of the otolith was the highest at Wenchou and the Changjiang Estuary.The growth rate of the otoliths declined gradually at other locations towards both lower and higher latitude,respectively.The increment width of the otoliths was the highest at approximately 90-days old at 6 locations.The average daily ages of elvers at the Changjiang Estuary and Wenchou were the youngest.The daily ages of elvers declined gradually at other locations towards both lower and higher latitude respectively while the position of Wenchou and the Changjiang Estuary was the center at 6 locations.Estimated birth date based on the daily ages at 6 locations ranged from 15 August,1993 to 10 Janaury,1994.The individual at lower latitude is earlier birth but no younger,and recruit earlier.