摘要
鉴定刀鲚年龄的方法很多。本文以鳞片为主,对照耳石、胸鳍鳍条等方面的材料,做了比较全面的研究。发现它们都有明显的年龄标志,但各有优缺点。其中以鳞片取材最容易,观察最方便,缺点是年轮标志比较复杂,有时还有副轮和幼轮等。再生鳞也比较多。刀鲚鱼苗和幼鱼在生长过程中,体长增加较快,至11月份,幼鱼最大个体可达200毫米左右。成鱼体长增加速度逐渐减慢,最大个体只410毫米。但随着年龄的变化,其体重却有显著增加。刀鲚鳞片的生长和体长的增加基本上成正比关系。刀鲚寿命不长,一般只有4-5冬龄,最大个体不超过6冬龄。
Age-determination based mainly on scale-reading has been made on the Chinese anchovy, Coilia ectenes Jordan et Seale, from the estuarine region of the Yangtze, the Yangtze River proper as well as certain tributary lakes. The characteristics of the annuli on the scale are described. Structures other than the scales, such as the otoliths, the pectoral fin rays and the vertebrae of this fish are also studied for comparison. Formation of new circuli peripheral to the existing annulus of the scales occurred any time from March through December.The fry and the young fish grow rapidly in body-length, the largest individual reaching 196 mm in November of the year. Among the adult fish examined, the largest female had a body-length of 410 mm, weighing 360 g, 4 years of age; the largest male was 400 mm in body-length, weighing 235 g, and 4 years old too. The minimum sizes of sexually mature individuals were: female 96mm, 6g; male 117mm, 6g; both being one year of age.The ratio between scale-radius and body-length for different age groups is nearly constant.The span of life of this anchovy is 4 to 5 years in general. No individuals upward of 6 years of age ever occurred in our collections, which contained over 4000 specimens intended for age-determination.
