长江口凤鲚仔稚鱼不同发育阶段矢耳石生长

2014年4—8月于凤鲚(Coilia mystus)的主要繁殖期在长江口采集仔稚鱼103尾。分析凤鲚仔稚鱼样本得出日龄范围为5~48 d,体长为4.20~26.21 mm。为研究长江口凤鲚早期发育不同阶段生长,测定了凤鲚仔稚鱼(5~48日龄)体长随日龄的生长变化,其变化分为3个阶段(5~11日龄、12~30日龄、31~48日龄)。不同日龄阶段,体长的生长速率差异性显著(P0.05)。耳石早期发育研究发现耳石长、耳石宽随鱼体的生长而增长,在17~19日龄之后其生长速率增大约2倍。采用分段回归方法分析耳石长、耳石宽与日龄的关系,发现二者异速生长的拐点均出现在19~20日龄,拐点前为慢速生长,之后为快速生长。研究发现凤鲚早期生长发育阶段的耳石形态有较为显著的改变:卵黄囊期、前弯曲期为圆形;弯曲期耳石长的生长大于耳石宽的生长,耳石逐渐变成椭圆形;耳石变成稳定形态后,长宽比基本保持稳定。

Sagittal otolith growth and development at different development stages in larval and juvenile Coilia mystus in the Yangtze estuary

Coilia mystus is a very important commercial fish distributed widely in the Yangtze estuary. It is a mi-gratory species which grows and matures in the coastal waters and then naturally migrates into the Yangtze estuary for spawning. Otolith growth and development at different stages in larval and juvenile C. mystus can help to un-derstand their characteristics under natural conditions. An understanding of otolith early growth and development is essential not only for wild population conservation but also for artificial seeding production. In this study, a total of 103 larval and juvenile C. mystus were collected in the Yangtze estuary, from April to August in 2014. Otolith analysis revealed that the age of specimens ranged from 5 to 48 days. To study the early growth and de-velopment of different stages, the body length of 103 individual C. mystus was measured. Statistics showed that the cubic function best described the increase of body length with age. The increase of body length can be divided into three stages, 5-11 d, 12-30 d, and 31-48 d. The growth rate was significantly different among these stages (P<0.05). To study the morphological development, the otolith length and otolith width were measured, and the analysis showed that the increase of otolith length and width increased with body length. After 17 to 19 days, the growth rate increased by about 2-fold. Piecewise regression analysis between otolith length, width, and otolith age was carried out in order to determine the allometric growth pattern, and the inflection point of otolith length and otolith width both occurred at 19-20 days. The growth rate before the knot was slow, while it was rapid after the knot. The otolith morphology of C. mystus changed significantly at different stages in the early life history. The otolith is circular in the yolk-sac and preflexion stages. Otolith length growth is greater than that of otolith width in the flexion stage, and the otolith becomes oval. After the form becomes stable, the ratio of otolith length and width also remains stable.