黄海中部近岸产卵场日本鳀卵子大小的时空变化

Spatial and Temporal Changes of the Egg Size of Japanese Anchovy(Engraulis japonicus)Inhabiting the Near Shore Spawning Ground of Central Yellow Sea

2013年4月下旬至7月上旬,在黄海中部近岸产卵场20m以浅水域进行6个航次的鱼类浮游生物调查,对日本鳀(Engraulis japonicus)卵子形态及大小的时空变化进行研究。结果表明:调查海区日本鳀卵子形态呈椭球形,卵子大小在不同发育阶段无显著性差异,但其时空变化差异显著。从5月上旬至7月上旬,卵子大小整体上呈逐渐减小的趋势,且与水温呈显著负相关。日本鳀卵子在调查海区最早出现于5月上旬,卵子最大,长径(1.57±0.09)mm,短径(0.77±0.04)mm,纵切面积(0.95±0.07)mm2;6月下旬卵子最小,长径(1.20±0.07)mm,短径(0.64±0.03)mm,纵切面积(0.61±0.43)mm2。同历史数据相比,调查海区的日本鳀卵子5月上旬显著大于东海海域,6月下旬显著小于山东半岛南部。

The Japanese anchovy Engraulis japonicas is widely distributed along the western North Pacific,such as eastern China Sea,Yellow Sea,Japan Sea,etc.and it has also supported one of the largest fisheries in China over the last three decades with the peak yield of more than 1million tons in 1990 s.However,there are few studies for the early life stages of this species in North Pacific,especially in near shore spawning ground of central Yellow Sea.Egg size of fish is not only easy to quantify,but also often reflects the amount of resources mothers invest in individual offspring.It is treated as one structural element with which to characterize a species＇ ontogeny regardless of causal relationships between the species and its habitat.It is therefore that egg size often highly varies both between different species and between stocks of a species,even between clutches of the same individual.As shown by numerous publications dealing with conditions of life and reproduction of fishes,egg size of fish is an important biologi cal parameter characterizing the environment of spawning ground and fish reproductive traits.This study were aimed to as follows：1）report changes in egg size throughout the Japanese anchovy spring and summer spawning season as well as the spatial characteristic of egg size in near shore waters of central Yellow Sea;2）evaluate whether egg size varies with respect to space and time,and 3）provide data for studies on its reproductive traits and resources variation mechanism.Six ichthyoplankton cruise surveys were conducted in 〈20 mdepth waters of central Yellow Sea from late April to early July,2013 with the time interval of half a month.We collected Japanese anchovy eggs from 75 stations along the coastal zone（34.5°N^35.5°N,119.0°E^120.5°E）.This area is one important part of the spawning waters of Japanese anchovy.Eggs were collected with a plankton net（500μm mesh）.Upon collection,all eggs were preserved in 5% buffered formalin and then transferred to the lab after the survey.Egg size（length,width,area）was measured by software Image-Pro Plus 6.0based on the images captured on a dissecting microscope and camera（Nikon SMZ1500）.Based on data from the six cruise surveys conducted,the temporal and spatial changes in the morphology and size of Japanese anchovy eggs were investigated.The results indicated that the morphology of elliptical anchovy eggs was similar among anchovy eggs at different developmental stages.However,egg size varied temporally and spatially.Egg size decreased generally from early May to early July,which was negatively correlated with water temperature.The eggs began to occur in the study area in early May with largest longitudinal section area of（0.95±0.07）mm2（longer axis（1.57±0.09）mm and shorter axis（0.77±0.04）mm）.Minimum egg size occurred in late June（longitudinal section area（0.61±0.43）mm2,longer axis（1.20±0.07）mm and shorter axis（0.64±0.03）mm）.Compared with the documented previously,Japanese anchovy eggs from early May in the currently studied area were significantly larger than those collected in coastal waters of East China Sea,and anchovy eggs from late June were significantly smaller than those collected at the spawning grounds off south Shandong Peninsula.These results is consist with the popular science regularity that egg size varies among different spawning grounds and decreases during the whole spawning season.In the meanwhile,the phenomenon that there were some spatial egg size varies to be founded between positions in so small areas would be paid more attention to it.