东海蓝圆鲹的摄食习性

以2008年5月至2009年2月东海灯光围网采集到的叉长范围为52～276 mm的444尾蓝圆鲹为对象,对其胃含物进行分析,应用K-W非参数检验、卡方检验、聚类分析等方法,对不同季节和发育阶段条件下蓝圆鲹的食性进行了研究。结果表明,蓝圆鲹的摄食种类有80余种,浮游甲壳类(主要包括浮游甲壳类幼体、磷虾和桡足类等)和小型鱼类为其主要食物类群。若按相对重要性指数百分比(IRI%)排序,优势饵料种类最高的是七星底灯鱼(IRI%为40.44%),其次是口虾蛄Alima幼体(IRI%为14.24%)、太平洋磷虾(IRI%为11.26%)等。统计分析检验表明,蓝圆鲹的空胃率和平均胃饱满系数有显著的季节变化和叉长变化(P<0.01),摄食强度春季最高,秋季和夏季相对较高,而冬季最低;叉长50～99 mm和200～299mm的蓝圆鲹的摄食强度较高,其余叉长的强度相对较低。食物组成也随季节和发育阶段的不同而有所变化,在春季主要以七星底灯鱼和口虾蛄Alima幼体为食,夏季主要以甲壳类幼体为食,秋季主要以七星底灯鱼和太平洋磷虾为主食,冬季食物匮乏,小型桡足类丽隆剑水蚤和糠虾类占其食物组成的很大比例。聚类分析的结果表明,蓝圆鲹叉长200 mm是其摄食取向的拐点,小于这个叉长的蓝圆鲹以浮游甲壳类为主,大于这个叉长的以捕食小型鱼类为主,随着叉长的增大,蓝圆鲹更多的以游泳动物为食。根据蓝圆鲹摄食饵料的类群变化,东海蓝圆鲹的营养级为3.55,属于浮游动物和游泳动物混合食性的肉食性鱼类。

Feeding habits of blue mackerel scad Decapterus maruadsi Temminck et Schlegel in the East China Sea

Blue mackerel scad,Decapterus maruadsi Temminck et Schlegel,is an important pelagic species which is distributed in the coastal areas of China.In the present paper,a total of 444 specimens of blue mackerel scad at fork length(FL)of 52-276 mm were sampled from seasonal light-purse seine surveys in the East China Sea from May 2008 to February 2009.By analyzing the stomach contents of Decapterus maruadsi,more information was provided on the East China Sea fish feeding ecology.The results showed that more than 80 prey species were ingested by blue mackerel scad,while planktonic crustaceans and small-scale marine fish constituted the dominant prey groups.Among the crustaceans,planktonic larvae,euphausiacea and copepoda made an important contribution to the diet.At the species level,as indicated by the percentage index of relative importance,Benthosema pterotum accounting for 40.44% was the most dominant prey,followed by the Squillidae alima larva accounting for 14.24%,Euphausia pacifica accounting for 11.26%.The percentage of empty stomachs and mean stomach fullness index,which were analyzed by applying the chi-square test and Kruskal-Wallis test,varied significantly among different seasons and size classes.It indicated that the feeding intensity was the highest in spring and lower in winter.Meanwhile,the feeding intensity was the highest in size classes of 50-99 mm and 200-299 mm while the lowest in other size classes.The major diet composition was significantly different among different seasons and size classes.The B.pterotum and Squillidae alima larva were the dominant prey in spring,whereas the planktonic crustacean larvae in summer,B.pterotum and Euphausia pacifica in autumn,Oncaea venusta and mysidacea in winter.Cluster analysis employing Bray-Curtis similarity index revealed there was an abrupt change in diet composition at about 200 mm FL.The planktonic crustaceans were the dominant prey groups of fish smaller than 200 mm FL,whereas small-size marine fish were the dominant prey for fish greater than 200 mm FL.It indicated that the percentage of nekton significantly increased with the increase of fish size.Compared with the previous studies,the diet composition of D.maruadsi varied significantly,the proportion of B.pterotum decreased markedly.In addition,the average trophic level of D.maruadsi in the East China Sea was 3.55,which was carnivorous fish feeding on plankton and necton.