长江口盐沼植被生境内斑尾刺虾虎鱼食性特征

根据2015年5月至2016年4月在长江口东滩盐沼湿地水域采集的斑尾刺虾虎鱼样本数据,分析了该生境斑尾刺虾虎鱼的生物学和食性特征。结果表明:共采集到斑尾刺虾虎鱼186尾,其中6—8月采集的数量较高,而其他月份较低。约96%个体为幼体(平均体长109 mm),平均摄食等级为1.5。斑尾刺虾虎鱼主要摄食虾类(IRI(%)=69.05)、鱼类(IRI(%)=17.31)、蟹类(IRI(%)=11.51)和双壳类(IRI(%)=0.95)等11大类41小类饵料生物;虾类作为最重要的饵料类别,其生物量、数量和出现频次百分比均排列第一,以安氏白虾(Exopalaemon annandalei)、日本沼虾Macrobrachium nipponense)、长额刺糠虾(Acanthomysis longirostris)等虾类为主要饵料。鱼类饵料中,以大鳍弹涂鱼(Periophthalmus magnuspinnatus)、大弹涂鱼(Boleophthalmus valenciennes)等虾虎鱼科鱼类为主要饵料。各月平均饱满指数P(%)波动较大,6—11月呈逐渐增加趋势。随着体长的增加,饵料组成中鱼类的比例呈逐渐增高趋势,成体个体的饵料中鱼类的生物量比例达65%以上,虾类的比例则下降明显。6—8月斑尾刺虾虎鱼白天样本中鱼类饵料的重量百分比显著高于夜晚(P0.01),约是夜晚的8倍;但虾类则是夜晚显著高于白天(P0.01),约是白天的2倍,而蟹类饵料的昼夜差异不显著。从等级聚类(即组平均法)的分类方法可知,斑尾刺虾虎鱼各体长组食物组成在10%相似性水平上可分为3类,即41—60、61—180 mm和181—200 mm。从营养生态位宽度来看,41—60 mm体长组生态位宽度值为0.86,而61—120 mm体长组随着体长的增大而增大,但121—160 mm体长组生态位有所降低。盐沼生境丰富的饵料环境为斑尾刺虾虎鱼提供了良好的摄食场所,同时盐沼植被茂密的植株也可为幼体提供躲避捕食者的最佳庇护所,初步证明盐沼对于斑尾刺虾虎鱼具有重要的生境价值。

Feeding habits of Acanthogobius ommaturus in the salt marsh in the Yangtze Estuary

To analyze the biological and dietary characteristics of Acanthogobius ommaturus, a total of 186 individuals were collected in the salt marshes in the Yangtze Estuary from May 2015 to April 2016, with the highest abundance collected occurring in the summer (June, July, and August). About 96% of the total specimens were young fish with an average body length of 109 mm and an average feeding level of 1.5. The prey items included 11 groups and 41 species dominated by shrimps (Index of Relativity Important, IRI (%)=69.05), fishes (IRI (%)=17.31), and crabs (IRI (%)=11.51). The dominant species of shrimp prey items were Exopalaemon annandalei and Macrobrachium nipponense, and of fish, Periophthalmus magnuspinnatus and Boleophthalmus valenciennes. The mean stomach fullness index P (%) varied, and increased slowly from June-November. The proportion of fish prey items increased with increasing length, whereas the biomass proportion of fish prey items in adult species was above 65% and increased with increasing body length Food composition of Acanthogobius ommaturus was analyzed for differences in the day and night from June-August. The weight proportion of fish prey items during the day was 8 times higher than at night (P < 0.01), whereas for shrimp, weight proportions were 2 times higher at night than in the day (P < 0.01). There was no significant difference for crabs between the day and night. Three body length groups (41-60 mm, 61-180 mm, and 181-200 mm) were identified for Acanthogobius ommaturus individuals at the 10% similarity level analyzed by CLUSTER. For the trophic niche of Acanthogobius ommaturus in each size class, the trophic niche in the 41-60 mm group was 0.86. By contrast, the trophic niche increased in the 61-120 mm group, and decreased in the 121-160 mm group. Therefore, the rich food environment in the salt marsh supplies a good feeding place for Acanthogobius ommaturus, and the dense plants can supply the best shelter for young fishes. These can help young fishes grow to adults in the autumn, and can then move to deeper waters for the winter. In conclusion, our study preliminarily indicates that the salt marsh plays crucial roles in the development of Acanthogobius ommaturus.