Investigation on shrimp feeding of <i>Coilia nasus</i> during its anadromous migration along the Yangtze River

Abstract

刀鲚（Coilia nasus）是长江的名贵经济鱼类.虽然传统上认为其溯河生殖洄游全过程不会摄食，但该问题一直尚未完全弄清.作为有效解明这一问题的第一步，本研究在前期长江流域干流和湖泊刀鲚资源调查的基础上，先利用耳石微化学技术筛选出长江河口区、江苏江段、安徽江段和鄱阳湖水域溯河洄游型的刀鲚个体，再对其胃、肠容物的大型游泳动物（鱼、虾类）进行调查分析.结果发现，在河口区、江苏和安徽江段所有刀鲚个体胃充塞度为0级，均未发现摄食有游泳动物；而鄱阳湖水域刀鲚个体的胃充塞度达4~5级，均发现有摄食淡水虾类的日本沼虾（Macrobrachium nipponense）和秀丽白虾（Exopalaemon modestus）的情况.其中29%和71%的刀鲚胃中分别含有1只和2只虾.所有刀鲚个体肠内均未发现有内容物.鉴于鄱阳湖已被确定为溯河洄游型刀鲚的产卵场之一，结果表明长江刀鲚在经河口，通过长江江苏和安徽江段干流到达鄱阳湖产卵场的过程中应该不会摄食大型游泳动物；而进入鄱阳湖产卵场后会开始摄食日本沼虾和秀丽白虾.这种两阶段的现象可能反映出了刀鲚的一种在洄游通道上节约能量，以利长距离溯河；而在产卵场补充能量，以利于性腺最终成熟的生存策略.;Estuarine tapertail anchovy(Coilia nasus) is a valuable commercial fish in the Yangtze River. It is traditionally believed that C. nasus do not feed during their anadromous migration, but this issue is not yet fully clarified. As a pilot study on feeding of C. nasus during the whole process of anadromous migration, the present study investigated the nekton(e. g. shrimp, fish) in stomach and intestinal contents of C. nasus fish (confirmed as anadromous individuals by otolith microchemical analysis) previously collected in the Yangtze River's estuary, Chongming Island of Shanghai City, sections in Jiangsu and Anhui Provinces, and connected Lake Poyang in Jiangxi Province. The results showed that C. nasus from the river estuary and sections of Jiangsu and Anhui Provinces did not feed nekton and their stomach fullness indices were at 0 degree. In contrast, all C. nasus from Lake Poyang obviously fed nekton and their stomach fullness indices were at 4 to 5 degree. Furthermore, the nektons in stomach contents of the fish were all freshwater shrimps (Macrobrachium nipponense and Exopalaemon modestus), and one and two prawns were found in the stomach contents of 29% and 71% of the C. nasus fish, respectively. However, no nekton residual could be found in the intestinal contents of C. nasus studied. Since the Lake Poyang has been confirmed as a spawning site of anadromous C. nasus, the present study revealed a possible two-step-feeding process for the fish in the Yangtze River, namely, C. nasus may not feed (at least nekton) when moving upstream through the estuary and migratory channel in the sections of Jiangsu and Anhui Provinces, while they may start to feed shrimps of M. nipponense and E. modestus when entering the spawning site in the Lake Poyang. These phenomena may reflect a survival strategy of Yangtze C. nasus, i. e., the fish keeps fasting to save energy for its long distance anadromous movement, but starts to feed to supply energy for full gonad maturation and finish breeding.