大鳍鱊对4种沉水植物的选择性摄食

杂食性鱼类往往是修复后浅水湖泊的优势鱼类。大鳍鱊是一种小型杂食性鱼类，在无锡蠡湖生态修复区内发展成为优势种；虽主要以沉水植物为食，但对不同沉水植物的选择性目前尚不清楚.目前有关杂食性鱼类对沉水植物影响的研究多集中在个体较大的种类（如鲤、鲫），而对小型杂食性鱼类的研究较少。本文通过受控实验,研究了大鳍鱊对4种沉水植物（轮叶黑藻Hydrilla verticillata、密刺苦草Vallisneria denseserrulata、金鱼藻Ceratophyllum demersum和穗花狐尾藻Myriophyllum spicatum）的选择性摄食，分析了大鳍鱊对这些沉水植物生长的影响。结果显示:1)大鳍鱊组的水体营养盐浓度显著高于对照组，而pH值则显著低于对照组；2)肠道内含物分析结果显示：穗花狐尾藻和金鱼藻是大鳍鱊的主要食物，其所占肠道内含物的体积比分别为75%和17%；而大鳍鱊对密刺苦草的选择性较低(8%)，且内含物中未出现黑藻；3)大鳍鱊显著抑制了穗花狐尾藻和金鱼藻的生长(RGR),而对轮叶黑藻和密刺苦草的RGR有促进作用。沉水植物在维持湖泊生态系统结构稳定与湖泊生态修复中发挥重要作用，大鳍鱊等小型鱼类与沉水植物关系密切，主要生活在沉水植物丰富的水域。我们的研究结果发现大鳍鱊可显著增加水体营养盐浓度，对不同沉水植物有明显的摄食选择性，其摄食活动可显著降低沉水植物的生物量。因此，大鳍鱊或者其它小型杂食性鱼类(如麦穗鱼和鲹等)可能会通过选择性摄食沉水植物的途径影响沉水植物群落结构和生物量，严重时可能会对湖泊生态系统结构的稳定性产生负面影响。所以,在湖泊管理与生态修复中,需要关注此类小型杂食性鱼类的种群规模，将其控制在较低生物量水平。该研究探讨了大鳍鱊的选择性摄食行为以及该行为带来的影响，为浅水湖泊的修复提供了参考。

Feeding Preferences of Acheilognathus macropterus on Four Submerged Macrophytes

Omnivorous fish dominate the fish assemblages in restored lakes. A small omnivorous bitterling fish (Acheilognathus macropterus) develops to be the dominant species in the restored Lake Wuli, China, and submerged macrophytes constitute a large proportion of the fish diet. However, the feeding preferences of bitterling on submerged macrophytes are, so far, not elucidated. Studies on the effects of omnivores on submerged macrophytes are mostly on large-sized species (e.g., Cyprinus carpio and Carassius carassius), while neglecting the effects of small-sized species. We conducted a mesocosm experiment to study the feeding selectivity of bitterling on four submerged macrophytes (Vallisneria denseserrulata, Hydrilla verticillata, Ceratophyllum demersum and Myriophyllum spicatum) and the growth of each species. Our result showed that the nutrient concentrations in the fish treatment were significantly than the controls, while bitterling substantially reduced the pH values compared with the control treatment. The bitterling gut contents analysis results showed that bitterling preferred M. spicatum and C. demersum, and their proportion in the guts were 75% and 17%, respectively; however, bitterling fed less on V. denseserrulata (8%) but no H. verticillata were found in the fish guts. At the end of the experiment, the relative growth rates (RGR) of both M. spicatum and C. demersum were significantly reduced by the bitterling fish, the RGR of H. verticillata and V. denseserrulata were enhanced by the fish but did not differ significantly with that of the controls. Furthermore, bitterling significantly reduced the total biomass of the four macrophytes compared with the control treatment. Submerged macrophytes play a key role in structuring the lake ecosystems, and are popularly used in restoration of the eutrophic shallow lakes. The omnivore bitterling and other small fishes are highly correlated with submerged macorphytes. However, our findings showed that bitterling could selectively feeding on submerged macrophytes, significantly suppressed the RGR of its largely grazed species (e.g., M. spicatum and C. demserum). Therefore, bitterling and may also other small omnivores (e.g., Pseudorasbora parva and Hemiculter leucisculus) may change the community structure and reduce the biomass of submerged macrophtyes via selective grazing, thus negatively affect the water quality and stability of lake ecosystems. Thus, in the management and restoration of shallow lakes, we should pay more attention on the population development of these small omnivorous fishes, and manners should be taken to keep the small omnivores in low biomass when they became abundant.