鲢对藻类摄食效应的室内模拟研究

THE PREDATOR EFFECTS OF SLIVER CARP ON DIFFERENT ALGAL SPECIES INSIDE AQUARIUM

  • 摘要: 为研究鲢(Hypophthalmichthys molitrix)对藻类的摄食作用, 采用小环藻(Cyclotella)、小球藻(Chlorella)、微囊藻(Microcystis)和东湖原水开展了小规格鱼种的养殖试验, 对鲢摄食和排泄物进行了研究。结果显示: 在3 种纯培养藻种投喂下鲢存活率从高到低依次是小环藻组 小球藻组 微囊藻组;相应地, 鲢对藻的平均摄食率排序也是小环藻组 小球藻组 微囊藻组。在显微镜下观察粪便发现大部分小环藻为空壳, 一部分小球藻外部形态结构不完整, 外部形态完整的小球藻则色泽暗淡、内部结构紊乱, 微囊藻没有明显变化;3 种藻类细胞的受损率分别为20.04%、7.13%和1.97%。叶绿素荧光活性显示, 粪便中小环藻基本失去光合活性, 小球藻活性极显著降低(P0.01), 微囊藻活性明显降低(P0.05), 东湖原水处理组光合活性较对照极显著降低(P0.01)。对东湖水饲喂试验组排泄物的检测发现, 浮鞘丝藻Planktolyngya、鱼腥藻Anabeana(有破损)、假鱼腥藻Pseudoanabaena 和颤藻Oscillatoria 细胞受损严重;空星藻Coelastrum 和盘星藻Pediastrum 细胞部分破损;针杆藻Synedra、小环藻、桥弯藻Cymbella 和舟形藻Navicula 多为空壳。鱼粪中平裂藻Merismopedia、微囊藻、浮鞘丝藻、鱼腥藻、颤藻、卵囊藻Oocystis、栅藻Scenedesmus 和衣藻Chlamydomonas 在重新培养后恢复了生长。本研究显示硅藻尤其是小环藻、针杆藻和舟形藻对鲢摄食最敏感;栅藻、卵囊藻和平裂藻对摄食压力不敏感。研究表明鲢捕食对藻类群落结构有明显的改变效应, 利用鲢的滤食进行藻类群落调节和水华防控具有可行性。

     

    Abstract: To study the ingestion and digestion of different algal species by sliver carp, we conducted feeding and feces experiments in aquarium microcosms. Sliver carps were fed with three species of algae (Cyclotella, Chlorella and Microcystis aeruginosa), and the ingestion rates per fish weight for the three species were 2.70104, 1.99104 and 1.06104 cells/(gh) respectively. In feces, the ratios of the complete cells to the imperfect cells were 20.04%, 7.13% and 1.97% for the three species respectively. Microcosm experiments were conducted in aquariums filled with water from the Donghu Lake for two weeks. Each aquarium had 20 fish total weight (4.50.021) g inside, and there were three replicates in one experiment. We found that after 20 days the cell density in the aquariums was significantly reduced compared to the control. Planktolyngbya accounted for 87% of the phytoplankton density in feces, and Merismopedia sp., Pseudoanabaena sp., Oscillatoriaceae sp. and Microcystis sp. accounted for 11%, but Raphidiopsis sp., Scenedesmus spp., Coelastrum sp. only formed a very small portion. The morphology of Oscillatoria sp., Spirulina sp., and Pediastrum sp. appeared to be incomplete, while Synedra sp., Navicula sp. and Cyclotella sp. had a nearly vacant-shell shape. We collected the feces to feed the hungry sliver carps and did not observe any Pediastrum sp., Cyclotella sp. or Synedra sp. in the new discharge. However, we still found Planktolyngbya sp., Anabeana sp., Pseudoanabaena sp., Merismopedia sp., Microcystis sp., Raphidiopsis sp., Oscillatoriaceae sp., Microcystis sp., Scenedesmus spp., Oocystis sp., Pandorina morum sp., Coelastrum sp., Chlamydomonas sp. and Cymbella sp. After a 10d culture of the feces in the medium, we observed the revival of Planktolyngbya sp., Oscillatoriaceae sp., Merismopedia sp., Anabeana sp., Pseudoanabaena sp., Microcystis sp., Scenedesmus spp., Chlamydomonas sp. and Oocystis sp. The level of chlorophyll a decreased slightly at first and then increased in fish groups. Our study suggested that sliver carp could filter phytoplankton with the size of 250 m, and that sliver carp might mainly feed on diatoms, of which the ingestion and digestion was easier than that of green algae and blue-green algae. The results also indicated that Cyclotella sp. and Navicula sp. were sensitive to the predator stress. Therefore silver carp could be an efficient tool to regulate the algal population and the phytoplankton communities.

     

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