In common with many other suspension feeders, the freshwater mussel Dreissena polymorpha has a maximum filtration rate at low food concentrations and a maximum ingestion rate at high food concentrations. These high rates, which reflect the potential maximum food uptake of the animal, are called the filtration capacity and the ingestion capacity respectively. The ingestion capacity was attained without forming pseudofaeces with Chlamydomonas reinhardii as food. The incipient limiting level could be calculated as the quotient of these two values. A decrease of the filtration rate at high food concentrations was correlated with changes in pumping activity, which showed more frequent interruptions, or a lower level of water transport. Dreissena can filter out particles of diameter greater than 0.7 μm from the water. Retention reaches a plateau at about 5 μm particle diameter. Scanning electron micrographs of the arrangement of the cilia on the gill filaments are given.
Feral populations of tropical fish species in temperate climates like Central Europe are a rare but repeatedly observed phenomenon. Due to the influence of industrial or geothermal heated water, released tropical fish may be able to survive harsh winter conditions. Here we characterize a newly discovered thermally polluted river, with an established population of the guppy (Poecilia reticulata) co-occurring with native species. Through a mark-recapture approach, we estimated the population size of the guppies close to the warm water inflow to be around 2000 individuals during summer and we further provide descriptive demographics of this population which allow us to assume it is well established in that river. Further, we found some of the sampled specimen being parasitized by Camallanus roundworms, thus showing the guppies' host potential for this genus of internal parasites. The popularity and widespread distribution of guppies as ornamental fish often leads to their intentional or unintentional release into the wild where they are often pioneer species in anthropogenically heavily modified habitats. Guppies threaten native species through niche competition and transmission of diseases. Accordingly, early awareness and knowledge on the status of non-native populations is crucial for effective management strategies.
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