Influence of environmental factors and individual traits on the diet of non-native hybrid bigheaded carp (Hypophthalmichthys molitrix × H. nobilis) in Lake Balaton,Hungary

Planktivorous silver carp and bighead carp (collectively, the bigheaded carps) have been stocked worldwide and their invasion has caused severe impacts on many freshwater ecosystems. Exploiting the chance provided by the specific hybrid bigheaded carp stock in Lake Balaton (Hungary) covering the entire morphological range between the two species (including gill raker morphology), we implemented a comprehensive study (1) to reveal the feeding habits of hybrid bigheaded carps living in a mesotrophic, lacustrine habitat and (2) to assess how biotic and abiotic environmental factors and gill raker morphology affect diet composition. We found that all bigheaded carps utilized primarily zooplankton and neglected the scarce and inefficiently digestible phytoplankton, irrespective of gill raker morphology. Moreover, we observed strikingly high levels of inorganic debris consumption, but the proportion of inorganic matter in the guts was not associated directly with the concentration of suspended inorganic particles. Variance in the diet composition of bigheaded carps was related mostly to environmental factors, including the wind-induced resuspension of inorganic particles and seasonally variable availability of food resources. In conclusion, the effects of abiotic environmental factors and available food resources could overwhelm the effect of gill raker morphology in shaping the feeding habits of bigheaded carps.

     

The 5-HT immunoreactive innervation of the Helix procerebrum

In the procerebrum of terrestrial snails, 5-HT is a key modulatory substance of the generation of synchronous oscillatory activity and odor learning capability. In this study, we have analyzed the characteristics of the 5-HT-immunoreactive (5-HT-IR) innervation of the distinct anatomical regions of the procerebrum of Helix pomatia, applying correlative light- and electron microscopic immunocytochemistry. A dense network of 5-HT-IR innervation was demonstrated in the cell body layer, meanwhile a varicose fiber system of different density occurred in the different neuropil regions. At the ultrastructural level, labeled varicosities were found to contact both procerebral cell bodies, and different unlabeled axon profiles in the neuropils. The labeled structures established mostly close non-specialized membrane contacts with the postsynaptic profiles. The overall dense distribution of 5-HT-IR innervation supports a general modulatory role of 5-HT in processing different olfactory events.     

Potassium channels in the Helix central nervous system: preliminary immunohistochemical studies. Short communication

Distribution of the potassium channel of Kv4.3 type was investigated in the central nervous system (CNS) of Helix pomatia by immunohistochemistry. Immunopositive neurons were found widely distributed in the CNS, present mostly in smaller groups in the different central ganglia but not in the visceral ganglion. Labeled fibers were characteristic for not only the neuropils of all ganglia but also the connective tissue sheath around the CNS and the aorta wall were richly innervated. Western blot analysis revealed a clear identity with the mammalian Kv4.3 subunit, suggesting an evolutionary conserved structure of this channel type. Our preliminary results provide a steady basis for further experiments aiming partly at the identification of other potassium channel types and partly the ultrastructural localization of Kv4.3.