ABSTRACT
Weak electric discharges generated by the two species of the African upside-down catfishes, Synodontis sorex and S. batensoda are described. In both species two types of discharges were recorded in the course of aggressive-defense interactions in the pairs of individuals: short simple biphasic and longer (duration >20 ms) discharges with more complex waveform. The discharges of the latter type seem to result from a temporal summation (with various latency) of simple discharges. It is suggested that formation of the long quasimonopolar discharges enhances the coincidence of frequency spectrum of the catfish discharges with maximum sensitivity range of their ampullary electroreceptors.
Subject(s)
Catfishes/physiology , Electric Organ/physiology , Action Potentials , AnimalsABSTRACT
The waveform and some characteristics of the electric organ discharges have been studied in 11 individuals of Cyphomyrus petherici, the only representative of the genus in the Nilotic fauna. The discharge is characterized by three to five phases with a prevalence of the second phase in terms of the relative amplitude and a wide variability of the total duration of discharge (from 212 to 558 µs). The comparison of the discharges of the species under study with those in the congeneric species and representatives of the genus Pollimyrus (which previously encompassed C. petherici) demonstrates a general similarity of the C. petherici discharges with those of Cyphomyrus, but not Pollimyrus. This is in agreement with the correspondence of the discharge characteristics observed in other mormyrids to the phylogenetic position and taxonomic status of the species.
Subject(s)
Electric Fish/physiology , Electric Organ/physiology , Animals , RiversABSTRACT
The paper reports spontaneous generation of weak electric discharges with an amplitude of 0.4-1.0 mV and a frequency of 3-9 min-1 by solitary Synodontis caudovittatus fish. When fish individuals were tested in pairs, their aggressive-defense interactions were associated with an increase in the amplitude of the discharges (up to 30-45 mV) compared to the discharges of individual fish, while the duration of the pulses increased up to 20-25 ms due to the prolongation of the second phase. In S. eupterus, electric activity was recorded only in the course of aggression-defense interactions, while spontaneous generation of discharges was not observed at all. The paper discusses the different aspects of electrocummunication between the catfish including the role of the reversion of polarity of the merged summated discharges with increased duration.
Subject(s)
Catfishes/physiology , Electromagnetic Phenomena , Animals , Electric Fish/physiology , Electric Organ/physiologyABSTRACT
The heavy metal contents in the scales of bream (Abramis brama) from the Mozhaisk Reservoir collected in the second half of the 1980s were compared to the current values. The concentrations of three out of the seven elements studied in the bream scales have changed severalfold during the past quarter century: that of strontium has decreased, and those of barium and lead have increased. Short-term variations of heavy metal contents have proved to be smaller than the observed long-term differences. There is grounds to believe that these long-term differences adequately reflect the changes that have occurred in the water body.
