. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. BEHAVIOR OF WEAKLY ELECTRIC FISHES 205 times extending forward to a point anterior to the visceral cavity (Bennett, 1961, 1968). Fish in group 2 had auxiliary organs also of muscular origin in the head (Bennett, 1962). Localisation of electrical activity Table II summarizes the intensities of electrical activity recorded with fish detector at various locations underwater in or near the main river. No activity was ever detected within the flooded (igapo) forest along the right bank. Low frequency activity was detected within
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. BEHAVIOR OF WEAKLY ELECTRIC FISHES 205 times extending forward to a point anterior to the visceral cavity (Bennett, 1961, 1968). Fish in group 2 had auxiliary organs also of muscular origin in the head (Bennett, 1962). Localisation of electrical activity Table II summarizes the intensities of electrical activity recorded with fish detector at various locations underwater in or near the main river. No activity was ever detected within the flooded (igapo) forest along the right bank. Low frequency activity was detected within the igapo forest along the left bank. Only low frequency activity was detected in small streams and inlets and single specimens of Hypopomus sp. and Steatogenys sp. were captured there. Much of the day- time activity detected in deep water, and also along the submerged lines of trees. FIGURE 2. Characteristic waveforms of discharge for groups of fishes (Table I). Record- ings were made with a monopolar electrode placed near the head; a head positive deflection is upwards. A time calibration bar indicates 2 msec (1 msec for waveform 2) ; the maximum signal detected was about 50 mV. at night, was high frequency (Table I, column 8, 9). On a basis of frequencies and waveforms of activity, 6 groups of fishes were identifiable, corresponding to the six groups of electrically distinct fishes studied in aquaria (Table I, column 7). Table II indicates that locations where activity was highest during the day became silent at night, and vice-versa. Activity during the day in deep water ap- peared to be concentrated in patches, although always at or near the bottom. At night, activity was spread continuously along the tree line, from about 1 m to the bottom (Table III). Particularly intense patches of daytime activity were found just inshore from the ship anchorage (Fig. 3). A rocky area extending underwater from the shore probably provided secure resting places for the fishes. Transects o
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
