Electric Organ Discharge Activity Research Articles

Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil with evidence for a dormancy period

The reproductive biology and feeding habits of the hypopomid Brachyhypopomus bombilla were studied. The species has seasonal behavior, with breeding and feeding activity occurring mostly during the Southern Hemisphere spring and summer. We defined fractional spawning for the species and a relative fecundity similar to those previously reported for other gymnotiform species. According to the analysis of the food items, B. bombilla was included in the trophic category invertivorous, feeding mainly on autochthonous insects. The reproductive periods of males and females as well as female feeding activity were significantly related to the photoperiod. During a period of 5 months, when the lowest water temperatures and shortest photoperiod were recorded, all the specimens of B. bombilla were found buried in the muddy bottom of the creek, with lower electric organ discharge activity, empty stomachs, and gonads in early stages of the maturation process. This period, herein defined as a dormancy period, is reported here for the first time for a species of the Gymnotiformes order.

Responses of electric fish (Family Mormyridae) to chemical changes in water quality: III. Heavy metals

Abstract The effects of varying concentrations of three heavy metals (cadmium, chromium and copper) have been examined using two species of weakly electric fish, Gnathonemus petersi and G. tamandua (Family Mormyridae). Both species are found to be sensitive to the following range of concentrations: cadmium ‐ 100 ‐ 200 μg l‐1, hexavalent and trivalent chromium ‐ 200 ‐ 400 μg l‐1, and copper 5.0 μg l‐1 ‐ 0.1 mg l‐1. Response takes the form of modification of electric organ discharge activity, although the pattern of this response is variable.

Electric Organ Discharge Displays during Social Encounter in the Weakly Electric FishBrienomyrus nigerL. (Mormyridae)

AbstractWe investigated the electric organ discharge (EOD) activity of the mormyrid fishBrienomyrus nigerduring social encounters. The fish were contained in porous ceramic shelters and tested alone and in pairs in an experimental tank designed to restrict communication to the electrosensory modality. We moved one fish toward and away from a stationary conspecific, beginning at a distance known to be outside the range of communication (250 cm). Baseline EOD activity was recorded prior to interaction and categorized as ‘variable’, ‘regular’, and ‘scallop’. When moved closer together, the fish modulated this baseline activity in four ways: (1) At 100–130 cm apart, the stationary fish emitted a maximum of sudden EOD rate increases which defined the outer limit of its communication range. (The associated Electric Field Gradient was 1 μV/cm). (2) Long EOD cessations, which we called social silence, lasted from 5–130 s and occurred most frequently when the fish were 36 to 55 cm apart (EFG: 100 μV/cm). The duration of social silence was negatively correlated (r = − 0.862) with the responding fish's size, and was independent of the partner's sex and size. Fish whose EOD baseline pattern was ‘scallop’ were least likely to fall electrically silent, and those that were categorized as ‘regular’ or ‘variable’ were most likely to cease discharging. (3) Within electrolocation range, fish ‘regularized’ their EOD activity while the partner was ‘silent’ (EFG: 1 mV/cm). (4) Following long EOD cessations the fish resumed discharging with characteristic EOD rebound patterns. The possible ethological significance of these findings is discussed.

Categorisation of Interpulse Intervals and Stochastic Analysis of Discharge Patterns in Resting Weak-Electric Mormyrid Fish (Gnathonemus Petersii)

AbstractInter-individual similarities in the electric organ discharge activity of immobile, isolated and undisturbed mormyrid fish were investigated. Two types of analysis were performed on the discharge patterns of 10 Gnathonemus petersii: (1) The Bout Interval Criterion method was used to categorise the intervals between consecutive electric pulses; (2) an analysis of sequences of acts was performed to study the serial ordering of the interpulse intervals. Interpulse intervals were demonstrated to belong to distinct classes, having similar limits for most animals. Most fish show five classes of interpulse intervals (23 to 68 ms; 69 to 108 ms; 109 to 170 ms; 171 to 212 ms; >212 ms), to which a sixth class (<23 ms) is added in some cases. Each class contains a similar number of intervals in all individuals. Particular associations were found between the occurrences of interpulse intervals belonging to different classes. Some of these associations (for example BB and EC) are displayed by most fish, whereas others express individual differences in the patterns of discharge. The discharge of immobile, undisturbed, isolated mormyrid fish is thus shown to present many similarities among individuals. Inter-individual differences exist only in the serial ordering of the intervals, where they arc best regarded as variations around a same theme. The absence of overlapping between the two main categories of interpulse intervals (category I: 69 to 108 ms; category II: 171 to 212 ms), as well as the constancy of their baselines, suggest that two oscillating systems participate to the electromotor command. The stochastic analysis of the serial ordering of the interpulse intervals suggest in addition that these two oscillators do not function independently. Momentaneous modifications of the activity of these two oscillators would provide an economical explanation for the various changes in the types of interpulse intervals associated with behavioural state or social interactions.

Representation of time-dependent correlation and recurrence time functions. A new method to analyse non-stationary point processes.

Correlation functions based on time averaging are not suited to study non-stationary point processes (e.g. the electric organ discharge activity of weakly-electric pulse fish). To overcome this problem, we present here a time-dependent correlation method, which can also be applied to study complicated correlations of moderately non-stationary point processes (e.g. neuronal spike trains). Indication of recurrence time aspects of the point processes provides a more complete representation of the correlation functions. In addition higher order correlations between two point processes are represented.

Ethological observations on the electric organ discharge behaviour of the electric catfish, Malapterurus electricus (Pisces)

1. Electric organ discharge (EOD) volleys emitted by the electric catfish, Malapterurus electricus, were recorded and sampled for 108 consecutive hours from the fish's natural habitat, a selected study area in the Swashi River, a tributary of the man-made Lake Kainji in Nigeria. 2. M. electricus intermittently generates different types of EOD volleys that start with a high-frequency phase, and range in duration from 2 ms to over 8 s with from 2 to over 600 pulses (EODs). 3. The catfish's EOD activity exhibited a daily activity rhythm which was correlated with local changes in light intensity. The EOD activity remained at a constant level throughout the day from 0700 h to 1800 h. Shortly after sunset, between 1800 h and 1900 h, it increased fivefold to its peak value at 1900 h. The occurrence of EOD volleys declined throughout the night with a noticeable drop to the daytime low after sunrise between 0600 h and 0700 h. During the first 6 h following sunset, the volleys were significantly longer and consisted of more EODs than the daytime volleys. It is inferred that M. electricus feeds most successfully during the early hours of the night. 4. A hitherto unknown type of Malapterurus EOD activity was discovered: during night-time, volleys consisting of more than 16 EODs were occasionally preceded by a low-frequency train of from 1 to 11 EODs. The occurrence rate of these pre-volley EODs was positively correlated with the duration of the ensuing volley (and its number of EODs). The peak pre-volley activity occurred during the first 4 h after sunset, with an average of 38% of all volleys preceded by this type of activity. The adaptive significance of the nocturnal pre-volley EODs as prey detection mechanism is discussed.

Motor programmes and electroreception in mormyrid fish

1. A repertoire of five probing motor acts (PMAs) is used by Marcusenius cyprinoides in the exploratory behaviour of novel objects, introduced into the fish's surroundings: chin probing, ‘va et vient,’ lateral probing, tangential probing, and stationary probing. 2. Four of these PMAs are displayed at a defined distance from the object: 6.8±0.4 cm for a metallic rod and 3.1±0.5 cm for a porous porcelain tube. 3. The exploratory behaviour is accompanied by the appearance of a characteristic electric organ discharge activity mode in the interpulse interval histogram. This pattern is typically emitted during va et vient, but occurs also during other acts of exploratory behaviour. 4. The results indicate that PMAs are probably used to reproducably determine the conductivity characteristics of an object.

Influence of Water Temperature on the Electric Organ Discharge (Eod) of the Weakly Electric Fish Marcusenius Cyprinoides (Mormyridae)

1. The influence of different water temperatures on the electric organ discharge (EOD) of a mormyrid fish Marcusenius cyprinoïdes was studied. The range of the water temperatures was fixed according to the seasonal temperature variations of the rivers in Central Africa, the natural habitat of this species. 2. The EOD activity was characterized using the following parameters: mean EOD rate, EOD pattern in the form of Interpulse Interval Histograms (IIH), IIH range, and shortest pulse interval. These parameters remained constant during control experiments at constant temperature (27 degrees C) for 4 days. 3. The mean EOD rate increases with increasing water temperatures. The lowest mean EOD rate is always found at 17 degrees C, the highest between 26 and 33 degrees C. The characteristics of the IIH are modified by stepwise temperature increases. These IIH show during high temperatures (26-33 degrees C) similar patterns to those previously observed during high level motor activity and excitement. The IIH range diminishes with stepwise temperature increases. The shortest pulse interval has a negative, linear correlation with water temperature. 4. The possible role of water temperature in the reproduction of the mormyrids is discussed. The high discharge rate of M. cyprinoïdes produced by high water temperatures during the rainy season could serve to improve the resolution of the electroreceptors during this period.

Spontaneous discharge rhythms and social signalling in the weakly electric fish Pollimyrus isidori (cuvier et valenciennes) (Mormyridae, Teleostei)

The electric organ discharge (EOD) signalling of isolated and of socially interacting Pollimyrus isidori was analyzed. 1. EOD interval histograms of resting animals showed wide ranges with three modes of 12 to 15 ms, of around 92 ms, and of 220 to 230 ms (Fig. 4a). In number and/or position of modes, the P. isidori histograms were clearly different from those shown by four other mormyrid species: Gnathonemus petersii, Mormyrus rume, Brienomyrus niger, Brienomyrus brachyistius. 2. The EOD interval histograms of swimming P. isidori (Fig. 4a) displayed only one mode of around 50 ms and closely resembled the EOD activity exhibited by G. petersii, B. niger, and B. brachyistius. 3. During overt attack (Figs. 4b, 6, 7a), P. isidori displayed high discharge rates as do G. petersii, B. niger, and M. rume. The EOD time patterns of the displays were clearly distinct from the other species' displays. 4. These data suggest the possibility that mormyrids might recognize conspecifics from their resting- or attack-associated EOD time patterns, not, however, by monitoring EOD swimming activity. During this behavior, species identification would seem possible only by the analysis of spectral cues from the properties of the individual EOD pulses (cf. Fig. 3). Compared with the other species mentioned above, the extremely short EOD of P. isidori contains much more energy in a high frequency band (peak: 10 kHz with energy beyond 30 kHz). 5. Different individuals of P. isidori displayed either a Preferred Latency Response of approx. 12 to 14 ms or a response consisting in avoiding a 10 to 20 ms discharge latency to foreign electrical stimuli (Figs. 8–10). While the avoidance response may be considered a jamming avoidance behaviour, reducing the probability of coincidences with a conspecific's EODs, the Prefered Latency Response in P. isidori would have the opposite effect and ‘jam’ a conspecific's signals when the latter displays high discharge rates occurring during attack behaviour. Whether these alternative types of latency behaviour are sex, age, or rank correlated remains to be investigated.

Electric organ discharge activity of resting and stimulated Gnathonemus petersii (Mormyridae).

1. The electric organ discharge (EOD) activity of 12 isolated Gnathonemus petersii was analyzed by means of interpulse interval histograms (IIH), joint interval histograms (JIIH) as well as by measurements of the instanaeous frequency of consecutive intervals. 2. The IIH of 10 resting fish was characterized by three modes and in two fish by two modes. The higher frequency mode (25-62 Hz) corresponds to burst-like frequency increases (BA) of the EOD, the lower are due to inter-burst activity (IBA). 3. Frequency ranges of modes are remarkably constant during following days and even months. Because of the individual specific position of modes, the IIH renders it possible to distinguish individuals from one another. 4. JIIH computation of the EOD of resting G. petersii reveals that besides a random activity, two types of correlation exist between consecutive intervals (regularization). The first, type I regularization, is characterized by consecutive intervals of nearly equal duration. It occurs in the BA of trimodal and bimodal fish, and also in the IBA range of bimodal fish. The second, type 2 regularization, is characterized by alternating long and short intervals, corresponding to the second and third mode, which are displayed during the IBA of trimodal fish. 5. The transition from IBA to BA and vice versa is brief and distinct. The analyses of long periods of activity reveal that the resting G. petersii displays its entire activity spectrum (BA and IBA) in a sequence of about 200 intervals. 6. When stimulated by the discharges of a conspecific or another mormyrid, the EOD activity of G. petersii becomes more regular. Trains of up to 330 equal intervals (type I regularization) were observed. The preferred frequency range for this emission is individual specific and is situated in the minimum between BA and IBA. Its appearence is also characteristic for mechanically stimulated G. petersii. 7. The results described here give evidence that G. petersii emits at least at 6 preferred ranges of frequency.