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In humans and other vertebrates, sensory information is sometimes lateralized towards one brain hemisphere that dominates the control of a task. Although sensory lateralization may depend on the stimuli being processed, the degree or direction of lateralization can differ according to behavioural phenotype. Accordingly, personality may play an important role in lateralization, yet there is a lack of evidence regarding how lateralizations are utilized to process information and promote a personality-based response to a particular situation. Here we show that simultaneous stimulus processing and organization of personality-based responses can be accomplished via differences in laterality between senses. We demonstrate this by examining novel object inspection in the weakly electric fish Gnathonemus petersii . We found that electrosensing is lateralized in this species, but differently between personality phenotypes: bold fish were lateralized towards the right hemisphere and timid fish the left. By contrast, visual laterality did not vary with personality; rather the left hemisphere was dominant across the population, as is common for fish when visually analysing unfamiliar objects. This evidence reveals differences in functional laterality between sensory systems and the role of personality in eliciting these differences. The species has a stronger input of electrical signals than visual signals in its brain; therefore, sensory representation in the brain might drive the laterality differences. [ABSTRACT FROM AUTHOR]

Mormyrid fish rely on reafferent input for active electrolocation. Their electrosensory input consists of phase and amplitude information. These are encoded by differently tuned receptor cells within the Mormyromasts, A- and B-cells, respectively, which are distributed over the animal’s body. These convey their information to two topographically ordered medullary zones in the electrosensory lateral line lobe (ELL). The so-called medial zone receives only amplitude information, while the dorsolateral zone receives amplitude and phase information. Using both sources of information, Mormyrid fish can disambiguate electrical impedances. Where and how this disambiguation takes place is presently unclear. We here investigate phase-sensitivity downstream from the electroreceptors. We provide first evidence of phase-sensitivity in the medial zone of ELL. In this zone I-cells consistently decreased their rate to positive phase-shifts (6 of 20 cells) and increased their rate to negative shifts (11/20), while E-cells of the medial zone (3/9) responded oppositely to I-cells. In the dorsolateral zone the responses of E- and I-cells were opposite to those found in the medial zone. Tracer injections revealed interzonal projections that interconnect the dorsolateral and medial zones in a somatotopic manner. In summary, we show that phase information is processed differently in the dorsolateral and the medial zones. This is the first evidence for a mechanism that enhances the contrast between two parallel sensory channels in Mormyrid fish. This could be beneficial for impedance discrimination that ultimately must rely on a subtractive merging of these two sensory streams. [ABSTRACT FROM AUTHOR]

Most animals possess multiple sensory systems, which can be used during navigation. Different senses obtain environmental information on different spatial scales and thus provide a different basis for efficient navigation. Here we used the weakly electric fish Gnathonemus petersii to investigate how different sensory inputs influence the navigational strategy and whether landmark information can be transferred flexibly between two sensory systems. Fish were trained to swim through a maze using a certain route indicated by either visual landmarks, electrical landmarks or without any landmarks. In subsequent tests, egocentric (internal cues, such as motion patterns) and allocentric cues (external cues like landmarks) were put in conflict by relocating the local landmarks. We found that all fish, independent of the available sensory input, chose the egocentric over the allocentric route. However, visual landmarks significantly improved the training duration compared to the other groups, suggesting an involvement of allocentric visual cues during route acquisition. In a second experimental series, fish were trained to use either visual or electrical landmarks for navigation and were subsequently tested in sensory transfer tests. Fish trained with visual landmarks were able to learn this allocentric navigation task and were capable of cross-modal landmark recognition, although navigation based on electrical landmarks was less efficient. The fish trained with electrical landmarks did not learn the task at all, suggesting that the short perceptual range of the electric sense prevented learning of allocentric navigation. Together our results show that the type of sensory input influences the efficiency of allocentric navigation in G. petersii and that these fish can use egocentric and allocentric strategies flexibly to navigate successfully under varying environmental conditions. [ABSTRACT FROM AUTHOR]

During active electrolocation, the weakly electric fish Gnathonemus petersii judges the distance and impedance of nearby objects. Capacitive objects, which modulate local amplitude and waveform of the fish's electric probing signals, cast amplitude and waveform images onto the fish's electroreceptive skin. For an unambiguous estimation of the impedance and distance of an object, the animal has to deal with multiple dependencies of object and image parameters. Based on experimentally recorded amplitude and waveform images, we investigated possible strategies of the fish to unequivocally determine both the distance and the impedance of capacitive objects. We show that the relative slope in amplitude images, but not in waveform images, is independent of object impedance and is a measure of object distance. Distance-invariant impedance estimators were obtained by two different analytical strategies. The peak modulations of both image types were 'calibrated' with the relative slope of the amplitude image. Impedance estimators were obtained whenever these pairs of image features (peak and relative slope) were related dynamically over two consecutive distances. A static impedance estimator termed 'electric colour' is postulated to arise from the relationship of an amplitude and waveform image. Our results confirm that electric colour is indeed unaffected by object distance. For electric colour estimation we suggest a minimalistic approach of just relating the peak modulations of both image types to the basal amplitude and waveform condition. Our results are discussed with regard to the anatomical and physiological organization of the fish's electrosensory neuronal pathways and behavioural strategies of electrolocating fish. [ABSTRACT FROM AUTHOR]

The sensory input that an animal receives is directly linked to its motor activity. Behavior thus enables animals to influence their sensory input, a concept referred to as active sensing. How such behavior can serve as a scaffold for generating sensory information is of general scientific interest. In this article, we investigate how behavior can shape sensory information by using some unique features of the sensorimotor system of the weakly electric fish. Based on quantitative behavioral characterizations and computational reconstruction of sensory input, we show how electrosensory flow is actively created during highly patterned, spontaneous behavior in Gnathonemus petersii. The spatiotemporal structure of the sensory input provides information for the computation of a novel distance cue, which allows for a continuous estimation of distance. This has significant advantages over previously known nondynamic distance estimators as determined from electric image blur. Our investigation of the sensorimotor interactions in pulsatile electrolocation shows, for the first time, that the electrosensory flow contains behaviorally relevant information accessible only through active behavior. As patterned sensory behaviors are a shared feature of (active) sensory systems, our results have general implications for the understanding of (active) sensing, with the proposed sensory flow-based measure being potentially pertinent to a broad range of sensory modalities. [ABSTRACT FROM AUTHOR]

The Electrosensory Lateral Line lobe (ELL) is the first central target where the electrosensory information encoded in the spatiotemporal pattern electroreceptor afferent discharges is processed. These afferents encode the minute amplitude changes of the basal electric field through both a change in latency and discharge rate. In the ELL the time and rate-coded input pattern of the sensory periphery goes through the granular cell layer before reaching the main efferent cells of the network: large fusiform (LF) and large ganglion (LG) cells. The evidence until now shows that granular cells are inhibitory. Given that large fusiform cells are excited by the sensory input, it remains a mystery how the afferent input produce excitation through a layer composed by only inhibitory cells. We addressed this problem by modeling how the known circuitry of the ELL could produce excitation in LF cells with only inhibitory granular cells. Alternatively we show that a network composed of a mix of excitatory and inhibitory granular cell not only performs better, as expected, carrying excitation to LF cells but it does so robustly and at higher sensitivity by enhancing the contrast of the electric image between the periphery and the ELLs output. We then show with refined histological methods that a subpopulation of the granular cells indeed are excitatory, providing the necessary input for this contrast enhancing mechanism. [ABSTRACT FROM AUTHOR]

African weakly electric mormyrid fish show a high diversity of their electric organ discharge (EOD) both across and within genera. Thanks to a recently developed technique of artificial reproduction in mormyrid fish, we were able to perform hybridizations between different genera and within one genus ( Campylomormyrus ). The hybrids of intergenus hybridizations exhibited different degrees of reduced survival related to the phylogenetic distance of the parent species: hybrids of the crosses between C. rhynchophorus and its sister genus Gnathonemus survived and developed normally. Hybrids between C. rhynchophorus and a Mormyrus species (a more basal clade compared to Campylomormyrus s) survived up to 42 days and developed many malformations, e.g., at the level of the unpaired fins. Hybrids between C. numenius and Hippopotamyrus pictus (a derived clade, only distantly related to Campylomormyrus ) only survived for two days during embryological development. Eight different hybrid combinations among five Campylomormyrus species ( C. tamandua , C. compressirostris , C. tshokwe , C. rhynchophorus , C. numenius ) were performed. The aim of the hybridizations was to combine species with (1) either caudal or rostral position of the main stalk innervating the electrocytes in the electric organ and (2) short, median or long duration of their EOD. The hybrids, though they are still juveniles, show very interesting features concerning electrocyte geometry as well as EOD form and duration: the caudal position of the stalk is prevailing over the rostral position, and the penetration of the stalk is dominant over the non-penetrating feature (in the Campylomormyrus hybrids); in the hybrid between C. rhynchophorus and Gnathonemus petersii it is the opposite. When crossing species with long and short EODs, it is always the long duration EOD that is expressed in the hybrids. The F1-Hybrids of the cross C. tamandua × C. compressirostris are fertile: viable F2-fish could be obtained with artificial reproduction. [ABSTRACT FROM AUTHOR]

Most animals use multiple sensory modalities to obtain information about objects in their environment. There is a clear adaptive advantage to being able to recognize objects cross-modally and spontaneously (without prior training with the sense being tested) as this increases the flexibility of a multisensory system, allowing an animal to perceive its world more accurately and react to environmental changes more rapidly. So far, spontaneous cross-modal object recognition has only been shown in a fewmammalian species, raising the question as to whether such a high-level function may be associated with complex mammalian brain structures, and therefore absent in animals lacking a cerebral cortex. Here we use an objectdiscrimination paradigm based on operant conditioning to show, for the first time to our knowledge, that a nonmammalian vertebrate, the weakly electric fish Gnathonemus petersii, is capable of performing spontaneous cross-modal object recognition and that the sensory inputs are weighted dynamically during this task. We found that fish trained to discriminate between two objects with either vision or the active electric sense, were subsequently able to accomplish the task using only the untrained sense. Furthermore we show that crossmodal object recognition is influenced by a dynamic weighting of the sensory inputs. The fish weight object-related sensory inputs according to their reliability, to minimize uncertainty and to enable an optimal integration of the senses. Our results show that spontaneous cross-modal object recognition and dynamic weighting of sensory inputs are present in a nonmammalian vertebrate. [ABSTRACT FROM AUTHOR]

Motor patterns displayed during active electrosensory acquisition of information seem to be an essential part of a sensory strategy by which weakly electric fish actively generate and shape sensory flow. These active sensing strategies are expected to adaptively optimize ongoing behavior with respect to either motor efficiency or sensory information gained. The tight link between the motor domain and sensory perception in active electrolocation make weakly electric fish like Gnathonemus petersii an ideal system for studying sensory-motor interactions in the form of active sensing strategies. Analyzing the movements and electric signals of solitary fish during unrestrained exploration of objects in the dark, we here present the first formal quantification of motor patterns used by fish during electrolocation. Based on a cluster analysis of the kinematic values we categorized the basic units of motion. These were then analyzed for their associative grouping to identify and extract short coherent chains of behavior. This enabled the description of sensory behavior on different levels of complexity: from single movements, over short behaviors to more complex behavioral sequences during which the kinematics alter between different behaviors. We present detailed data for three classified patterns and provide evidence that these can be considered as motor components of active sensing strategies. In accordance with the idea of active sensing strategies, we found categorical motor patterns to be modified by the sensory context. In addition these motor patterns were linked with changes in the temporal sampling in form of differing electric organ discharge frequencies and differing spatial distributions. The ability to detect such strategies quantitatively will allow future research to investigate the impact of such behaviors on sensing. [ABSTRACT FROM AUTHOR]

Goal-directed behavior in most cases is composed of a sequential order of elementary motor patterns shaped by sensorimotor contingencies. The sensory information acquired thus is structured in both space and time. Here we review the role of motion during the generation of sensory flow focusing on how animals actively shape information by behavioral strategies. We use the well-studied examples of vision in insects and echolocation in bats to describe commonalities of sensory-related behavioral strategies across sensory systems, and evaluate what is currently known about comparable active sensing strategies in electroreception of electric fish. In this sensory system the sensors are dispersed across the animal's body and the carrier source emitting energy used for sensing, the electric organ, is moved while the animal moves. Thus ego-motions strongly influence sensory dynamics. We present, for the first time, data of electric flow during natural probing behavior in Gnathonemus petersii (Mormyridae), which provide evidence for this influence. These data reveal a complex interdependency between the physical input to the receptors and the animal's movements, posture and objects in its environment. Although research on spaUotemporal dynamics in electrolocation is still in its infancy, the emerging field of dynamical sensory systems analysis in electric fish is a promising approach to the study of the link between movement and acquisition of sensory information. [ABSTRACT FROM AUTHOR]

Abstract: The weakly electric fish Gnathonemus petersii uses active electrolocation to detect and discriminate between objects in its environment. Objects are recognised by analysing the electric images, which they project onto the fish’s skin. In this study, we determined whether different types of large backgrounds interfere with the fishes’ ability to discriminate between objects. Fish were trained in a food-rewarded two-alternative forced-choice procedure to discriminate between two objects. In subsequent tests, structured and non-structured as well as stationary and moving backgrounds were positioned behind the objects and discrimination performance between objects was measured at different object distances. To define the electrosensory stimuli during the tests, the electric images of the objects and backgrounds used were measured. Without a background G. petersii was able to discriminate between objects up to distances of about 3–4cm. Even though the electric images of background and object superimposed in a complex way, the addition of stationary structured or plain backgrounds had only minor effects on the range of object discrimination. However, two types of moving backgrounds improved electrolocation by extending the range of object discrimination up to a distance of almost 5cm. This suggests that movements in the environment plays an important role for object identification and improves figure–ground separation during active electrolocation. [Copyright &y& Elsevier]

Abstract: Weakly electric fish orient, hunt and communicate by emitting electrical pulses, enabling them to discriminate objects, conspecifics and prey. In addition to the electrosensory modality - although dominating in importance in these fishes - other modalities, like vision, play important roles for survival. The visual system of Gnathonemus petersii, a member of the family mormyridae living in West African blackwater streams shows remarkable specializations: Cone photoreceptors are grouped in bundles within a light reflecting tapetum lucidum, while the rods are also bundled but located at the back within a light-scattering guanine layer. Such an organization does not improve light sensitivity nor does it provide high spatial resolution. Thus, the function of the grouped retinal arrangement for the visual performance of the fish remains unclear. Here we investigated the contrast sensitivity of the temporal transfer properties of the visual system of Gnathonemus. To do so, we analyzed visual evoked potentials in the optic tectum and tested the critical flicker fusion frequency in a behavioral paradigm. Results obtained in Gnathonemus are compared to results obtained with goldfish (Carassius auratus), revealing differences in the filter characteristics of their visual systems: While goldfish responds best to low frequencies, Gnathonemus responds best at higher frequencies. The visual system of goldfish shows characteristics of a low-pass filter while the visual system of Gnathonemus has characteristics of a band-pass filter. Furthermore we show that the visual system of Gnathonemus is more robust towards contrast reduction as compared to the goldfish. The grouped retina might enable Gnathonemus to see large, fast moving objects even under low contrast conditions. Due to the fact that the electric sense is a modality of limited range, it is tempting to speculate that the retinal specialization of Gnathonemus petersii might be advantageous for predator avoidance even when brightness differences are small. [Copyright &y& Elsevier]

In a food-rewarded two-alternative forced-choice procedure, it was determined how well the weakly electric elephantnose fish Gnathonemus petersii can sense gaps between two objects, some of which were placed in front of complex backgrounds. The results show that at close distances, G. petersii is able to detect gaps between two small metal cubes (2 cm × 2 cm × 2 cm) down to a width of c. 1·5 mm. When larger objects (3 cm × 3 cm × 3 cm) were used, gaps with a width of 2-3 mm could still be detected. Discrimination performance was better ( c. 1 mm gap size) when the objects were placed in front of a moving background consisting of plastic stripes or plant leaves, indicating that movement in the environment plays an important role for object identification. In addition, the smallest gap size that could be detected at increasing distances was determined. A linear relationship between object distance and gap size existed. Minimal detectable gap sizes increased from c. 1·5 mm at a distance of 1 cm, to 20 mm at a distance of 7 cm. Measurements and simulations of the electric stimuli occurring during gap detection revealed that the electric images of two close objects influence each other and superimpose. A large gap of 20 mm between two objects induced two clearly separated peaks in the electric image, while a 2 mm gap caused just a slight indentation in the image. Therefore, the fusion of electric images limits spatial resolution during active electrolocation. Relative movements either between the fish and the objects or between object and background might improve spatial resolution by accentuating the fine details of the electric images. [ABSTRACT FROM AUTHOR]

Despite their diversity, vertebrate retinae are specialized to maximize either photon catch or visual acuity. Here, we describe a functional type that is optimized for neither purpose. In the retina of the elephantnose fish (Gnathonemus petersii), cone photoreceptors are grouped together within reflecting, photonic crystal--lined cups acting as macroreceptors, but rod photoreceptors are positioned behind these reflectors. This unusual arrangement matches rod and cone sensitivity for detecting color-mixed stimuli, whereas the photoreceptor grouping renders the fish insensitive to spatial noise; together, this enables more reliable flight reactions in the fish's dim and turbid habitat as compared with fish lacking this retinal specialization. [ABSTRACT FROM AUTHOR]

It was established that the electric activity of slightly electric fish Gnathonemus leopoldianus and the motion activity of somiks Hoplosternum thoracatum and cockroaches Blaberus craniifer, which were kept in a thermally stabilized room, regularly change throughout the year. Changes in the activities of different species of animals are coordinated. In all of the cases, the activity maximum falls on the spring-summer period. Possible factors responsible for seasonal variations in the electric and motion activities are discussed, and their forms are compared with the character of seasonal variations in different geophysical processes. [ABSTRACT FROM AUTHOR]

The receptive field of a sensory neuron is known as that region in sensory space where a stimulus will alter the response of the neuron. We determined the spatial dimensions and the shape of receptive fields of electrosensitive neurons in the medial zone of the electrosensory lateral line lobe of the African weakly electric fish, Gnathonemus petersii, by using single cell recordings. The medial zone receives input from sensory cells which encode the stimulus amplitude. We analysed the receptive fields of 71 neurons. The size and shape of the receptive fields were determined as a function of spike rate and first spike latency and showed differences for the two analysis methods used. Spatial diameters ranged from 2 to 36 mm (spike rate) and from 2.45 to 14.12 mm (first spike latency). Some of the receptive fields were simple consisting only of one uniform centre, whereas most receptive fields showed a complex and antagonistic centre-surround organisation. Several units had a very complex structure with multiple centres and surrounding-areas. While receptive field size did not correlate with peripheral receptor location, the complexity of the receptive fields increased from rostral to caudal along the fish’s body. [ABSTRACT FROM AUTHOR]

Gnathonemus petersii and other African weakly electric fish (Mormyridae) produce electric signals in order to sense their environment, a process called active electrolocation. During active electrolocation electrical images of objects in the environment are cast onto a mosaic of electroreceptors, which are embedded in the animal's skin. In Gn. petersii and four other species of mormyrid fish, the densities of electroreceptor organs (mormyromasts and ampullary organs) were determined at various skin regions, including the chin, the nasal region and the back. In all species investigated, the highest mormyromast densities were found at the chin, followed by the nasal region. In addition to this comparative approach, we investigated the electroreceptive epidermis of Gn. petersii in more detail. At the moveable chin appendix, the Schnauzenorgan, scanning electron microscopy analysis helped to elucidate the mosaic-like distribution and the morphology of the electroreceptor organs and their embedding in the epidermis. Because the number of mormyromasts increased very little when fish got bigger, receptor organ densities decreased with standard length. Mormyromast density at the Schnauzenorgan, especially at its tip, highly exceeded that at all other skin regions. Along the Schnauzenorgan, receptor densities decreased exponentially from the tip towards the base. At the nasal region, mormyromast densities were more than three times higher compared to the rest of the fish's head and trunk. A similar distribution to that of the mormyromasts was found for the ampullary electroreceptor organs, which are used for passive electroreception. Our findings support the hypothesis that at least in Gn. petersii the Schnauzenorgan and the nasal region are electroreceptive foveae. [ABSTRACT FROM AUTHOR]

Abstract: The African weakly electric fish Gnathonemus petersii is well known for its electrosensory capabilities. These animals can detect and distinguish objects through active electrolocation in complete darkness. Because of their nocturnal lifestyle, a low contribution of vision for orientation and object detection has been expected. However, as we show in this review, the retina of G. petersii is highly specialized with hundreds of rods and tens of cones grouped together in bundles in a complex way, ensheathed by a tapetum lucidum. The structure of the bundles goes beyond what would be expected if only photon catch was supposed to be increased. During daytime, the structure of these “macro-receptors” changes dramatically depending on retinomotor movements. During the day, the rods and cones are located in different compartments of the bundle, separated by a narrow canal in the form of a “bottle neck”. Investigations on cell structure and neurochemistry in the retina indicate a general organization that is simpler in terms of bipolar and ganglion cell diversity than in tetrachromatic species such as goldfish, yet similar in terms of neurochemical differentiation of amacrine cells. In both respects, the inner retina of the elephantnose fish bears the greatest similarity to catfish and some deep-sea fish retinae. Neuronal circuits and bundle structure give hints of possible adaptations for contrast and/or movement detection. Behavioral experiments suggest that, in contrast to the vision specialists Lepomis gibbosus, pattern detection of G. petersii is not affected by higher spatial frequencies. A pattern of low spatial frequencies, however, was equally well detected by G. petersii and L. gibbosus. Optomotor response experiments indicate that motion vision is important for Gnathonemus, narrowing down the search for the functional specialization of the Gnathonemus retina and providing a starting point for work on multisensory integration in these fish. [Copyright &y& Elsevier]

We critically compared local populations of the bulldog fish, Marcusenius macrolepidotus (Peters 1852), from different watersheds, from the furthest south (28° South, South Africa) to the Equator in Kenya. We ascertained allopatric differentiation from topotypical M. macrolepidotus from the Lower Zambezi River (Mozambique) in morphology, electric organ discharges, and molecular genetics for: (1) samples from the Okavango and Upper Zambezi Systems (Botswana and Namibia), (2) samples from South Africa's rivers draining into the Indian Ocean, and (3) samples from the East African Tana River (Kenya). Significant genetic distances in the mitochondrial cytochrome b gene and differing ISSR-PCR profiles corroborate differentiation between the four taxa. We resurrect M. pongolensis (Fowler, 1934) for South Africa (sample 2), and M. angolensis (Boulenger, 1905) for the Quanza River/Angola. We recognize M. altisambesi sp. n. for the Upper Zambezi/Okavango specimens (sample 1), and M. devosi sp. n. for those from Kenya (sample 3). [ABSTRACT FROM AUTHOR]

Weakly electric fish orient at night by employing active electrolocation. South American and African species emit electric signals and perceive the consequences of these emissions with epidermal electroreceptors. Objects are detected by analyzing the electric images which they project onto the animal’s electroreceptive skin surface. Electric images depend on size, distance, shape, and material of objects and on the morphology of the electric organ and the fish’s body. It is proposed that the mormyrid Gnathonemus petersii possesses two electroreceptive “foveae” at its Schnauzenorgan and its nasal region, both of which resemble the visual fovea in the retina of many animals in design, function, and behavioral use. Behavioral experiments have shown that G. petersii can determine the resistive and capacitive components of an object’s complex impedance in order to identify prey items during foraging. In addition, fish can measure the distance and three-dimensional shape of objects. In order to determine object properties during active electrolocation, the fish have to determine at least four parameters of the local signal within an object’s electric image: peak amplitude, maximal slope, image width, and waveform distortions. A crucial parameter is the object distance, which is essential for unambiguous evaluation of object properties. [ABSTRACT FROM AUTHOR]

Electroreceptive fish detect nearby objects by processing the information contained in the pattern of electric currents through the skin. The distribution of local transepidermal voltage or current density on the sensory surface of the fish's skin is the electric image of the surrounding environment. This article reports a model study of the quantitative effect of the conductance of the internal tissues and the skin on electric image generation in Gnathonemus petersii (Günther 1862). Using realistic modelling, we calculated the electric image of a metal object on a simulated fish having different combinations of internal tissues and skin conductances. An object perturbs an electric field as if it were a distribution of electric sources. The equivalent distribution of electric sources is referred to as an object's imprimence. The high conductivity of the fish body lowers the load resistance of a given object's imprimence, increasing the electric image. It also funnels the current generated by the electric organ in such a way that the field and the imprimence of objects in the vicinity of the rostral electric fovea are enhanced. Regarding skin conductance, our results show that the actual value is in the optimal range for transcutaneous voltage modulation by nearby objects. This result suggests that "voltage" is the answer to the long-standing question as to whether current or voltage is the effective stimulus for electroreceptors. Our analysis shows that the fish body should be conceived as an object that interacts with nearby objects, conditioning the electric image. The concept of imprimence can be extended to other sensory systems, facilitating the identification of features common to different perceptual systems. [ABSTRACT FROM AUTHOR]

An examination of the permanent bony structures of the anal fin complex in the mormyrid fish,Gnathonemus petersii, revealed two new structural sexual dimorphisms: longer proximal pterygiophores and wider anal fin rays in males than in females. Both structures are thought to facilitate the male’s courtship-associated anal fin reflex. Adult male mormyrid fishes are characterized by a dorsally directed indentation of the posterior body wall(anal fin indentation). The expression of this indentation in males, presumably driven by anal fin musculature, was correlated with the fish’s gonadal state: large indentations were associated with high gonado-somatic indices and small indentations with low indices. [ABSTRACT FROM AUTHOR]

Spike timing-dependent plasticity that follows anti- Hebbian rules has been demonstrated at synapses between parallel fibers and inhibitory interneurons known as medium ganglionic layer (MG) neurons in the cerebellum- like electrosensory lobe of mormyrid fish. This plasticity is expressed when presynaptic activation is associated with a characteristically broad, postsynaptic action potential, lasting 7–15 ms, occurring within a window of up to 60–80 ms following synaptic activation. Since the site of plastic change is presumably in the apical dendrites, it is important to know where, when and how this broad spike is generated and the manner in which such events propagate within the intrinsic network of the electrosensory lobe. The electrosensory lobe has a strict layered organization that makes the preparation suitable for one dimension current source density analysis. Using this technique in an ‘in vitro’ interface slice preparation, we found that following either parallel fiber stimulation or an orthogonal field stimulus, a sink appeared in the ganglionic layer and propagated into the molecular layer. Intracellular records from MG somata showed these stimuli evoked broad action potentials whose timing corresponds to this sink. TTX application in the deep fiber layer blocked the synaptically evoked ganglionic layer field potential and the ‘N3’ wave of the outer molecular layer field potential simultaneously, while the molecular layer ‘N1’ and ‘N2’ waves corresponding to synaptic activation of the apical dendrites remained intact. These results confirm the hypothesis that the broad spikes of MG cells originate in the soma and propagate through the molecular layer in the apical dendritic tree, and suggest the possibility that this backpropagation may contribute to ‘boosting’ of the synaptic response in distal apical dendrites in certain circumstances. [ABSTRACT FROM AUTHOR]

Nature has developed a stunning diversity of sensory systems. Humans and many animals mainly rely on visual information. In addition, they may use acoustic, olfactory, and tactile cues for object detection and spatial orientation. Beyond these sensory systems a large variety of highly specialized sensors have evolved. For instance, some buprestid beetles use infrared organs for the detection of forest fires. The infrared sensors of boid and crotalid snakes are used for prey detection at night. For object detection and spatial orientation many species of nocturnal fish employ active electrolocation. This review describes certain aspects of the detection and processing of infrared and electrosensory information. We show that the study of natural exotic sensory systems can lead to discoveries that are useful for the construction of technical sensors and artificial control systems. Comparative studies of animal sensory systems have the power to uncover at least a small fraction of the gigantic untapped reservoir of natural solutions for perceptive problems. [ABSTRACT FROM AUTHOR]

Mormyrid fish use active electrolocation to detect and analyze objects. The electrosensory lateral line lobe in the brain receives input from electroreceptors and an efference copy of the command to discharge the electric organ. In curarized fish, we recorded extracellularly from neurons of the electrosensory lateral line lobe while stimulating in the periphery with either a local point stimulus or with a more natural whole-body stimulus. Two classes of neurons were found: (I) three types of E-cells, which were excited by a point stimulus; and (2) two types of I-cells, which were inhibited by point stimulus and responded with excitation to the electric organ corollary discharge. While all neurons responded to a point stimulus, only one out of two types of I-units and two of the three types of E-units changed their firing behavior to a whole-body stimulus or when an object was present. In most units, the responses to whole-body stimuli and to point stimuli differed substantially. Many electrosensory lateral line lobe units showed neural plasticity after prolonged sensory stimulation. However, plastic effects during whole body stimulation were often unlike those occurring during point stimuli, suggesting that under natural conditions electrosensory lateral line lobe network effects play an important role in shaping neural plasticity. [ABSTRACT FROM AUTHOR]

In pairs of interacting Gnathonemus petersii, a mormyrid electric fish, dominant individuals were larger (longer body). Pairs of interacting fish of similar body size emitted more parallel displays at the onset of an interaction. Over the course of 10 min interactions, head butting increased and parallel display decreased. This decrease occurred primarily in pairs that contained a prior resident and intruder, as compared with two intruders. The patterns of electric organ discharge during parallel display, and the possible sensory modalities mediating this behaviour are discussed. [ABSTRACT FROM AUTHOR]

After injections of the low-molecular-weight tracer neurobiotin into the preeminential nucleus of the brain of the mormyrid fish Gnathonemus petersii, we observed that retrogradely labeled, large fusiform projection neurons (LFd cells) of the deep granular layer of the electrosensory lobe (ELL) were surrounded by 30–50 labeled satellite granular cells. More superficially located projection cells, including large fusiform cells in the superficial granular layer (LFs) and large ganglionic (LG) cells in the ganglionic layer, were never surrounded by labeled satellites. LFd-satellite cells have a small soma (diameter 5–8 μm), a few small dendrites, and an apical axon that terminates in the plexiform and ganglionic layers of the ELL. They contact LFd projection neurons with dendrodendritic, dendrosomatic, and somatodendritic puncta adhaerentia-like appositions, designated here as “neurapses.” In the electron microscope, these contacts resemble synapses without presynaptic vesicles. Because no gap junctions were found between LFd and satellite granule cells, we suggest that the neurapses allow the passage of neurobiotin, though not biocytin or biotinylated dextran amine. These contacts may provide the intermediate substrate for the postulated, but so far unknown, excitatory connection between primary afferent input and LFd projection neurons, via γ-aminobutyric acid (GABA)-ergic granular cells. We suggest that certain puncta adhaerentia-like contacts might not be only adhesive structures and that LFd-satellite granular cells might both excite LFd projection cells via neuraptic contacts of their dendrites and cell bodies and inhibit more superficial LF and LG cells via their GABAergic axonal synapses. Our results suggest that puncta adhaerentia-like contacts could be responsible in some cases for the electrical coupling found electrophysiologically in local inhibitory circuits. J. Comp. Neurol. 468:151–164, 2004. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Thirteen essentially (holo)pelagic species of Mysidacea (Lophogastrida and Mysida), plus five benthopelagic species were taken with vertical plankton hauls (mostly 1000-0 m depth) and by examining the stomach contents of benthopelagic fish (from 550-700 m) in restricted areas of the NE Atlantic Ocean. The families Gnathophausiidae, Lophogastridae, and Eucopiidae are each represented by two species, the Mysidae by 12 species. A first description of the previously unknown male and a supplementary description of the female are given for Longithorax alicei, so far known only from the Canary archipelago. First records for the northern hemisphere are given for two South Atlantic species, Boreomysis bispinosa from the Cape Verde archipelago and Katerythrops resimora from the Canary Islands. Additional new records for the Canary Islands are Gnathophausia zoea, Lophogaster spinosus, and Longithorax nouveli. Among the 12 species of Mysidae examined, ten showed statoliths mineralized with fluorite (CaF), while two Boreomysis species showed comparatively soft, non-mineralized statoliths. Most of the 29 pelagic species so far known from the Selvagens, the Canary, and the Cape Verde Islands belong to the circumtropical deep-water fauna. The local pelagic fauna shows no particular correspondence with that in the Mediterranean, because the two areas have almost nothing but ubiquitous species in common. By contrast, ten benthopelagic species so far recorded from pelagic (plankton) samples off the Canary Islands are endemic in the eastern Atlantic, in most cases including the Mediterranean. [ABSTRACT FROM AUTHOR]

A recently discovered species flock of mormyrid fishes is marked by a striking degree of electric signal diversity among species of rather similar form. We investigated electric organ discharge (EOD) variation in a group of seven, morphologically similar Brienomyrus species within this species flock. All of these forms have blunt snouts. We made quantitative measurements of 25 EOD characters from field recorded signals. Results of principal components analyses using these characters demonstrate that distinct, species-typical EODs are produced by each of the morphologically defined blunt-snouted taxa, consistent with the hypothesis that the EOD plays a role in species recognition. We correctly assigned 30 novel individuals to species on the basis of EOD characters alone using classification functions derived from discriminant function analysis. Landmark-based ordination is a powerful technique for quantifying EOD variation and delimiting species boundaries. This approach will provide an important aid in taxonomic descriptions of new Brienomyrus forms that are still being discovered from the rivers and streams of Gabon. [ABSTRACT FROM AUTHOR]

We report on parapatric speciation in the mormyrid fish, Pollimyrus castelnaui (Boulenger, 1911), from the Okavango and the Upper Zambezi River systems. We recognise samples from the Zambezi River as a distinct species, P. marianne, displaying an eastern phenotype of electric organ discharge (EOD) waveform (Type 3) that is distinct from the western EOD phenotype (Type 1) observed in P. castelnaui samples from the neighbouring Okavango. Samples from the geographically intermediate Kwando/Linyanti River (a tributary of the Zambezi that is also intermittently connected to the Okavango) presented a more variable third EOD phenotype (Type 2). In 13 out of 14 morphological characters studied, the Zambezi River samples differed significantly from P. castelnaui. Morphologically and in EOD characters, the Kwando/Linyanti fish are distinct from both P. castelnaui and P. marianne. Sequence analysis of the mitochondrial cytochrome b gene unambiguously reveals that specimens from the Zambezi River System form a well supported taxon which clearly differs from P. castelnaui from the Okavango (1.5–2.5% sequence divergence). Within specimens from the Kwando–Zambezi System some geographic differentiation can be detected (nucleotide substitutions up to 0.6%); but groups cannot be resolved with certainty. Significant allozyme differences were found between the Okavango and all other EOD types from the Upper Zambezi System, and, within the Zambezi System, between the Kwando (Type 2) and Zambezi (Type 3) individuals. The low Wright's fixation index values, the lack of fixed allele differences, and small genetic distances provide little evidence for speciation between groups within the Zambezi System, but moderate to great fixation index values and significant allele frequency differences were observed between the Okavango and the other fishes. It is concluded that within the Zambezi System, differentiation between Kwando/Linyanti and Zambezi populations (as revealed by morphology and EOD waveform comparisons) is so recent that substantial genetic (allozyme and mitochondrial sequence) differences could not have evolved, or were not detected. [ABSTRACT FROM AUTHOR]

Studies the landmark use and development of navigation behavior in the weakly electric fish Gnathonemus petersii. Key issues of interest; Analysis of pertinent topics and relevant issues; Implications on experimental biology.

The weakly electric fish Gnathonemus petersii detects, localizes, and analyzes objects during active electrolocation even in complete darkness. This enables these fish to lead a nocturnal life and find and identify their prey (small insect larvae) on the ground of their freshwater habitat. During active electrolocation, fish produce a series of brief electric signals, electric organ discharges (EOD), with an electric organ in their tail. Each EOD builds up a stable electric field around the fish, which is distorted only by nearby objects. Field distortions lead to changes of the transepidermal electric current flow at a region of the fish''s electroreceptive skin surface called the ‘electric image’. Within the electric image, locally perceived EODs can be either altered in amplitude or waveform by an object. Fish measure both parameters to assess object properties, such as the capacitive and resistive components of the object''s complex impedance, the object''s size and shape, and its distance from the fish. None of these object properties can be evaluated in isolation, but have to be inferred during parallel processing of electric image spatial and qualitative parameters. Two anterior skin regions of G. petersii appear to possess particular properties for special electrolocation tasks and we therefore refer to them as ‘foveal’ regions. Because of its high electroreceptor density, the electric field geometry around it, and its behavioral use, the ‘nasal region’ between the nares and the mouth at the head of the fish is suggested to be a fovea for long-range guidance and object detection. We propose that the ‘Schnauzenorgan’, a long and flexible chin appendix covered densely with electroreceptor organs, is a second electroreceptive fovea associated with a short-range (food) identification system. Together, these two electric foveae constitute an effective prey detection and identification system. [Copyright &y& Elsevier]

We review modelling and experimental work dealing with the mechanisms of generation of electric image. We discuss: (1) the concept of electric image in the context of the reafference principle; (2) how waveform codes an impedance related qualia of the object image, referred to as “electric colour”; (3) that some characteristics of the spatial profiles generated by pre-receptor mechanisms are suitable for edge detection; (4) which parameters of the spatial profiles provide information for distance discrimination; (5) that electric images are distributed representations of the scene. [Copyright &y& Elsevier]

Explores the use of template-matching by the weakly electric fish, Gnathonemus petersii. Recognition of visual patterns previously viewed from a fixed vantage point; Impact of light intensities; Analysis of characteristics used by the fish to discriminate the visual training patterns.

Saffan[sup ®], previously known as CT1341, is an injectable steroid anesthetic for use in cats and monkeys. It is also suited to induce anesthesia in fishes. It has the convenient property to induce anesthesia of the central nervous system, and to leave the sensory system of the integument operational. The active constituents are alphaxalone and alphadolone. A dose of 24 mg/kg i.m. is sufficient for 2 to 3 hours narcosis in fish of several hundreds of grams. For small specimens administration via bath-water in doses of 2 to 4.8 mg/l for induction and half this dose for maintenance are advisable. In catfish, Ictalurus nebulosus and I. melas, of 100 g or more the induction time after i.m. injection with 21 mg/kg is about 20 min and independent of weight or temperature. The recovery time varies with temperature from 213 min at 13°C to 19 min at 19°C. In 1000 g catfish, Clarias gariepinus, the onset of surgical anesthesia occurs after 26 min on average at doses of 24 mg/kg at 24°C. In 5 g catfish, Kryptopterus bicirrhis, 4.8 mg/l bath water at 25°C makes the opercular movements disappear after 5 min. For 15 cm TL Gnathonemus petersii a good induction dose is 2 mg/l bathwater. After 20 minutes at 23°C surgical narcosis is reached. [ABSTRACT FROM AUTHOR]

Demonstrates the echo response of the weakly electric fish Gnathonemus petersii to series of pulses. Response to double pulses with the echo interval between them; Spontaneous discharge interval; Effects of the delay of the double pulse from the last spontaneous electric organ discharge; Adaptation effect.

East African and south African churchills (Petrocephalus, Mormyridae) were synonymised in 1959 to become members of a single species of subcontinental, southern African distribution, Petrocephalus catostoma (Günther, 1866). By comparison with the type material for P. catostoma from the Ruvuma River and P. stuhlmanni from the Ruvu River, both of East African origin, we confirm the South African form of churchill to represent a new species, P. wesselsi, ranging from the northern Limpopo and Incomati systems south to the Pongola River (Natal) as its southern limit. We also compared churchills from the Sabie River (25° S, South Africa, Incomati system) with churchills from the Upper Zambezi River (17° S, Namibia), using electric organ discharges (EODs) and morphology. The duration of an EOD pulse of the South African form (N = 39; 943.2±S.E. 18.82 µs) is, on average, more than twice that of the Upper Zambezi form (N = 37; 436.6±15.1 µs), and the amplitude of the second head-positive phase (P2 phase relative to P1 = 1) significantly weaker (0.133 ± 0.0005 vs. 0.472 ± 0.002 for Upper Zambezi males, 0.363 ± 0.03 for Upper Zambezi females). In contrast to the Upper Zambezi form, the EOD of the South African form exhibits no difference between the sexes. Fish from the two origins differ significantly in 11 out of 14 anatomical characters studied, confirming molecular genetic differentiation on the species level. [ABSTRACT FROM AUTHOR]

Presents a study which examined the electrophysical properties of the efferent neurons of the electrosensory lateral line lobe (ELL) in mormyrid electric fish Gnathonemus petersii. Materials and methods used in the study; Intrinsic network of ELL; Voltage dependent channels in efferent neurons and ganglion cells.

This was an investigation to determine the feasibility of an autoregressive (AR) model for establishing characteristic parameters from recorded occlusal sounds and develop their classification. Thirty four normal subjects with intact natural dentitions were selected for the study. The subjects' occlusal sounds from both sides of their faces respectively were sampled, and the gnathosonic classification (Class A, B and C) was established by observing the original recorded wave pattern and measuring the duration. Then, a 20 order AR model was calculated with the collected data, and the AR model coefficients were found to be similar to the indices of Bayes' discriminatory analysis. The total conformation rates of the modelled left and right occlusal sounds to the classification, estimated by Bayes' discriminant functions were 97.06% and 88.24% respectively. AR coefficients representing the characteristics of human occlusal sounds can be helpful in their classification and allow computer diagnosis of occlusal disorders. [ABSTRACT FROM AUTHOR]

Presents a study investigating electric image generation in the mormyrid fish Gnathonemus petersii's. Methodology and materials used to conduct the study; Measurements of the fish's skin impedance; Information on the morphological characteristics of Gnathonemus petersii; Findings of the study.

Examines adult weakly discharging electric fish Gnathonemus petersii for sex differences in the waveform of their electric organ discharge and in external morphology. Communication of sex differences; Steroid-dependence of durations of the fish's electric discharge.

1. Seven isolated G. petersii resting in their daytime hiding-places were stimulated via a dipole model (Fig. 1 a) with previously tape-recorded electric organ discharge (EOD) patterns in an attempt to determine whether G. petersii distinguishes two different intraspecific EOD patterns, rest and attack. 2. Rest pattern A was characterized by a broad distribution of EOD intervals, a low mean discharge rate (8 Hz, Fig. 3), and a long period of significantly positive autocorrelation (2 s, Fig. 4a). Accordingly, the spectrum of EOD rate fluctuations showed a low frequency range (0.005 to 0.12 Hz, Fig. 5a). Attack pattern B was a considerably different EOD interval distribution of high mean discharge rate (25 Hz, Fig. 3), showing a short period of significantly positive autocorrelation (0.8 s, Fig. 4b), only. Here, the spectrum of EOD rate fluctuations was at a considerably higher frequency range (0.09 to 0.47Hz, Fig. 5b). 3. Play-back of attack pattern B elicited significantly more bodily startle responses from the experimental fish (Fig. 6) than did the rest pattern A (Table 1). Also the number of attacks directed at the dipole model was significantly greater during stimulation with attack pattern B (Table 2, Fig. 6). 4. The EOD responses of the experimental fish differed in several respects depending on which stimulation pattern was used. The modes of the pulse rate histograms as well as their spans were lower during play-back of rest pattern A than during stimulation with attack pattern B (average 12.3 vs 16.2 Hz, and average 47 vs 56 Hz, respectively; Fig. 11). Short-term (0.2 s) EOD rate correlations were stronger when the fish were stimulated with rest pattern A than when they were stimulated with attack pattern B (average correlations 0.67 and 0.61, respectively; Figs. 10 and 11). Significant positive correlations were maintained for longer periods of time during rest pattern stimulation than during attack pattern stimulation (average 1.94 and 1.24 s, respectively; Figs. 10 and 11). The spectra of EOD rate fluctuations of the stimulated fish were at lower frequency ranges during rest pattern stimulation than during attack pattern stimulation (average amplitude-spectrum peak frequencies 0.02 and 0.07 Hz, respectively: Figs. 12 and 13). 5. Although maximal cross-correlations from the EOD rates to the stimulus pulse rates were weaker during rest pattern stimulation (average 0.2) than during attack pattern stimulation (average 0.33), significant cross-correlations were maintained for longer periods of time during rest pattern stimulation than during attack pattern stimulation (average 1.78 and 0.92 s, respectively). The lags of maximal cross-correlations were greater during rest pattern stimulation than during attack pattern stimulation (average 2.6 and 0.8 s, respectively; Figs. 14 and 15). 6. The results clearly showed that at least two specific EOD time patterns encode different 'messages' in the intraspecific communication system of G. petersii. [ABSTRACT FROM AUTHOR]