Electric Catfish Research Articles

Two proteocephalid cestodes in the fish Malapterurus electricus and Heterobranchus bidorsalis from Lake Nasser, Egypt: a morphological, molecular, and histopathological study

Despite the importance of the electric catfish (Malapterurus electricus) and the African giant catfish (Heterobranchus bidorsalis) in the foodweb of Lake Nasser, Egypt, little is known about their diseases and parasitic fauna. This work describes, for the first time, cestodiasis in M. electricus and H. bidorsalis. Corallobothrium solidum and Proteocephalus sp. were identified morphologically and molecularly from M. electricus and H. bidorsalis, respectively. Using PCR, sequencing, and phylogenetic analysis, the two cestodes shared rRNA gene sequence similarities yet were unique and the two new sequences for the proteocephalid genera were submitted to the GenBank database. The prevalence of infection was 75% and 40% for the two fish species, respectively. Infections significantly increased in the summer and spring and were higher in female fish than in male fish. The intestine was the preferred site of the two adult cestodes. However, in the case of C. solidum some larval cestodes were found outside the intestine in between the skin and abdominal musculature, attached to the mesentery, and within intestinal tunica muscularis. Desquamation of the intestinal epithelium and inflammation at the site of infection in addition to congestion of the intestinal wall of the tapeworm infected fish were evident, indicating that C. solidum and Proteocephalus sp. impacted the infected fish. The larval stages of C. solidum attempted to penetrate the intestine and sometimes they were encircled within fibrous layers infiltrated with inflammatory cells. The infected fish’s musculature was free of cestode infections. Preventive measures should be implemented to prevent the spread of infections.

Cellular patterning and cyto-architectural organization of the skin of electric catfish (Malapterurus electricus, Siluriformes) with a particular emphasis on its ampullary electroreceptor

The functional morphology of the skin of Malapteruridae is presumably evolved to cope with a diversified range of ambient physiological, environmental, and behavioral conditions. Herein, we firstly characterized the microstructures and intriguing patterning of the skin of twelve adult electric catfish (Malapterurus electricus, Malapteruridae) using histological, histochemical, immunofluorescent, and ELISA standard methodology. The skin comprises three sequentially–oriented layers: the epidermis, dermis, and hypodermis with a significantly increased thickness of the former. The epidermis contains four types of cells: the surface epithelial cells, mucous cells, granular cells, and club cells. We defined distinctive ampullary electroreceptors in the outer epidermis that possess flask-shaped sensory crypt containing electroreceptor cells together with vertical collagen rods. Dermis and hypodermis are composed of connective tissue; however, the former is much more coarse and dense with comparable reactivity for Masson–Goldner trichrome (MT). Placing our data in the context of the limited body of previous work, we showed subtle changes in the expression of mucin subunits together with cytoskeletal fractions of collagens, myosin, F-actin, keratins, and tubulins. Taken as a whole, our results convincingly showed that the skin of M. electricus shares some structural similarities to other Siluriformes, however, it has some functional modifications that are implicated in protection, defense, and foraging behavior.

A chromosome-level genome of electric catfish (Malapterurus electricus) provided new insights into order Siluriformes evolution.

The online version contains supplementary material available at 10.1007/s42995-023-00197-8.

Electric catfish hearts are not immune to electric bolts

Electricity is at once the heart's best friend and fiercest foe. The heart coordinates its own rhythmic beats with repetitive gentle electrical pulses and a sudden jolt of electricity can shock a stopped heart back into action. However, an accidental electric bolt can trigger irregular heartbeats and even fatal heart attacks; electric shocks are generally best avoided. So, how do the hearts of electric catfish (Malapterurus beninensis) that stun prey with 300 V discharges protect the delicate organ? Having previously discovered that the muscles of the extraordinary fish are somehow immune to their own violent electrical discharges, Georg Welzel and Stefan Schuster from the University of Bayreuth, Germany, wanted to know how vulnerable the catfish heart is to powerful electric currents.The duo removed the still-beating organ from a catfish and placed it in liquid laced with sugar and salts to keep the organ alive as they recorded the heart's ECG to find out whether the resilient fish had somehow modified the electrical impulses that regulate the heartbeat to withstand life-threatening shocks. However, when the pair compared the electric catfish's ECG to that of a goldfish, the charts were virtually indistinguishable. The catfish had not altered its ECG for protection. And, when Welzel and Schuster checked how responsive the electric catfish's heart is when mildly stimulated, a 0.12 mA current was sufficient to trigger a regular heartbeat, identical to the goldfish heart's stimulation threshold. But the real test came when the pair checked how resilient the catfish heart was to more significant electric shocks – sufficient to trigger a life-threatening irregular heartbeat in other fish – and surprisingly, the electric catfish hearts were equally as vulnerable. A 3.03 mA shock was sufficient to send catfish and goldfish hearts racing erratically. Even though electric catfish are immune to the fatal power of their own bolts of electricity, their hearts appear to be as vulnerable as the hearts of any creature they intend to stun.So, how do the extraordinary river dwellers protect their hearts from their own lethal discharges? Schuster suggests that the heart and other vulnerable tissues, such as the brain and sensory organs, could be wrapped in insulation; however, he has yet to find any evidence of such a material. ‘Either the hypothetical insulators are highly efficient or the actual mechanism of how such layers protect the hearts of living electric catfish is more complex’, Welzel says. Meanwhile, electric catfish continue to be immune to their own deadly discharges regardless of vulnerability at the heart of the matter.

Electric catfish hearts are not intrinsically immune to electric shocks.

High voltage electric shocks cause life threatening cardiac injuries such as sudden cardiac standstill or severe myocardial injury. Here, we analysed the physiology of the heart of the strongly electric catfish (Malapterurus beninensis) that stuns prey with high-voltage shocks but is immune to its own, as well as external, high-voltage shocks. Neither a detailed analysis of the electrocardiogram nor the structure of the heart indicated a specialized cardiac conduction system. Using a suitable perfusion system, we discovered that, despite its immunity in vivo, the explanted heart of electric catfish can readily be activated by external electrical currents and is equally sensitive to electric shock-induced arrhythmias as similar-sized goldfish hearts. The surprise thus is that the electric catfish has a vulnerable heart that requires to be protected by highly efficient but presently unknown means.

Multielectrode registration of episodic discharges generated by weakly electric fishes

Purpose of this study introduces a multielectrode array (MEA) registration system in order to generate electric field images of the episodic discharges generated by weakly electric fish. A multielectrode registration system has several important features: the design of the multielectrode lattice, the amplifier circuit, the choice of reference points for differential measurements, the recovery of the absolute values of the electric field potentials, and the application of principal components analysis. Methods. There are several advantages of our MEA registration as compared with the traditional twoelectrode registration: (a) the signal-to-noise ratio is significantly increased, (b) it is possible to construct the spatial distribution of the electric field for a single electric discharge, (c) the signals’ sources can be easily separated and identified, and (d) quantitative data on the electrical potential distribution can be obtained throughout the entire experimental tank. Results. The results illustrate an example of applied MEA registration. Electric discharges were recorded from a weakly electric catfish, Clarias gariepinus, using an array of 8 x 8 electrodes at a sampling rate of 20 kHz. Data show oscillograms and two-dimensional plots of the spatial distribution of the electrical field.

Efficient high-voltage protection in the electric catfish.

For thousands of years, starting with detailed accounts from ancient Egypt, the African electric catfish (Malapteruridae) has been renowned for its ability to hunt and to defend itself with powerful electric shocks. Surprisingly, the degree to which electric catfish are protected against their own or external electric shocks, how specific any protection would be to the species-specific waveform and whether a discharging catfish has to actively prepare for the onset of its high-voltage discharges has never been analysed. Here, we used digital high-speed video to record catfish during their own discharges or as they were exposed to external discharges, employing goldfish to carefully calibrate the efficiency of all discharges. Electric catfish show a remarkable degree of protection against high voltages: both self-produced and external electric shocks that heavily affected control goldfish failed to evoke involuntary muscle contraction or to affect sensorimotor processing. Even a commercial electrofishing device, set to efficiently immobilise and narcotise fish, failed to have any effect on the electric catfish. Our findings rule out several protective mechanisms and demonstrate a highly efficient and versatile shielding whose nature is presently unclear.

High-voltage catfish immune to their own shocks

Malapterurus beniensis may look like a harmless catfish lounging on the bottom of a tank, but these creatures are far from benign. Packing a powerful 300 V electric shock, the fish usually reserve their pyrotechnics for stunning prey. ‘We always wear thick rubber gloves when handling the fish’, chuckles Stefan Schuster from the University of Bayreuth, Germany, admitting that he and Georg Welzel once tried holding a small catfish without gloves: ‘The shock was surprisingly strong and felt like touching an electric fence’, he recalls. But how do electric catfish withstand their self-administered shocks, which knock out the hearts and nervous systems of their victims? Do the catfish brace themselves to withstand their own electrical discharges, or are they somehow immune? Intrigued by the fish's electrical resilience, Schuster and Welzel obtained two of the shocking creatures to find out how they and their victims deal with an electric jolt.Turning the water to a slow flow to cajole the idle catfish off the bottom of the tank, Welzel gently brushed their tails with a paint brush to startle them into electrical action. But, when he scrutinised movies of the catfish's manoeuvres, they were completely unperturbed by their electric discharges. In contrast, goldfish swimming nearby went into a spasm, flinging their pectoral fins wide in addition to contracting their bodies, before recovering and going on their way. Even more surprisingly, the catfish were equally unconcerned when Welzel zapped the water with an electrofishing probe, never writhing nor twitching. ‘It was surprising that they were equally immune to external discharges that they could not prepare for and were designed specifically to paralyse fish’, Schuster recalls.The catfish's muscles were unaffected by high-voltage electric fields, but it still wasn't clear whether their brain and nervous system were also protected from the effects of electricity. The duo needed to find a way of startling the fish into releasing a bolt of electricity, after sensing the disturbance and processing it in the brain. They reasoned that if the catfish's nervous system was not protected from electric fields, then the speed and timing of the catfish's electrical discharge would be affected if the animal was sitting in an external electric field when startled. However, if the catfish's brain and nervous system were somehow protected, the presence of an external electric field would make no difference to their startled electrical outburst.‘We tested various visual and acoustic stimuli’, says Schuster, recalling how the pair eventually settled on a 300 Hz blast of sound, which reliably startled the fish into pulsing electrically. ‘We had to wear ear defenders’, Welzel laughs. Then, Welzel simultaneously gave the fish an external electric shock while startling them, in an attempt to get them to let their guard down. However, the catfish were completely impervious to the additional electric field, producing startled electric flashes that were indistinguishable from their usual shocking response. They were not steeling their nervous systems in preparation for the disruptive effects of their high-voltage pulses – they were somehow immune.‘Electric catfish show a remarkable degree of protection against high voltages’, says Welzel, who suspects that the extraordinary fish are insulated in some way against their own electric fields. And Schuster adds that the catfish's high-voltage resilience is even more paradoxical, as they are also exquisitely fine-tuned to the weak electric currents generated by the bodies of their prey. A conventional insulator would prevent the catfish from sensing their food, presenting Schuster and Welzel with another mystery to solve.

Characterization of 28S rRNA sequences of cestoda parasite Electrotaenia malapteruri Fritsch, 1886 from the Electric catfish Malapterurus electricus (Siluriformes: Malapteruridae)

Proteocephalids are cestoda parasites that mostly infect freshwater fish. The present study was carried out to investigate the presence of proteocephalids infecting the electric catfish Malapterurus electricus from Lake Manzala, Kafr El-Sheikh Governorate, Egypt. Morphological characterization revealed the present parasite is a cestoda belonging to the genus Electrotaenia. Morphologically, the recovered worms were characterized by an elongated body measuring 100–127 (120 ± 2) mm long and 0.92–2.11 (2.76 ± 0.1) mm wide. The anterior part of the worm was obvious terminated at a spherical scolex measured 1.12–1.91 (1.72 ± 0.01) mm long and 1.12–1.65 (1.42 ± 0.01) mm wide with a rostellum-like apical organ equipped by 5–6 irregular rows of minute hooklets, as well as four uniloculate suckers with a diameter of 0.13–0.15 (0.14 ± 0.01) mm and covered with microtriches. A long unsegmented neck was observed followed by acraspedote and anapolytic strobila consisted of 85–120 proglottids divided into 50–58 immature, 12–19 mature, and up to 49 gravid proglottids. Molecular characterization based on 28S rRNA sequences was done to confirm the taxonomy of this parasite based on its morphology. It was observed that there was a close identity up to 72.0% with other protocephalid species obtained for comparison from the GenBank. Also, the data obtained revealed that there was high blast scores and low divergence between the present parasite and previously described Electrotaenia malapteruri (acc. no. JX477434). Phylogenetic analysis showed that the parasite sequence in conjunction with existing data investigates the placement of this protocephalid species within Proteocephalidea. It was shown that the present species is deeply embedded in the genus Electrotaenia with close relationships to other Electrotaenia malapteruri as a putative sister taxon.

Morphological re-description of Electrotaenia malapteruri (Cestoda: Proteocephalidae) and Dujardinnascaris malapteruri (Nematoda: Heterocheilidae) infecting the Electric catfish Malapterurus electricus and heavy metal accumulation in host and parasites in relation to water and sediment analysis in Lake Manzala, North Delta, Egypt.

Parasites are one of the most serious limiting factors in aquaculture. The Electric catfish Malapterurus electricus was subjected to study the prevalence and mean intensity of parasitic infections throughout the whole year of 2015. Heavy metals accumulation in host fish and parasites were determined in relation to water quality and sediments of two different sites of Lake Manzala (Manzala and Bahr El-Baqar), Egypt. A total of 100 specimens of Electric catfish were collected and examined for the presence of helminth parasites. Two parasite species were recovered and morphologically identified. These were cestoda Electrotaenia malapteruri and nematode Dujardinnascaris malapteruri. Heavy metal analysis in water and sediments showed that measured heavy metals in Bahr El-Baqar were found in risky levels higher than permissible limits and Manzala site. Sediments were found to contain a higher level of metals than water samples. Heavy metals accumulation in recovered parasites and their host were also determined and showed significantly higher concentrations in parasites compared to their host tissues. According to bioconcentration factors, E. malapteruri showed that highest accumulation rate for all recorded elements up to 302. Essential elements like Cu and Fe were found in significantly higher concentrations in D. malapteruri, whereas E. malapteruri accumulated elements Cd, Pb, Ni, Mn, Zn and Ca to a significantly higher degree. Accordingly, the ratios (C[D.malapteruri]/C[E. malapteruri]) for most essential elements were higher than 0.5. Therefore, fish cestodes can be regarded as useful bio-indicators more than nematodes when evaluating the environmental pollution of aquatic ecosystems by heavy metals.

Agonistic sounds and swim bladder morphology in a malapterurid electric catfish

AbstractSeveral catfish families possess an elastic spring apparatus (ESA) morphology that is assumed to function as a swim bladder drumming sound production mechanism. Although they have an ESA, drumming sounds in the electric catfish (Malapteruridae) have not been described. We have recorded several different sound types in Malapterurus beninensis and we examined the morphology of the swim bladder, the ESA and the ultrastructure of the protractor muscle. The protractor muscle contains small rounded muscle fibers with abundant mitochondria, narrow myofibrils, elaborated sarcoplasmic reticula and sometimes sarcoplasmic cores. Contractions of the protractor muscle should pull the Müllerian ramus (MR) and attached swim bladder anteriorly. Further, the MR possesses an anterior fulcrum that abuts upon the vertebral complex. Several sound types were elicited during agonistic interactions in the laboratory. We observed ratchet, click train and mouth sounds. Mouth sounds are single event, low‐frequency (mean dominant frequency 176 Hz) sounds that coincide with a bite‐like motion. Ratchet and click sounds are high‐frequency (mean dominant frequency 1568 and 3739 Hz, respectively) and occur in trains. Ratchet and click train sound characteristics are not indicative of a muscle‐driven drumming sound predicted by ESA morphology. We propose several hypotheses for these sound production mechanisms. Click sounds, in particular, could result from gas movement through the neck between the anterior and posterior swim bladder chambers.

A New Genus and Species of Proteocephalidean (Cestoda) From Clarias Catfishes (Siluriformes: Clariidae) in Africa

A new proteocephalidean cestode is described from 2 catfishes, Clarias gariepinus (type host) and C. cf. anguillaris (Siluriformes: Clariidae), from Ethiopia (type locality), Sudan, Tanzania, and Zimbabwe, and a new genus, Barsonella, is proposed to accommodate it. The genus belongs to the Proteocephalinae because its genital organs (testes, ovary, vitellarium, and uterus) are situated in the medulla. Barsonella lafoni, the type and only species of the new genus, is characterized mainly by the possession of an additional opening of each sucker; circular musculature on the anterior margin of suckers, serving as a sphincter; a small thin-walled glandular apical organ; absence of well-developed osmoregulatory canals in mature, pregravid, and gravid proglottids; and a large strobila, up to 173 mm long and 3.2 mm wide. Species of Marsypocephalus Wedl, 1861 (Marsypocephalinae), other large-sized proteocephalidean tapeworms occurring sympatrically in African catfishes (Clarias and Heterobranchus) and also possessing a sphincter-like, circular musculature on the anterior part of suckers, differ from B. lafoni in the absence of an additional sucker opening and glandular apical organ, the cortical position of the testes, well-developed osmoregulatory canals throughout the strobila, and a large cirrus sac. Proteocephalus glanduligerus (Janicki, 1928), another cestode parasitic in Clarias spp. in Africa, is much smaller than B. lafoni (maximum length 15 mm), has suckers without additional opening and circular musculature on the suckers, a large-sized glandular organ, much larger than suckers, and well-developed osmoregulatory canals. Comparison of partial sequences of the 28S rRNA gene for 7 samples of B. lafoni from 2 different hosts and 4 localities in Ethiopia, Sudan, and Tanzania has shown a very low genetic variability. In a limited phylogenetic analysis, B. lafoni formed a clade with Corallobothrium solidum Fritsch, 1886 (Proteocephalidae: Corallobothriinae), an African electric catfish parasite. This clade was the sister group of almost all Neotropical taxa from pimelodid and other catfishes.

Fin-fishes in Yorùbá natural healing practices from southwest Nigeria

Natural healing treatment recipes from southwest Nigeria were examined for fin-fishes of ethnomedical importance. Fifteen families of 19 genera were identified with members found either in marine, fresh or brackish waters. Two thousand two hundred and eighty-five recipes were examined, 9.11% contained fin-fish or its derivative as component. Fertility/conception-related medical conditions have highest proportion of recipes (26.26%) with fish/derivatives as inputs. One hundred and forty-one recipes were examined for fertility-related conditions, the highest for any medical condition during this study. Clarias sp. (Clariidae) (catfish) recorded the highest rate of use (78.94%) followed by Malapterurus electricus (Malapteruridae) (electric catfish) with 5.26%. Fin-fishes/derivatives were observed to have both physical and spiritual activities in treatment preparations. Most of the fish species were in need of conservation interventions.

Semicystic spermatogenesis and biflagellate spermatozoon ultrastructure in the Nile electric catfish Malapterurus electricus (Teleostei: Siluriformes: Malapteruridae)

AbstractSpermatogenesis and spermatozoon ultrastructure in the Nile electric catfish Malapterurus electricus are described using scanning and transmission electron microscopy. Although the testis organization conforms to the ‘unrestricted’ spermatogonial type, the species has a rare type of spermatogenesis not previously described among catfishes, ‘semicystic’, in which the cyst ruptures before the spermatozoon stage. Spermiogenesis also involves some peculiar features such as condensation of the chromatin in the posterior part of the nucleus to form a compact electron‐dense mass with some irregular electron‐lucent lacunae, while the uppermost part of the nucleus is a loose electron‐lucent area, absence of the nuclear rotation and, as a consequence, the centriolar complex and the initial segment of each flagellum arise directly in a position perpendicular to the basal pole of the nucleus, and occurrence of numerous vesicles in the midpiece. In addition, spermiogenesis includes migration of the diplosome and mitochondria to the basal pole of the nucleus, formation of two moderate nuclear fossae, each of which contains the centriolar complex, development of two independent flagella and elimination of the excess cytoplasm. The mature spermatozoon has a more or less round head with no acrosome or acrosomal vesicle, a long midpiece with numerous mitochondria and vesicles and two long tails or flagella having the classical axoneme structure of 9 + 2 microtubular doublet pattern and with no lateral fins and membranous compartment. These findings suggest that the ultrastructural features of spermiogenesis and spermatozoa of M. electricus are synapomorphies of types I and II spermiogenesis and spermiogenesis is closely similar to the type described in the Nile catfish Chrysichthys auratus.

Ultrastructural characters of the spermatozoon of the cestode Corallobothrium solidum Fritsch, 1886 (Cestoda: Proteocephalidea), a parasite of the electric catfish Malapterurus electricus

The fine structure of the mature spermatozoon of the corallobothriine tapeworm Corallobothrium solidum Fritsch, 1886 (Cestoda: Proteocephalidea) from the electric catfish Malapterurus electricus from the Nile River in Egypt was studied by transmission electron microscopy for the first time. The filiform spermatozoon of C. solidum contains two axonemes of unequal length and a typical 9 + "1" trepaxonematan pattern. A single helicoidal crested body (30-200 nm thick) is localized at the anterior extremity of the gamete. The cortical microtubules line the periphery of the cell, largely parallel to the long axis of the spermatozoon and exhibiting signs of twisting at the beginning of region II. The nucleus, in the form of an electron-dense (largely in gametes of testes) and/or fibrous cord (largely in gametes from male reproductive ducts and seminal vesicle), coils in a spiral through the middle part (region III) of the spermatozoon. The cytoplasm contains electron-dense granules in regions II, III and partly in region IV. The cytoplasm of some spermatozoa exhibits an apparently higher electron-density at the end of the nucleated region (III), and continuously toward the middle part of region IV. The anterior and posterior extremities of the spermatozoa have a single axoneme. The ultrastructural features of the mature spermatozoon of C. solidum mostly coincide with those of the spermatozoon of other proteocephalideans, especially the gangesiine Electrotaenia malopteruri parasitizing the same host.

Redescription of Electrotaenia malopteruri (Fritsch, 1886) (Cestoda: Proteocephalidae), a parasite of Malapterurus electricus (Siluriformes: Malapteruridae) from Egypt.

The proteocephalidean cestode Electrotaenia malopteruri (Fritsch, 1886) (Proteocephalidae: Gangesiinae), the type- and only species of Electrotaenia Nybelin, 1942 and specific to the electric catfish Malapterurus electricus Gmelin (Siluriformes: Malapteruridae), is redescribed on the basis of freshly collected material from the River Nile in Egypt. The validity of Electrotaenia is confirmed and some unique characters of this genus, observed in extensive material from different host specimens from Egypt, Sudan, Sierra Leone and Nigeria are first reported or described in detail. Such details include the internal morphology of a rostellum-like apical organ which is disc-shaped with a flat or slightly concave apex, the structure of the ovary which is follicular to reticulate, the structure of the cirrus-sac, the presence of a medio-dorsal band of muscle fibres, and the morphology of the vagina and eggs.

Food composition and digestive enzymes in the gut of the African electric catfish,Malapterurus electricus(Gmelin 1789) (Malapteruridae)

Stomach contents analyses of 330 specimens of the electric catfish, Malapterurus electricus (Gmelin 1789) (standard length, 10.1-30.5 cm) collected in Mahin Lagoon (southwestern Nigeria) established it as a bottom feeder. A preponderance of insects and prey fish, which accounted for 100% occurrence and > 18% of total volume in the stomachs of specimens, suggested a predatory habit. Carbohydrases (amylase, maltase), chitinase, proteases (pepsin, chymotrypsin, trypsin) and lipases were detected in different gut regions with different activity, which correlated with its predatory diet. KEY WORDS: digestive enzymes, stomach contents, food, electric catfish, Malapterurus electricus.

Morphological evidence for the occurrence of two electric catfish (Malapterurus) species in the White Nile and Omo–Turkana systems (East Africa)

Morphological evidence for the occurrence of two electric catfish (Malapterurus) species in the White Nile and Omo–Turkana systems (East Africa)

Morphological evidence for the occurrence of two electric catfish (Malapterurus) species in the White Nile and Omo–Turkana systems (East Africa)

Morphological analysis of 28 Malapterurus specimens collected from the Nile and Omo–Turkana basins revealed two groups. The first was characterized by low vertebral counts (41–44) and numerous gill rakers (14–22) situated along the entire first ceratobranchial, the second group was characterized by high vertebral counts (47–51) and a low number of gill rakers (6–13) situated only on the upper portion of the first ceratobranchial. Through comparison with the type specimens of three currently recognized Malapterurus species and comparison with museum collections from the Nile, Omo–Turkana, and Chad basins, these two groups were identified as M. electricus and M. minjiriya. A principal component analysis of 27 measurements allowed partial discrimination among species. Biogeographic aspects of finding M. minjiriya in the tributaries of the White Nile and in the middle reaches of the Omo River are discussed.

The future of research on electroreception and electrocommunication

Beyond continuation of currently active areas, some less studied ones are selected for predictions of marked advance. (1) Most discoveries will be in cellular components and molecular mechanisms for different classes of receptor or central pathways. (2) More major taxa, possibly birds, reptiles or invertebrates, will be found to have electroreceptive species representing independent evolutionary 'inventions'. (3) Electric organs with weak and episodic electric discharges will be found in new taxa; first, among siluriforms. (4) New examples are to be expected, such as lampreys, where synchronized muscle action potentials sum to voltages in the range of weakly electric fish. Some of these will look like intermediates in the evolution of electric organs. (5) Ethological significance will be found for a variety of known physiological features; e.g. uranoscopids, skates and weakly electric catfish with episodic electric discharges; electroreceptive ability of animals such as lampreys, chimaeras, lungfish, sturgeons, paddlefish and salamanders with Lorenzinian-type ampullae; gymnotiform and mormyrid detection of the capacitative component of impedance. (6) The organization of some higher functions in the cerebellum and forebrain will gradually come to light.