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The present study on some biological aspects of the Mormyridae fishes, was conducted between May and August 2015 in the Upper Sanaga at Lékié Department (Monatélé Town), Center Cameroon. For this purpose, 125 specimens collected by local fishermen were used. Fishes were identified and measured, and their feeding and reproductive parameters were obtained after dissection. The catch composition of 4 species (Campylomormyrus phantasticus, Mormyrops anguilloides, Mormyrus macrophtalamus, Mormyrus tapirus) of Mormyridae identified in the region was very low (17%–30%). The mean ± standard deviation of total weight and total length were 103.14 ± 37.83 g and 27.47 ± 4.84 cm, respectively. The minimum and maximum size (of 21.1 cm and 43 cm) were recorded from C. phantasticus and M. anguilloides, respectively. The mean ± standard deviation of the relative length and mass of the digestive tract were 0.35% ± 0.20% and 5.27% ± 23.20%, respectively confirming that Mormyridae fish species have a strict carnivorous diet and consume prey that are difficult to digest. The size frequency distribution of the Mormyridae fishes showed that the majority of the fish caught are small sizes in classes 23–26 cm and 26–29 cm in C. phantasticus, M. macrophthalamus and M. tapirus. M. anguilloides did not record small specimens, however, it recorded larger sized specimens (41–44 cm) compared to the rest. The sex ratio ranged from 1M: 1.14F (M. anguilloides) to 1M: 4F (M. tapirus), mean 1M: 2.04F has been generally in favour of females. The gonadosomatic index (GSI) was generally low in all species. However, it was higher in females of C. phantasticus and M. anguilloides compared to other species. The hepatosomatic index (HSI) was weakly correlated with the GSI in these species.

The present study on some biological aspects of the Mormyridae fishes, was conducted between May and August 2015 in the Upper Sanaga at Lékié Department (Monatélé Town), Center Cameroon. For this purpose, 125 specimens collected by local fishermen were used. Fishes were identified and measured, and their feeding and reproductive parameters were obtained after dissection. The catch composition of 4 species (Campylomormyrus phantasticus, Mormyrops anguilloides, Mormyrus macrophtalamus, Mormyrus tapirus) of Mormyridae identified in the region was very low (17%-30%). The mean ± standard deviation of total weight and total length were 103.14 ± 37.83 g and 27.47 ± 4.84 cm, respectively. The minimum and maximum size (of 21.1 cm and 43 cm) were recorded from C. phantasticus and M. anguilloides, respectively. The mean ± standard deviation of the relative length and mass of the digestive tract were 0.35% ± 0.20% and 5.27% ± 23.20%, respectively con- firming that Mormyridae fish species have a strict carnivorous diet and consume prey that are difficult to digest. The size frequency distribution of the Mormyridae fishes showed that the majority of the fish caught are small sizes in classes 23-26 cm and 26-29 cm in C. phantasticus, M. macrophthalamus and M. tapirus. M. anguilloides did not record small specimens, however, it recorded larger sized specimens (41-44 cm) compared to the rest. The sex ratio ranged from 1M: 1.14F (M. anguilloides) to 1M: 4F (M. tapirus), mean 1M: 2.04F has been generally in favour of females. The gonadosomatic index (GSI) was generally low in all species. However, it was higher in females of C. phantasticus and M. anguilloides compared to other species. The hepatosomatic index (HSI) was weakly correlated with the GSI in these species. [ABSTRACT FROM AUTHOR]

The elephant-snout fish Mormyrus kannume is one of the known interesting fish in the most interesting man-made lake in Egypt (Lake Nasser). Due to the global conservatory objectives and lake management, this species won scientific and commercial interest as there were no sufficient or recent studies on this species. The present work aimed to study the growth pattern of the elephant-snout fish (M. kannume) from Lake Nasser, Egypt via length-weight relationship, condition factor, growth in age and growth parameters. A total of 645 specimens were monthly collected from the commercial landing sites (Aswan, Garf Hussein and Abu Simbel harbours) from November 2017 to December 2018. The investigations illustarted a wide range of length from 15.3 to 77.5 cm (TL), with an average of 36.3±7.0 cm and a total weight (W) ranging from 25.2 to 2882.5 g, with an average of 360.3±278.6. The length-weight relationship showed negative allometric growth for males, females, and combined sexes. The absolute condition (Kc) showed a higher value during February (0.74±0.06) for males and during April (0.72±0.06), May (0.72±0.09) and July (0.72±0.06) for females. For C. sexes, the highest value was recorded during February (0.72±0.06). The lower Kc was during August for males, females and C. sex. In general, the conditions were located under "1" along the year and recorded an annual average of 0.68±0.072, 0.69±0.70 and 0.68±0.075 for males, females and C. sexes respectively. By using opercula reading, the life span/growth rings of M. kannume were calculated as ten years with a mean length of 17.3, 26.64, 35.11, 42.98, 49.56, 55.91, 61.5, 65.82, 69.66 and 72.54 cm TL, for each age groups from one to ten respectively. The von Bertalanffy growth constants were computed as L8= 89.91 cm TL, K = 0.16 year-1, and to = -0.91. The growth performance index (ϕ) was 3.11 and the longevity of age (t max) was 18.56 years. In spite of the presence of negative allometric growth combined with the lower value of conditions than "1" which may be affected by food and spawning, the others such as aging, growth performance, and age longevity have reflected a satisfied growth pattern in this lake and are valuable for creating a monitoring and management system for M. kannumein Lake Nasser recommending its conservation with require to more studies. [ABSTRACT FROM AUTHOR]

Hybridisation is an important element of adaptive radiation in fish but data are limited in weakly electric mormyrid fish in this respect. Recently, it has been shown that intragenus hybrids (Campylomormyrus) are fertile and are able to produce F2-fish. In this paper, we demonstrate that even intergenus hybrids (Gnathonemus petersii ♂ × Campylomormyrus compressirostris ♀) are fertile. Three artificial reproduction (AR) trials, with an average fertilisation rate of ca. 23%, yielded different numbers of survivals (maximally about 50%) of the F1-hybrids. The complete ontogenetic development of these hybrids is described concerning their morphology and electric organ discharge (EOD). Two EOD types emerged at the juvenile stage, which did not change up to adulthood. Type I consisted of four phases and Type II was triphasic. The minimum body length at sexual maturity was between 10 and 11 cm. Malformations, growth and mortality rates are also described. [ABSTRACT FROM AUTHOR]

Hybridization is widespread in fish and constitutes an important mechanism in fish speciation. There is, however, little knowledge about hybridization in mormyrids. F1-interspecies hybrids between Campylomormyrus tamandua ♂ × C. compressirostris ♀ were investigated concerning: (1) fertility; (2) survival of F2-fish and (3) new gene combinations in the F2-generation concerning the structure of the electric organ and features of the electric organ discharge. These F1-hybrids achieved sexual maturity at about 12–13.5 cm total length. A breeding group comprising six males and 13 females spawned 28 times naturally proving these F1-fish to be fertile. On average 228 eggs were spawned, the average fertilization rate was 47.8%. Eggs started to hatch 70–72 h after fertilization, average hatching rate was 95.6%. Average mortality rate during embryonic development amounted to 2.3%. Average malformation rate during the free embryonic stage was 27.7%. Exogenous feeding started on day 11. In total, we raised 353 normally developed larvae all of which died consecutively, the oldest specimen reaching an age of 5 months. During survival, the activities of the larval and adult electric organs were recorded and the structure of the adult electric organ was investigated histologically. [ABSTRACT FROM AUTHOR]

ABSTRACT We describe the circuit design, construction, and operation of a field-portable electric fish finder (an AC-coupled wide-band differential bio-amplifier with loudspeaker output). This device permits detection and monitoring of the electric organ discharges generated by neotropical gymnotiform fishes (as well as the mormyroid fishes of tropical Africa). Our design is modified from earlier versions to optimize detection performance and stability over a wider range of ambient water conductivity, including under conditions of extremely low conductivity (< ca. 10 μScm-1). Our new electric fish finder design also incorporates complete waterproofing and longer battery autonomy. We provide Gerber and Eagle files made with the electronic design automation software ‘Autodesk Eagle’ to allow researchers to order printed circuit boards directly from commercial manufacturers.

Eavesdropping by electroreceptive predators poses a conflict for weakly electric fish, which depend on their Electric Organ Discharge (EOD) signals both for navigation and communication in the dark. The EODs that allow weakly electric fish to electrolocate and communicate in the dark may attract electroreceptive predators such as catfishes and Electric Eels. These predators share with their prey the synapomorphy of passive electric sense supported by ampullary electroreceptors that are highly sensitive to low-frequency electric fields. Any low-frequency spectral components of the EOD make weakly electric fish conspicuous and vulnerable to attack from electroreceptive predators. Accordingly, most weakly electric fish shift spectral energy upwards or cloak low-frequency energy with compensatory masking signals. Subadults and females in particular emit virtually no low-frequency energy in their EODs, whereas courting males include a significant low-frequency component, which likely attracts females, but makes the signals conspicuous to predators. Males of species that coexist with the most predators tend to produce the least low-frequency signal energy, expressing sexual dimorphism in their signals in less risky ways. In these respects, electric signals follow the classic responses to opposing forces of natural and sexual selection, as exemplified in the visual signals of guppies and the acoustic signals of Túngara frogs. Unique to electric fish is that the electric signal modifications that help elude detection by electroreceptive predators are additions to the basal signal rather than losses of attractive components. These enhancements that enable crypsis are energetically costly, but have also provided the evolutionary substrates for subsequent sexual selection and species identity characters.

We describe the circuit design, construction, and operation of a field-portable electric fish finder (an AC-coupled wideband differential bio-amplifier with loudspeaker output). This device permits detection and monitoring of the electric organ discharges generated by neotropical gymnotiform fishes (as well as the mormyroid fishes of tropical Africa). Our design is modified from earlier versions to optimize detection performance and stability over a wider range of ambient water conductivity, including under conditions of extremely low conductivity (< ca. 10 µScm-1). Our new electric fish finder design also incorporates complete waterproofing and longer battery autonomy. We provide Gerber and Eagle files made with the electronic design automation software 'Autodesk Eagle' to allow researchers to order printed circuit boards directly from commercial manufacturers. [ABSTRACT FROM AUTHOR]

During two brief collecting trips on the White Nile in the area of Kosti and Al Jabalayn in April 2016 and March 2018, 82 fish species from 48 genera and 23 families were recorded. During the 2016 survey, major parts of the type series of the just recently described Labeo latebra Moritz & Neumann, 2017 were collected together with an apparently undescribed Haplochromis species from Kosti. Additionally, a marked variance in syntopic Sarotherodon galilaeus (Linnaeus, 1758) populations was observed during both trips: single specimens from Makhaleif and Kosti differ clearly in head contour, overall body shape and colouration pattern compared to standard Nilo-Sudanian Sarotherodon galilaeus commonly occurring in the White Nile and elsewhere. Enteromius macrops (Boulenger, 1911) and Paradistichodus dimidiatus (Pellegrin, 1904) are reported for the first time from the Main Nile Basin and the rarely encountered mormyrid species Cyphomyrus petherici (Boulenger, 1898) and Petrocephalus keatingii Boulenger, 1901, as well as the small mochokid Mochokus brevis Boulenger, 1906 were confirmed for the White Nile. [ABSTRACT FROM AUTHOR]

The ability to localize communication signals plays a fundamental role in social interactions. For signal localization to take place, the sensory system of the receiver must extract information about distance and direction to the sender from physical characteristics of the signal. In many sensory systems, information from multiple peripheral receptors must be integrated by central sensory pathways to determine the sender location. Here, we asked whether evolutionary divergence in the electrosensory and visual systems of mormyrid fish is associated with signal localization behavior. In mormyrids, differences in the distribution of electroreceptors on the surface of the skin are associated with differences in the midbrain exterolateral nucleus (EL). Species with electroreceptors clustered in three rosettes on both sides of the head have a small and undifferentiated EL. In contrast, EL is enlarged and subdivided into anterior (ELa) and posterior (ELp) regions in species that have electroreceptors broadly -distributed throughout the body. Interestingly, species with EL and clustered electroreceptors also have larger visual systems and higher visual acuity than species with ELa/ELp and broadly distributed electroreceptors. Species with broadly distributed electroreceptors and ELa/ELp approached a simulated conspecific by following the curved electric field lines generated by the electrosensory stimulus. In contrast, a species with small EL and clustered electroreceptors, but an enlarged visual system, followed shorter and straighter paths to the stimulus source. In the central electrosensory system, evoked field potentials in response to stimuli delivered from the left versus the right differed more in EL than in ELa/ELp. Our results suggest that signal localization behavior is associated with differences in sensory specializations. We propose that the distribution of electroreceptors on the body affects the ability of individuals to align parallel to electric field lines and maintain such alignment while approaching the signal source. The spatial resolution of sensory information relayed from the periphery to the midbrain in species with clustered electroreceptors may allow for gross, but not fine, processing of sender location. Furthermore, visual information may play an important role in localizing signaling individuals in species with small EL and clustered electroreceptors. In line with previous studies, we suggest that the physiological and behavioral differences associated with signal localization reflect adaptations to different habitats and social environments. [ABSTRACT FROM AUTHOR]

Mormyrid weakly electric fish produce electric organ discharges (EODs) for active electrolocation and electrocommunication. These pulses are emitted with variable interdischarge intervals (IDIs) resulting in temporal discharge patterns and interactive signaling episodes with nearby conspecifics. However, unequivocal assignment of interactive signaling to a specific behavioral context has proven to be challenging. Using an ethorobotical approach, we confronted single individuals of weakly electric Mormyrus rume proboscirostris with a mobile fish robot capable of interacting both physically, on arbitrary trajectories, as well as electrically, by generating echo responses through playback of species-specific EODs, thus synchronizing signals with the fish. Interactive signaling by the fish was more pronounced in response to a dynamic echo playback generated by the robot than in response to playback of static random IDI sequences. Such synchronizations were particularly strong at a distance corresponding to the outer limit of active electrolocation, and when fish oriented toward the fish replica. We therefore argue that interactive signaling through echoing of a conspecific's EODs provides a simple mechanism by which weakly electric fish can specifically address nearby individuals during electrocommunication. Echoing may thus enable mormyrids to mutually allocate social attention and constitute a foundation for complex social behavior and relatively advanced cognitive abilities in a basal vertebrate lineage. [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]

Mormyrid weakly electric fish have a special electrosensory modality that allows them to actively sense their environment and to communicate with conspecifics by emitting sequences of electric signals. Electroreception is mediated by different types of dermal electroreceptor organs for active electrolocation and electrocommunication, respectively. During electrocommunication, mormyrids exhibit stereotyped discharge sequences and locomotor patterns, which can be induced by playback of electric signals. This raises the question: what sensory information is required to initiate and sustain social interactions, and which electrosensory pathway mediates such interactions? By experimentally excluding stimuli from vision and the lateral line system, we show that Mormyrus rume proboscirostris can rely exclusively on its electrosensory system to track a mobile source of electric communication signals. Detection of electric playback signals induced discharge cessations, followed by double-pulse patterns. The animals tried to interact with the moving signal source and synchronized their discharge activity to the playback. These behaviors were absent in control trials without playback. Silencing the electric organ in some fish did not impair their ability to track the signal source. Silenced fish followed on trajectories similar to those obtained from intact animals, indicating that active electrolocation is no precondition for close-range interactions based on electrocommunication. However, some silenced animals changed their strategy when searching for the stationary playback source, which indicates passive sensing. Social interactions among mormyrids can therefore be induced and mediated by passive reception of electric communication signals without the need for perception of the location of the signal source through other senses. [ABSTRACT FROM AUTHOR]

Abstract: Based on morphological data and analysis of mitochondrial cytochrome b gene and nuclear (S7 intron 1) DNA sequences, the phylogenetic relationships of all Pollimyrus species known from the Omo‐Turkana enclosed basin and Nile system below the Murchison Falls were solved. A mormyrid “Pollimyrus” petherici is distantly related to all other studied Pollimyrus species and clusters together with Cyphomyrus species forming with the later a monophyletic group. Moreover, the West African (but not the Congo River) populations of Cyphomyrus psittacus, the type species of the genus, seem to be conspecific to C. petherici. That is, the range of the genus Cyphomyrus is extended toward the Nile and Omo‐Turkana basins. This genus belongs to the large clade widely distributed in sub‐Saharian Africa and characterized by the presence of a chin appendage. Significance of this character for mormyrid phylogeny is discussed. Two distinct lineages of Pollimyrus occurring sympatrically in the White Nile tributaries and previously reported as the light and dark forms of Pollimyrus isidori together with five other congeneric species studied form a monophyletic group. The light form apparently represents P. isidori distributed in the Nile system downstream of the Murchison Falls and West Africa; the dark‐colored form (designated as Pollimyrus “D”) represents a distinct phylogenetic lineage inhabiting both the Omo‐Turkana and the White Nile basin. Morphological and ecological data suggest that this form may be conspecific to East African Pollimyrus nigricans or most probably represents a new species. [ABSTRACT FROM AUTHOR]

The molariform teeth of the mormyrid fish Hyperopisus bebe display a cone of orthodentine overlaid at their tip by a thick layer of enameloid (= acrodine). The teeth are fixed on a cellular bony tissue. This organization is classical for an actinopterygian and fits with the pattern classically observed in other osteoglossiform fishes. The presence of plicidentine and the hyoid tooth and tooth-plate morphology of this species may be related with crushing feeding habits. [ABSTRACT FROM AUTHOR]

Several studies have begun to elucidate the genetic and developmental processes underlying major vertebrate traits. Few of these traits have evolved repeatedly in vertebrates, preventing the analysis of molecularmechanisms underlying these traits comparatively. Electric organs have evolved multiple times among vertebrates, presenting a unique opportunity to understand the degree of constraint and repeatability of the evolutionary processes underlying novel vertebrate traits. As there is now a completed genome sequence representing South American electric eels, we were motivated to obtain genomic sequence from a linage that independently evolved electric organs to facilitate future comparative analyses of the evolution and development of electric organs. We report here the sequencing and de novo assembly of the genome of the mormyrid Paramormyrops kingsleyae using short-read sequencing. Inaddition,wehave completedasomatic transcriptomefrom11tissues toconstruct ageneexpressionatlasofpredicted genes fromthis assembly, enabling us to identify candidate housekeeping genes aswell as genes differentially expressed in themajor somatic tissues of the mormyrid electric fish. We anticipate that this resource will greatly facilitate comparative studies on the evolution and development of electric organs and electroreceptors. [ABSTRACT FROM AUTHOR]

This paper explores the plasticity of sexually dimorphic characters in subadult female Brevimyrus niger, an African weakly electric mormyrid species. Thirty-five fish were exposed in a staggered fashion (five fish a week) to aromatizable 17α-methyltestosterone over a period of 7 weeks; 18 fish served as untreated controls. 17α-MT induced precocious vitellogenesis that mirrored the natural maturational process during seasonal ovarian recrudescence. At the same time, 17α-MT exposure resulted in complete masculinization of the females' anal fin support structure normally observed during rainy season in adult males. We discuss possible hormonal mechanisms acting along the brain-pituitary-gonad axis that would explain the occurrence of precocious vitellogenesis and the male-typical transformation of the female's anal fin ray bases. Our findings are relevant to commercial aquaculture as the use of 17α-MT in fish hatcheries can pose serious environmental issues. [ABSTRACT FROM AUTHOR]

Many fishes perform quick and sudden swimming maneuvers known as fast-starts to escape when threatened. In pulse-type weakly electric fishes these responses are accompanied by transient increases in the rate of electric signal production known as novelty responses. While novelty responses may increase an individual's information about their surroundings, they are aerobically powered and may come at a high energetic cost when compared to fast-starts, which rely primarily on anaerobic muscle. The juxtaposition between two key aspects of fast-starts in these fishes – the aerobic novelty response and the anaerobic swimming performance – makes them an interesting model for studying effects of hypoxia on escape performance and sensory information acquisition. We acclimated the hypoxia-tolerant African mormyrid Marcusenius victoriae to either high or low dissolved oxygen (DO) levels for 8 weeks, after which fast-starts and novelty responses were quantified under both high (normoxic) and low-DO (hypoxic) test conditions. Hypoxia-acclimated fish exhibited higher maximum curvature than normoxia-acclimated fish. Displacement of normoxia-acclimated fish was not reduced under acute hypoxic test conditions. Novelty responses were given upon each startle, whether or not the fish performed a fast-start; however, novelty responses associated with fast-starts were significantly stronger than those without, suggesting a functional link between fast-start initiation and the motor control of the novelty response. Overall, hypoxia-acclimated individuals produced significantly stronger novelty responses during fast-starts. We suggest that increased novelty response strength in hypoxia-acclimated fish corresponds to an increased rate of sensory sampling, which may compensate for potential negative effects of hypoxia on higher-level processing. [ABSTRACT FROM AUTHOR]

ABSTRACT An ancient genome duplication (TGD or 3R) occurred in teleost fish after divergence from the lineage leading to gar. This genome duplication is shared by the three extant teleost lineages: Osteoglossomorpha (bony-tongues), Elopomorpha (eels and tarpons), and Clupeocephala (a large clade including salmon, carp, medaka, zebrafish, cichlids, pufferfish, stickleback, and ∼26,000 other species). After TGD, different clupeocephalan species retained different gene duplicates; this is seen clearly in Hox gene clusters but extends to all genes. Since divergent resolution of TGD paralogs is a potential driving force for speciation, it is possible this contributed to diversification of this clade. The extent to which divergent resolution of TGD paralogs occurred within Osteoglossomorpha has not been investigated in detail, and Hox cluster organization has been reported for just two species: Pantodon buchholzi (Pantodontidae) and Scleropages formosus (Osteoglossidae). We applied survey-scale genome sequencing and de novo assembly to three further osteoglossomorph taxa: Osteoglossum bicirrhosum (Osteoglossidae), Chitala ornata (Notopteridae), and Gnathonemus petersii (Mormyridae). We find that each retained more Hox genes than clupeocephalan taxa (excluding those that underwent additional genome duplication), but fewer than eels. Several Hox genes are missing in all teleosts, including duplicates of two Hox genes present in the slow evolving pre-TGD genome of the spotted gar. We find divergent resolution through individual gene losses, and whole cluster losses have been rampant across osteoglossomorphs, despite their extant species paucity. We suggest that reciprocal gene loss following TGD was probably insufficient to drive the exceptional diversification of teleosts. [ABSTRACT FROM AUTHOR]

Species of the African electric fish in the genus Paramormyrops Taverne, Thys van den Audenaerde & Heymer, 1977 constitute a recently recognized species flock with an impressive diversity of electric signals, but only modest morphological differentiation. For more than a century, confusion has surrounded the identity of Paramormyrops sphekodes (Sauvage, 1879), the earliest described species in this genus. Here we compare the morphometrics of type material to new specimens collected at the type locality on the Ogooué River of Gabon from which we additionally study DNA sequences and electric organ discharges (EODs). Based on our findings, we revise the diagnosis and description of P. sphekodes and also identify and describe a new species of Paramormyrops that is large, common and widespread in the Ogooué River basin, but cryptic and easily confounded with P. sphekodes. We designate as lectotype of P. sphekodes a specimen formerly regarded, in error, as the holotype and a second specimen originally collected with the lectotype as paralectotype. We conclude that only nine additional specimens can be identified with confidence as P. sphekodes: four from the type locality and five from a second site 45 km away. Instead of being widespread as previously thought, P. sphekodes may be restricted to a small region of the upper Ogooué River basin. Additionally, we present a revised diagnosis for the genus Paramormyrops Taverne et al., 1977, and key to species from Lower Guinea. This study illustrates the value of vouchered EOD recordings and of revisiting type localities, and lays a foundation for additional systematic work on this group. [ABSTRACT FROM AUTHOR]

Latency-dependent responses to artificial electric stimuli in 11 species of the Nilotic mormyrids were studied. In total, more than 350 poststimulus time histograms from 132 individuals were analyzed. All species studied exhibited the latency-dependent responses. Both main types of responses - phase locking and phase avoidance behavior or the preferred latency response (PLR) and preferred latency avoidance (PLA) - were found in eight species ( Brevimyrus niger, Hippopotamyrus pictus, Marcusenius cyprinoides, Mormyrus kannume, M. hasselquistii, Petrocephalus bane, P. bovei and 'Pollimyrus' petherici), while only PLR were recorded from the remaining three species ( Hyperopisus bebe, Mormyrops anguilloides and Mormyrus caschive). In eight species both types of behavior were found in fish of the same sex. In four species both types of behavior were found both in females and males. Finally, in four species both types of behavior were revealed in the same individual (in total, there were eight such individuals). In some individuals of different species the atypical responses with substantially increased latencies (compared to the typical PLR and PLA) were observed. The possible role of the phase locking and phase avoidance behavior in the mormyrid electrolocation and communication is discussed. [ABSTRACT FROM AUTHOR]

In mormyrid weakly electric fish, the electric organ discharge (EOD) is used for species recognition, orientation and prey localization. Produced in the muscle-derived adult electric organ, the EOD exhibits a wide diversity across species in both waveform and duration. While certain defining EOD characteristics can be linked to anatomical features of the electric organ, many factors underlying EOD differentiation are yet unknown. Here, we report the differential expression of 13 Kv1 voltage-gated potassium channel genes, two inwardly rectifying potassium channel genes, two previously studied sodium channel genes and an ATPase pump in two sympatric species of the genus Campylomormyrus in both the adult electric organ and skeletal muscle. Campylomormyrus compressirostris displays a basal EOD, largely unchanged during development, while C. tshokwe has an elongated, putatively derived discharge. We report an upregulation in all Kv1 genes in the electric organ of Campylomormyrus tshokwe when compared to both skeletal muscle and C. compressirostris electric organ. This pattern of upregulation in a species with a derived EOD form suggests that voltage-gated potassium channels are potentially involved in the diversification of the EOD signal among mormyrid weakly electric fish. [ABSTRACT FROM AUTHOR]

This osteological survey of 249 specimens of Brevimyrus niger ranging in size from 44 to 137 mm standard length ( LS) demonstrated that developmental changes in anal-fin morphology can serve as a predictor of sexual maturity in this species. Anal-fin ray bases begin to expand when fish reach c. 90 mm LS at which size and above there were roughly equal numbers of individuals observed with expanded and unmodified anal-fin bases, reflecting a 1:1 sex ratio. [ABSTRACT FROM AUTHOR]

Reproduction in captivity of four species of the mormyrid genus Campylomormyrus was investigated. Cyclical reproduction was provoked by changing water conductivity (C) alone: decreasing C led to gonadal recrudescence, an increase induced gonad regression. Data on the reproduction and development of three species are presented. All three species are indeterminate fractional spawners. Spawning intervals ranged from 6 to 66 days in C. rhynchophorus, 10-75 days in C. tshokwe, and 18 days in C. compressirostris (calculated values). Fecundities (eggs per fractional spawning) ranged from 70 to 1570 eggs in C. rhynchophorus, 100-1192 in C. tshokwe, and 38-246 in C. compressirostris. Spawnings/ovipositions occurred during the second half of the night; no parental care was observed; no special spawning substrates were necessary. C. compressirostris successfully spawned in breeding groups, C. rhynchophorus as pair. Agonistic behavior in the C. tshokwe pair forced us to divide the breeding tank; therefore, only ovipositions occurred. However, injection of an artificial GnRH hormone allowed us to obtain ripe eggs and sperm and to perform successful artificial reproduction. All three species produce yolky, slightly sticky eggs. Egg diameter ranges from 2.3-3.0 mm. Hatching occurred on day 3, feeding started on day 11. Transition from larval to juvenile stage occurred at around 20 mm total length (TL). At this size C. rhynchophorus developed a higher body than the two other species and differences between the species in the melanin pigmentation of the unpaired fins occurred. Between 32 and 35 mm TL the upper and lower jaws started to elongate. [ABSTRACT FROM AUTHOR]

Recently, we reported evidence for a novel mechanism of peripheral sensory coding based on oscillatory synchrony. Spontaneously oscillating electroreceptors in weakly electric fish (Mormyridae) respond to electrosensory stimuli with a phase reset that results in transient synchrony across the receptor population (Baker et al., 2015). Here, we asked whether the central electrosensory system actually detects the occurrence of synchronous oscillations among receptors. We found that electrosensory stimulation elicited evoked potentials in the midbrain exterolateral nucleus at a short latency following receptor synchronization. Frequency tuning in the midbrain resembled peripheral frequency tuning, which matches the intrinsic oscillation frequencies of the receptors. These frequencies are lower than those in individual conspecific signals, and instead match those found in collective signals produced by groups of conspecifics. Our results provide further support for a novel mechanism for sensory coding based on the detection of oscillatory synchrony among peripheral receptors.

L’étude de la parasitofaune branchiale d’un Mormyridae, Mormyrus rume Valenciennes, 1846 (Teleostei : Mormyridae), capturé dans le lac de retenue d’Ayamé I en Côte d’Ivoire (Afrique de l’Ouest) a révélé la présence de trois Monogènes nouveaux du genre Bouixella Euzet & Dossou, 1976, qui se différencient des autres espèces du genre par la taille et la morphologie des pièces haptoriales (anchor dorsal et ventral, barre dorsale et ventrale) et de l’appareil génital mâle. Nous décrivons dans ce travail ces trois nouvelles espèces : Bouixella gorei n. sp., Bouixella yaoi n. sp. et Bouixella koutouani n. sp.

Alarge brain can offer several cognitive advantages. However, brain tissue has an especially high metabolic rate. Thus, evolving an enlarged brain requires either a decrease in other energetic requirements, or an increase in overall energy consumption. Previous studies have found conflicting evidence for these hypotheses, leaving the metabolic costs and constraints in the evolution of increased encephalization unclear. Mormyrid electric fishes have extreme encephalization comparable to that of primates. Here, we show that brain size varies widely among mormyrid species, and that there is little evidence for a trade-off with organ size, but instead a correlation between brain size and resting oxygen consumption rate. Additionally, we show that increased brain size correlates with decreased hypoxia tolerance. Our data thus provide a non-mammalian example of extreme encephalization that is accommodated by an increase in overall energy consumption. Previous studies have found energetic trade-offs with variation in brain size in taxa that have not experienced extreme encephalization comparable with that of primates and mormyrids. Therefore, we suggest that energetic trade-offs can only explain the evolution of moderate increases in brain size, and that the energetic requirements of extreme encephalization may necessitate increased overall energy investment. [ABSTRACT FROM AUTHOR]

Karyotyping is a basic method to investigate chromosomal evolution and genomic rearrangements. Sixteen genera within the basal teleost order Osteoglossiformes are currently described cytogenetically. Our study adds information to this chromosomal dataset by determining the karyotype of Campylomormyrus compressirostris , a genus of African weakly electric fish that has not been previously examined. Our results indicate a diploid chromosome number of 2n = 48 (4sm + 26m + 18a) with a fundamental number of FN = 72. This chromosome number is identical to the number documented for the sister taxon of the genus Campylomormyrus , i.e. , Gnathonemus petersii (2n = 48). These results support the close relationship of Campylomormyrus and Gnathonemus . However, the karyotype formula of C. compressirostris is different from Gnathonemus petersii , thereby confirming the high variability of karyotype formulae within the Mormyridae. We infer that the differences in chromosome number and formula of Campylomormyrus relative to other mormyrids may be caused by Robertsonian fusion and pericentric inversion. In addition to the karyotype description and classification of Campylomormyrus , a ChromEvol analysis was used to determine the ancestral haploid chromosome number of osteoglossiform taxa. Our results indicate a relatively conservative haploid chromosome number of n = 24 for the most recent common ancestor of Osteoglossiformes and for most of the internal nodes of osteoglossiform phylogeny. Hence, we presume that the high chromosome variability evolved recently on multiple independent occasions. Furthermore, we suggest that the most likely ancestral chromosome number of Mormyridae is either n = 24 or n = 25. To the best of our knowledge this is the first attempt to determine and classify the karyotype of the weakly electric fish genus Campylomormyrus and to analyze chromosomal evolution within the Osteoglossiformes based on Maximum Likelihood and Bayesian Inference analyses. [ABSTRACT FROM AUTHOR]

The anatomical organization of African Mormyrids’ brain is a clear example of departure from the average brain morphotype in teleosts, probably related to functional specialization associated to electrosensory processing and sensory-motor coordination. The brain of Mormyrids is characterized by a well-developed rhombencephalic electrosensory lobe interconnected with relatively large mesencephalic torus semicircularis and optic tectum, and a huge and complex cerebellum. This unique morphology might imply cell addition from extraventricular proliferation zones up to late developmental stages. Here we studied the ontogeny of these brain regions in Mormyrus rume proboscirostris from embryonic to adult stages by classical histological techniques and 3D reconstruction, and analyzed the spatial-temporal distribution of proliferating cells, using pulse type BrdU labeling. Brain morphogenesis and maturation progressed in rostral-caudal direction, from 4 day old free embryos, through larvae, to juveniles whose brain almost attained adult morphological complexity. The change in the relative size of the telencephalon, and mesencephalic and rhombencephalic brain regions suggest a developmental shift in the relative importance of visual and electrosensory modalities. In free embryos, proliferating cells densely populated the lining of the ventricular system. During development, ventricular proliferating cells decreased in density and extension of distribution, constituting ventricular proliferation zones. The first recognizable one was found at the optic tectum of free embryos. Several extraventricular proliferation zones were found in the cerebellar divisions of larvae, persisting along life. Adult M. rume proboscirostris showed scarce ventricular but profuse cerebellar proliferation zones, particularly at the subpial layer of the valvula cerebelli, similar to lagomorphs. This might indicate that adult cerebellar proliferation is a conserved vertebrate feature. [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]

Voltage-gated sodium channels, Nav1, play a crucial role in the generation and propagation of action potentials and substantially contribute to the shape of their rising phase. The electric organ discharge (EOD) of African weakly electric fish (Mormyroidea) is the sum of action potentials fired from all electrocytes of the electric organ at the same time and hence voltage-gated sodium channels are one factor-together with the electrocyte's morphology and innervation pattern-that determines the properties of these EODs. Due to the fish-specific genome duplication, teleost fish possess eight copies of sodium channel genes (SCN), which encode for Nav1 channels. In mormyroids, SCN4aa is solely expressed in the electrocytes of the adult electric organ. In this study, we compared entire SCN4aa sequences of six species of the genus Campylomormyrus and identified nonsynonymous substitutions among them. SCN4aa in Campylomormyrus exhibits a much higher evolutionary rate compared to its paralog SCN4ab, whose expression is not restricted to the electric organ. We also found evidence for strong positive selection on the SCN4aa gene within Mormyridae and along the lineage ancestral to the Mormyridae. We have identified sites at which all nonelectric teleosts are monomorphic in their amino acid, but mormyrids have different amino acids. Our findings confirm the crucial role of SCN4aa in EOD evolution among mormyrid weakly electric fish. The inferred positive selection within Mormyridae makes this gene a prime candidate for further investigation of the divergent evolution of pulse-type EODs among closely related species. [ABSTRACT FROM AUTHOR]

African weakly-electric fishes (Mormyridae) are able to communicate through species-specific electric signals; this feature might have favoured the evolutionary radiation observed in this family (over 200 species) by acting as an effective pre-zygotic isolation mechanism. In the present study we used mitochondrial ( cytb ) and nuclear ( rps7 , scn4aa ) markers in order to reconstruct a species-phylogeny and identify species boundaries for the genus Campylomormyrus , by applying inference methods based on the multispecies coalescent model. Additionally, we employed 16 microsatellite markers, landmark-based morphometric measurements, and electro-physiological analyses as independent lines of evidence to the results obtained from the sequence data. The results show that groups that are morphologically different are also significantly divergent at the genetic level, whereas morphologically similar groups, displaying dissimilar electric signals, do not show enough genetic diversity to be considered separate species. Furthermore, the data confirm the presence of a yet undescribed species within the genus Campylomormyrus . [ABSTRACT FROM AUTHOR]

Recently, we reported evidence for a novel mechanism of peripheral sensory coding based on oscillatory synchrony. Spontaneously oscillating electroreceptors in weakly electric fish (Mormyridae) respond to electrosensory stimuli with a phase reset that results in transient synchrony across the receptor population (Baker et al., 2015). Here, we asked whether the central electrosensory system actually detects the occurrence of synchronous oscillations among receptors. We found that electrosensory stimulation elicited evoked potentials in the midbrain exterolateral nucleus at a short latency following receptor synchronization. Frequency tuning in the midbrain resembled peripheral frequency tuning, which matches the intrinsic oscillation frequencies of the receptors. These frequencies are lower than those in individual conspecific signals, and instead match those found in collective signals produced by groups of conspecifics. Our results provide further support for a novel mechanism for sensory coding based on the detection of oscillatory synchrony among peripheral receptors. [ABSTRACT FROM AUTHOR]

We critically comparedMarcuseniusspecimens from the mouth of the Cunene River on the Namibia/Angola border, a harsh desert environment on the Atlantic Ocean coast virtually devoid of aerial insects with aquatic larvae which are an important food item, withMarcusenius multisquamatusKramer & Wink, 2013 from the escarpment region of that same river, in a relatively rich and productive subtropical savannah environment. River mouth specimens were differentiated in morphology and electric organ discharges, as determined by ANOVA/MANOVA comparisons, principal component and discriminant analyses on morphological and electrophysiological characters, and genetics, including sequences of the mitochondrial cytochromebgene, indicating reproductive isolation. Specimens from the river mouth differed fromM. multisquamatus, their closest relatives, by having a shorter snout, a smaller eye diameter, and smaller nares separation. River mouth specimens were also differentiated from other, increasingly less-close relatives, such asM. altisambesiKramer et al., 2007 from the Okavango River, Botswana, and fromM. krameriMaake et al., 2014 from the Limpopo System, South Africa. We therefore designate the new speciesMarcusenius desertussp. nov. for the Cunene River mouth population. [ABSTRACT FROM PUBLISHER]

We use mitochondrial and nuclear sequence data to show that three weakly electric mormyrid fish specimens collected at three widely separated localities in Gabon, Africa over a 13-year period represent an unrecognized lineage within the subfamily Mormyrinae and determine its phylogenetic position with respect to other taxa. We describe these three specimens as a new genus containing two new species. Cryptomyrus, new genus, is readily distinguished from all other mormyrid genera by a combination of features of squamation, morphometrics, and dental attributes. Cryptomyrus ogoouensis, new species, is differentiated from its single congener, Cryptomyrus ona, new species, by the possession of an anal-fin origin located well in advance of the dorsal fin, a narrow caudal peduncle and caudal-fin lobes nearly as long as the peduncle. In C. ona, the anal-fin origin is located only slightly in advance of the dorsal fin, the caudal peduncle is deep and the caudal-fin lobes considerably shorter than the peduncle. Continued discovery of new taxa within the "Lower Guinea Clade" of Mormyridae highlights the incompleteness of our knowledge of fish diversity in West-Central Africa. We present a revised key to the mormyrid genera of Lower Guinea. [ABSTRACT FROM AUTHOR]