Gnathonemus Petersi Research Articles

Spectral sensitivity of the weakly discharging electric fish Gnathonemus petersi using its electric organ discharges as the response measure

The spectral sensitivity of the weakly electric mormyrid fish Gnathonemus petersi was investigated under dark‐ and light‐adapted conditions using a transient change (startle) in its electric organ discharge (EOD) rate as response measure. The startle was resistant to habituation and graded with light intensity. Under both lighting conditions, the fish responded optimally to a monochromatic light of 525 nm. A porphyropsin pigment (520–5402) appears to mediate spectral sensitivity over most of the visible spectrum. However, G. petersi responded more strongly to 625‐ and 675‐nm lights (dark‐ and light‐adapted fish) and a 725‐nm light (light‐adapted fish only) than predicted by the presence of a single rod pigment. These data suggest that at least one additional visual pigment (most likely of cone cells) maximally absorbing long wavelength light (600 nm or longer) is present. The spectral sensitivity data are consistent with the sensitivity hypothesis in that heightened sensitivity to long wavelength light is predicted for fish living in blackwater habitats which are characterized typically by low light levels and transmission of predominantly long wavelengths. Histology of the retina showed photoreceptors grouped into bundles and ensheathed by pigment epithelial cells. Our results demonstrated a functional visual sense in a species of fish much better known and studied for its electrosensory and electromotor abilities.

Responses of electric fish (family mormyridae) to inorganic nutrients and triubinryltin oxide

A microcomputer-based fish monitor has been used to evaluate the effect of selected inorganic nutrients and Tributyltin Oxide (TBTO) on the electric organ discharge (EOD) of two species of elephant fish, namely Gnathonemus petersi and G. tamandua (family: Mormyridae). Significant EOD responses to dosing concentrations as low as 1.0mg/l ammonia (NH 4-N), 0.05mg/l phosphate (PO 4-P) and 0.01mg/l TBTO are recorded by both species, with response times within a 15–45 minute range. No response, however, was recorded to concentrations within a range of 10–75mg/l Nitrate (NO 3-N). This should reduce the instance of `false alarms' for which such systems are renowned. These findings add further credibility to the potential of these fish for use as indicators of chemical changes in water quality.

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

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

Responses of electric fish (Family Mormyridae) to chemical changes in water quality: II. Pesticides

Abstract Two species of weakly electric fish, Gnathonemus petersi and G. tamandua (Family Mormyridae), have been exposed to differing concentrations of atrazine, atrazine in the presence of cyanide and lindane. Significant responses to concentrations of 0.1 mgl‐1 and 0.05 mgl‐1 of both compounds were measured as modification of the electric organ discharge (EOD) rate. Applications of 0.05 mgl‐1 atrazine plus 0.1 mgl‐1 cyanide have a synergistic effect on sensitivity of response.

Responses of electric fish (family mormymdae) to chemical changes in water quality: I. cyanide

Abstract The effect of cyanide on the electric organ activity of two species of the tropical monnyrid fish, Gnathonemus petersi and Gnathonemus tamanduá have been examined. Significant responses in the mean electric organ discharge rate (EOD) are measured following the introduction of cyanide at a concentration of 25μg l−1. This corresponds with an increase in the variance. There is also a significant response detected at a concentration of 5μg l−1 but in this case the time to react is increased.

Treatment of fish parasites 8. Effects of sym. triazinone (Toltrazuril) on developmental stages of Henneguya sp. (Myxosporea, Myxozoa): A Light and Electron Microscopic Study

Summary In research of chemotherapy of fish parasitized by myxosporeans toltrazuril was tested in vivo against Henneguya sp. parasitizing the primary gill filaments in the tapir fish, Gnathonemus petersi. Naturally infected tapir fish were incubated at 22° C in water containing 0, 5, 10, or 20 µg toltrazuril/ml, or the pure solvent for 4 or 2 h, respectively. It was found that the drug caused severe damages in all developmental stages of Henneguya sp. except the mature spores. Starting with a dose of 5 µg/ml and 4 h exposure, a destruction of the mitochondria and a decrease in the number of ribosomes was observed in the uni- and multicellular stages. After treatment with 10 µg/ml, in the unicellular stages the karyoplasms were partially lyzed. In pansporoblasts with differentiated sporoplasm and beginning differentiation of the polar filament all organelles in the cytoplasm of the valvulogenic cells were destroyed after incubation in 10 µg toltrazuril/ml. In all cells the perinuclear space was enlarged. The grade of damage increased after incubation in 20 µg toltrazuril/ml for 2 h. In capsulogenic cells, in which the polar capsule formation had already started, their rough endoplasmic reticulum was dilated. In premature pansporoblasts when valve production has started, a shrinking of the sporoplasm and of the capsulogenic cells was only observed after treatment with the highest dose (20 µg/ml; 2 h) : in some cases the pansporoblasts burst. The pure solvent had no effects on developmental stages of Henneguya sp. From these results it is suggested that chemotherapy against Henneguya sp. should be accomplished by bathing the fish in aerated containers with 10 µg toltrazuril/l for 4 h. This treatment will decrease considerably the output of spores. However, since the mature spores are not affected, the treatment has to be repeated within several months. Fish with extensive skin lesions, caused by net-catching to infections by fungi, should be treated under careful observation, because these factors decrease the tolerance of the drug.

Microcomputer‐based monitoring of the effect of phenol on electric organ activity in the mormyrid fishgnathonemus petersi

Abstract A microcomputer‐based monitoring system has been used to evaluate the effect of phenol solution on the electric organ discharges (EOD) of the elephant; fish Gnathonemus petersi (family: Mormyridae). Prior to experimentation, fish‐ are acclimatised for at least 48 h at 25°c. Using absolute calculations of phenol in the range 0–6 mgl−1, significant increases in the mean and variance of EOD, measured as pulses per min (PPM), are recorded with levels as low as 1 mgl”; within 30–90 min of dosing. At higher levels of 4–6 mgl−1, the increases in EOD are occasionally followed by a decrease during the period of dosing.

Microcomputer‐based detection and analysis of the electric organ discharges in the mormyrid fishgnathonemus petersi

Abstract A microcomputer‐based monitoring system has been developed to study the electrical organ discharges (EOD) of the elephant fish Gnathonemus petersi (family: Mormyridae). The system can monitor up to 4 individual fish, whilst simultaneously performing graphical and comparative statistical analysis of the incoming data, expressed as pulses per minute (PPM). Normal EOD or stable patterns are quickly obtained if the elephant fish are maintained at 25°C for at least 48 h in laboratory aquaria tanks. Feeding and movements visible to the fish are among other factors which upset background EOD distributions.

Afferent and efferent connections of cerebellar lobe C3 of the mormyrid fish Gnathonemus petersi: an HRP study.

The present paper is devoted to the extrinsic connections of lobe C3 of the highly differentiated corpus cerebelli of the electric fish Gnathonemus petersi. For this purpose, HRP injections or gels were placed in distinct parts of lobe C3 or its peduncle, in the pretectal region, and in the eye. Moreover, the presence of serotonin and tyrosine-hydroxylase was studied with immunohistochemical methods. The afferent connections of the rostral and caudal part of lobe C3 appear to differ considerably. Although both parts receive comparable projections from two pretectal nuclei (termed nucleus geniculatus and dorsal anterior pretectal nucleus) and the inferior olive, they receive projections from different parts of the nucleus lateralis valvulae, a large cell mass in the midbrain tegmentum, composed of small, tightly packed neurons. The caudal part of lobe C3 receives a projection from the most rostromedial cap of cells of this nucleus, whereas the rostral cap of lobe C3 receives efferents from the neighboring, more caudolateral, zone of cells of the nucleus lateralis valvulae. The caudal part of lobe C3, but not its rostral part, receives an additional projection from a nucleus in the isthmus region, termed nucleus Q. This nucleus sends a collateral projection to the torus longitudinalis. The efferents of both parts of lobe C3 project to slightly different parts of the midbrain tegmentum and the nucleus reticularis superior, and originate at least partly from eurydendroid cells. None of the nuclei and fiber tracts labeled could be shown to contain serotonin or catecholamines. The connections of lobe C3, as revealed by the present study, are compared with those of other parts of the mormyrid cerebellum and with those of the corpus cerebelli of other teleosts, with emphasis on the homology and functional significance of pretectocerebellar connections, the topical order in the cerebellar projections of the nucleus lateralis valvulae, and the relations between the cerebellum and torus longitudinalis. Comparison of the cerebellar connections in different teleostean species suggests that the strong development and the considerable differentiation of the cerebellum of mormyrids are related to at least two types of changes in the extrinsic connections, i.e.: a redistribution or parcelling of connections and the development of connections specific for mormyrids.

Afferent and efferent connections of cerebellar lobe C1 of the mormyrid fish Gnathonemus petersi: an HRP study.

The corpus of the highly developed cerebellum of the weakly electric fish Gnathonemus petersi is differentiated into four lobes, numbered C1 to C4. The present paper deals with the extrinsic connections of the rostralmost lobe C1. Relevant nuclei were studied in normal histological material and HRP injections were placed in lobe C1, the neighbouring pedunculus valvulae, and the brainstem. The largest number of afferents to lobe C1 originates from the nucleus lateralis valvulae, a large nucleus of tightly packed small cells in the dorsal midbrain tegmentum. In Gnathonemus this nucleus encompasses nine subdivisions, of which the rostral, caudal, and exterolateral parts project in particular to lobe C1. Larger neurons in the dorsal midbrain tegmentum and presumed mesencephalic trigeminal neurons project to C1 as well. In the rhombencephalon, afferents to lobe C1 arise from the first funicular nucleus, the lateral reticular nucleus, and the inferior olive. Efferents of lobe C1 have been found to arise from a peculiar cell type in the Purkinje cell layer (so-called eurydendroid neurons) and to project predominantly to the nucleus of the fasciculus longitudinalis medialis, the nucleus reticularis superius and medius, and the trigeminal motor nucleus. Additional small projections terminate in the tectum mesencephali and in the nucleus reticularis inferior. Compared with other parts of the mormyrid cerebellum as well as with the cerebellum of other teleosts, the connections of lobe C1 appear to be quite restricted and specialized. In this respect the connections with the trigeminal nerve via the first funicular nucleus, the mesencephalic trigeminal nucleus, and the trigeminal motor nucleus are of particular interest. The absence of central cerebellar nuclei intercalated in the efferent cerebellar connections, in combination with the presence of a precerebellar nucleus (lateralis valvulae) involved in the afferent cerebellar connections, represents a remarkable difference between teleosts and other vertebrate classes.

A toxicity warning monitor using the weakly electric fish, Gnathonemus petersi

A technically simple fish monitor was developed using the weakly electric fish, Gnathonemus petersi, as the test organism. The test system consists of a plexiglass test chamber (21., 27°C) with a flow-through of 4–5 times the chamber volume per hour. The spontaneous electric organ discharges (EOD) are recorded as activity signals. EODs, which have a potential of about 500 mV, last 0.3 ms and they can be converted to computer-compatible signals by a simple amplifier. The EOD-activity is analyzed by a low-cost desk-top computer. Two different modes of analysis which represent two levels of response sensitivity, are possible either alternatively or simultaneously. The toxicity response of Gnathonemus petersi was measured in experiments with the toxicants Hg 2+, Cu 2+, NaAsO 2 and CN −. The sensitivity to acutely toxic concentrations was found to be as high as that of trout or minnows.

Influence of electrical stimulation and deprivation on the electric organ discharge behaviour and metabolism of neuronal gangliosides of the tapirfish ( Gnathonemus petersi, Mormyridae, Teleostei)

1. 1. The influence of electrical stimulation (“attack”-frequency of 40 Hz, 2 V, 2 days) and of social and electrical deprivation on the metabolism of gangliosides of various brain structures and the electric organ of the weakly electric tapirfish ( Gnathonemus petersi, Mormyridae) was investigated. 2. 2. After stimulation the daily average discharges of the electric organ increased from 9.4 to 11.1 Hz, whereas after deprivation they decreased to 7.9 Hz as compared with controls. 3. 3. There were significant and structure specific differences in some ganglioside-fractions (G M1, G D3, G D1a, G D1b, and G P1) in concentration and in specific radioactive NeuAc-labelling between stimulated and deprived animals respectively, compared with controls.

Size and Allometry of the Saccular Air Bladder of Gnathonemus petersi (Pisces: Mormyridae): Implications for Hearing

Size and Allometry of the Saccular Air Bladder of Gnathonemus petersi (Pisces: Mormyridae): Implications for Hearing

Studies on Monogenetic Trematodes. XXXIX. Exotic Species of Monopisthocotylea with the Proposal of Archidiplectanum gen. n. and Longihaptor gen. n.

The family Diplectanidae Bychowsky, 1957, and the genera Ancylodiscoides Yamaguti, 1937, Heteroncocleidus Bychowsky, 1957, and Trianchoratus Price and Berry, 1966, are emended. Archidiplectanum gen. n. and Longihaptor gen. n. are proposed and the following new species are described: Ancylodiscoides caecus from an unidentified fish (USNM No. 202610), Thailand; Archidiplectanum archidiplectanum from Gnathonemus petersi (Gunther), western Africa; Heteroncocleidus gracilis from Colisa labiosa (Day), India; Longihaptor longihaptor from Cichla ocellaris Bloch and Schneider, Brazil; Urocleidoides amazonensis and U. catus (both) from Phractocephalus hemiliopterus (Bloch and Schneider), Brazil; U. megorchis from Sorubim lima (Bloch and Schneider), La Plata Drainage to the Magdalena, S. A.; U. robustus from an unidentified South American catfish; and U. variabilils from Symphysodon discus Heckel, Brazil. Trianchoratus acleithrium Price and Berry, 1966, is redescribed. Conspicuous survival of immediately ancestral and liaison species of some Monopisthocotylea is suggested by present information, part of which is contributed by this investigation. Such information implies that the barriers between different genera, subfamilies, and even families are becoming less formidable and in some cases apparently are disappearing. It is postulated that when a comprehensive number of monopisthocotylean species are described, genera and higher taxa may insensibly intergrade with cne another as segments in a continuous succession of species that differ radically only at remotely separated points. On a generic level this phenomenon is illustrated in the Ancyrocephalinae by the originally disjunct genera Cleidodiscus Mueller, 1934 (Mizelle and Hughes, 1938), Urocleidoides Mizelle and Price, 1964 (Mizelle, Kritsky and Crane, 1968), and Urocleidus Mueller, 1934 (Mizelle and Hughes, 1938). Cleidodiscus and Urocleidus, being typically Nearctic genera, occur on fishes very different from those in the Neotropical Region that harbor species of Urocleidoides. The genus Cleidodiscus is characterized by a sinistral vagina (when present) and a proximally articulated cirrus and accessory piece. Urocleidoides is distinguished principally by a sinistral or ventral vagina (when present) and usually a proximally nonarticulated cirrus (coiled shaft) and accessory piece. Principal characteristics of Urocleidus are a 1 Present address: Department of Zoology, University of Illinois, Urbana

A latency-change mechanism involved in sensory coding of electric fish (mormyrids)

Mormyrids, African weakly electric fish, display a low frequency electric discharge generated by the caudally located electric organ between the anal, dorsal and caudal fins. Each electric pulse has a diphasic form and a duration of 0.5 msec. The properties of sensory impulses recorded in single lateral line fibers of Gnathonemus petersi and stanleyanus were studied. Many fibers in the dorsal branch of the lateral line nerve responded with 1–2 or several (up to five) impulses to each electric organ pulse. Regardless of the number of sensory impulses, a shortening or lengthening of their latency with respect to the electric organ pulse (latency change) was observed, when a conductive (silverplate) or non-conductive (plastic plate) object was placed at the level of the receptor. The range of the latency change appeared to be larger (7–8 msec) in fibers which displayed a maximal discharge of one or two impulses than in those which at maximum displayed several impulses. In the latter, a variation of latency occurs along with a change in number of impulses. Conductive and non-conductive objects have opposite effects. An imposed electric current pulse in the water elicited fiber responses similar to those evoked by the electric organs pulse. Increasing pulse strength produced a smooth latency shortening of sensory impulses.