Petrocephalus christyi

Petrocephalus christyi Boulenger, 1920

Original Published Description:

Boulenger, G. A. (1920).  Poissons recueillis au Congo Belge par l'expédition de Dr C. Christy. Annales du Musée du Congo belge. Zoologie. Série I, Matériaux pour la faune du Congo. 2, 38.
 
Languages: English

Overview

General Description

From Boulenger 1920,  p.11 Hauteur du corps 3 à 3 1/3 fois dans la longueur totale, longueur de la tête 3 ½ à 4 fois. Tête longue comme haute, ou un peu plus longue que haute; museau très court, à profil arrondi, mesurant les 2/3 du diamètre de l'œil, qui est compris 3 1/3 à 3 2/3 fois dans la longueur de la tête et égale la largeur interoculaire; bouche sous le centre de l'œil, sa largeur 1/5 à 1/4 de la longueur de la tête; dents bicuspides, 10 à 12 à la mâchoire supérieure, 20 à 22 à l'inférieure. Dorsale 25-27, commençant au-dessus ou un peu en arrière de l'origine de l'anale; la longueur de sa base 1 2/5 à 1 3/5 fois dans la distance qui la sépare de la tête et à peu près égale à sa distance de la caudale. Anale 26-29, à égale distance de la base de la ventrale et de la caudale. Pectorale pointue, un peu plus courte que la tête, s'étendant bien au delà de la base de la ventrale. Caudale à lobes pointus, écailleuse à la base. Pédicule caudal 3 fois aussi long que haut, mesurant les 2/3 ou les 3/4 de la longueur de la tête. 39 ou 40 écailles le long  de la ligne latérale 8-10/10-12 en série transversa1e sur le corps, 10-12/10-12 entre la dorsale et l'anale, 12 autour du pédoncule caudal. Coloration argentée, le dos brun foncé; une tache arrondie noirâtre sous les premiers rayons de la dorsale, qui sont également noirâtres; une bande noirâtre en forme de croissant à la base de la caudale. Longueur totale 110 millimètres.

 

Description expanded in Lavoué et al (2010) as: Petrocephalus christyi is a medium–sized species within the genus (maximum standard length observed = 100.0 mm). Body ovoid, body 2.7-3.2 longer than high (syntypes = 3.0–3.2) and laterally compressed. Head length between 3.2 and 3.7 times in standard length (syntypes = 3.5–3.7). Snout of intermediate size and round. Eye large (3.1 ≤ Head length/eye diameter ≤ 3.8, syntypes = 3.1–3.8). Mouth small (4.1 ≤ Head length/Head width ≤ 5.5, syntypes = 4.7–5.5), sub–terminal, opening just under the anterior half of the eye. Teeth small and bicuspid, 9–10 in a single row in the upper jaw, 19–21 in the lower jaw. Dorsal and anal fins originate in the posterior half of the body, with pre–dorsal distance equal to pre–anal distance. Dorsal fin with 22–24 branched rays (syntypes = 23–24). Anal fin with 25–27 branched rays (syntypes = 26–27). Scales cover the body, except for the head. Lateral line visible and complete with 35–39 (syntypes = 35–39) pored scales along its length. Thirteen to 15 scales (syntypes = 13–14) between the anterior base of the anal fin and the lateral line. Caudal peduncle relatively thin (2.5 ≤ CPL/CPD ≤ 3.0, syntypes = 2.5–3.0). Twelve scales around the caudal peduncle. Skin on head thick, turning opaque with formalin fixation, with numerous electroreceptors organized into three distinct rosettes. However, the Augenrosette (above the eye) is not as developed as it is in the other species of Petrocephalus exhibiting this rosette.

Body uniformly white–silver, with the presence of two characteristic melanin marks: (1) a distinct round mark below the anterior base (first to fifth rays) of the dorsal fin; (2) a rather diffuse crescent–like mark, centered at the base of the caudal fin and extending onto the upper and lower fleshy lobes of this fin. The fins themselves are translucent. 

Description

Diagnostic Description

Petrocephalus christyi is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin with 22–24 branched rays. Anal fin with 25–29 branched rays. Eye large (Head length/eye diameter ≤ 4.2, range = 3.1–4.2). Mouth small (2.9 ≤ Head length /mouth width, range = 2.9–5.5). Nine to 13 teeth in the upper jaw, 17–22 teeth in the lower jaw. Melanin patterning consisting of two characteristic black patches: (1) a distinct round mark below the anterior base (first to the fifth rays) of the dorsal fin; (2) a somewhat diffuse crescent–like mark, centered at the base of the caudal fin and extending onto the fleshy dorsal and ventral lobes of this fin.

In the small number of individuals recorded so far, the EOD is of normal polarity, four–phasic, with a relatively slow initial rise.

Author(s): Lavoué, Sébastien
Rights holder(s): Lavoué, Sébastien

Electric Organ Discharge

EOD of this species does appear to be distinctive. The EOD exhibits normal polarity and is four–phasic with a large, negative–going P2 and smaller peaks, P1, P3 and P4. Similar to the EODs of the Odzala population of P. microphthalmus, a relatively long, slow rise occurs during the initial part of the first head–positive phase in the EODs of both individuals of P. christyi. This rise toward P1 has a shoulder-like inflection point, which at magnified gain is seen to possess a small, negative-going local peak. Both the slow rise and inflection point are subtle features of the EOD; they are only visible in amplified traces. Unlike the EODs of P. microphthalmus, however, those of the two P. christyi individuals possess a prominent head–negative fourth peak (P4), the amplitude of which is 4.5 – 8.6 % of the waveform’s total peak–to–peak swing. A prominent P4 is also present in the EOD emitted by the only individual of Petrocephalus mbossou ever recorded, but otherwise a P4 seems to be rare in Petrocephalus. Based on 1.5% voltage deviations from baseline relative to peak-peak amplitude and at ambient recording temperatures, duration of the EOD is between 0.284 and 0.390 msec in P. christyi, falling in the range of many other Petrocephalus species. Electrocyte anatomy is presumed to be of type NPp based on the EOD waveform, but this has not yet been confirmed histologically.

Author(s): Lavoué, Sébastien
Rights holder(s): Lavoué, Sébastien

Size

To 100.0 mm SL

Author(s): Lavoué, Sébastien
Rights holder(s): Lavoué, Sébastien

Look Alikes

As currently recognized, probably a species complex.

Author(s): Lavoué, Sébastien
Rights holder(s): Lavoué, Sébastien

Ecology and Distribution

Distribution

Endemic to the Congo River basin. The type specimens were collected at the locality Bosabangui along the Lindi River. Petrocephalus christyi is known from several localities in the Congo basin: Odzala, Pool Malebo (Lower Congo), Yangambi region, etc.

Author(s): Lavoué, Sébastien
Rights holder(s): Lavoué, Sébastien

Evolution and Systematics

Phylogenetic Relationships

Petrocephalus christyi is the sister group of P. mbossou nested within a large clade of mostly Central Africa endemic species.

Author(s): Lavoué, Sébastien
Rights holder(s): Lavoué, Sébastien

References

Boulenger, G. A. (1920).  Poissons recueillis au Congo Belge par l'expédition de Dr C. Christy. Annales du Musée du Congo belge. Zoologie. Série I, Matériaux pour la faune du Congo. 2, 38.
 
David, L., & Poll M. (1937).  Contribution à la faune ichthyologique du Congo Belge: Collections du Dr. H. Schouteden (1924-1926) et d'autres récolteurs. Annales du Musée du Congo Belge (Série 1). 3 (fasc. 5), 189–294.
 
Harder, W. (2000).  The Mormyridae and other Osteoglossomorpha (CD-ROM). World Biodiversity Database, CD-ROM Series. 2000, New York: Springer Verlag, ETI-UNESCO.
Hopkins, C. D., Lavoué S., & Sullivan J. P. (2007).  12. Mormyridae. (StiassnyM L J., TeugelsG G., HopkinsC D., Ed.).The Fresh and Brackish Water Fishes of Lower Guinea, West-Central Africa. 1, 220–334.
 
Lavoué, S., Arnegard M. E., Sullivan J. P., & Hopkins C. D. (2008).  Petrocephalus of Odzala offer insights into evolutionary patterns of signal diversification in the Mormyridae, a family of weakly electrogenic fishes from Africa. Journal of Physiology-Paris. 102, 322-339. Abstract
 
Lavoué, S., Sullivan J. P., & Arnegard M. E. (2010).  African weakly electric fishes of the genus Petrocephalus (Osteoglossomorpha: Mormyridae) of Odzala National Park, Republic of Congo (Lékoli River, Congo River basin) with description of five new species. Zootaxa. 2600, 1-52.
 
Poll, M. (1967).  Contribution à la Faune Ichthyologique de l'Angola. Publicações Culturais. 381. Lisbon: Companhia de Diamantes de Angola.
 
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Boulenger1920_Poissons recuellis au Congo Belge.pdf4057.52010-11-10T20:23:13Z
Lavoué et al 2010.pdf4462.32010-11-19T21:53:21Z
Hopkins, Lavoué, Sullivan 2007.pdf932.92010-11-27T21:38:42Z
Poll_1967_optimized.pdf4223.82010-12-06T21:13:01Z
david_poll_1937.pdf857.12014-03-18T20:15:15Z
lavoue_et_al_2008d.pdf2492.52011-02-28T05:43:08Z