Petrocephalus odzalaensis

Petrocephalus odzalaensis Lavoué, Sullivan & Arnegard, 2010

Languages: English

Overview

General Description

Petrocephalus odzalaensis is a medium sized species within the genus (maximum standard length observed = 99.3 mm; holotype = 92.9 mm). Body ovoid, body 2.6-2.9 longer than high (holotype = 2.6) and laterally compressed. Head length between 3.7 and 4.0 times in standard length (average = 3.9, holotype = 4.0). Snout short and round. Mouth small (4.0 ≤ Head length/mouth width ≤ 4.8, average = 4.3, holotype = 4.3), sub–terminal, opening just under the anterior half of the eye. Teeth small and bicuspid, 8–12 in a single row in the upper jaw (median = 11, holotype = 11), 18–23 in a single row in the lower jaw (median = 20, holotype = 18). Dorsal and anal fins originate in the posterior half of the body (1.5 ≤ standard length/pre–dorsal distance ≤ 1.6 and 1.6 ≤ standard length/pre–anal distance ≤ 1.7, respectively). Pre–dorsal distance slightly greater than the pre–anal distance. Dorsal fin with 20–22 branched rays (median = 21, holotype = 22). Anal fin with 27–29 branched rays (median = 28, holotype = 29). Scales cover the body, except for the head. Lateral line visible and complete with 36–38 (holotype = 38) pored scales along its length. Ten to 14 scales (average = 12, holotype = 11) between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (1.9 ≤ Caudal peduncle length/caudal peduncle distance ≤ 2.3, average = 2.1, holotype = 2.1). Twelve scales around the caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans clustered into the three distinct “rosettes” of Harder (1968).

Body background color pinkish–gray, darker dorsally. Pigmentation pattern consisting of three characteristic black patches: (1) a distinct ovoid black mark below the anterior base of the dorsal fin; (2) a small black mark at the base of the pectoral fin; and (3) an ovoid black mark centered at the base of the caudal fin, which does not extend on the upper and lower lobes. Fins translucent.

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

Description

Diagnostic Description

Petrocephalus odzalaensis is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin shorter than anal fin. Dorsal fin with a maximum of 22 branched rays (range = 20–22). Anal fin with a minimum of 27 branched rays (range = 27–29). Mouth sub–terminal; ratio between head length and mouth position is between 4.2 and 5.0. Eye small (3.7 ≤ head length/eye diameter ≤ 4.2). Body pinkish–gray, darker dorsally, with the presence of three distinct pigmentation patches: (1) a distinct ovoid black mark situated below the anterior base of the dorsal fin on each side of the body; (2) a small black mark at the base of each pectoral fin; (3) an ovoid black mark on each side that is centered at the base of the caudal fin, not extending onto the upper and lower lobes of this fin. EOD of normal polarity, appearing triphasic at low gain, with two main phases and a small third phase. A final, fourth phase may be present, but it is always extremely small (< 1.5% of total peak–peak amplitude).

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

Electric Organ Discharge

The EOD waveform is typical for the genus, similar to EODs produced by many other Petrocephalus species. The total EOD duration ranges from 0.231 to 0.339 msec, based on 1.5% voltage deviations from baseline relative to peak-peak amplitude. No EOD sex differences are apparent in the specimens recorded thus far.

Histological examination confirms that electrocytes are type NPp

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

Size

To 99.3 mm SL

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

Look Alikes

Based on museum records from the Congo basin, Petrocephalus odzalaensis has been misidentified as Petrocephalus simus in several instances. The latter species is endemic to the Lower Guinea province.

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

Ecology and Distribution

Distribution

Endemic to the central Congo basin.

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

Evolution and Systematics

Phylogenetic Relationships

Petrocephalus odzalaensis forms a monophyletic group with Petrocephalus binotatus and Petrocephalus balayi.

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

References

Harder, W. (2000).  The Mormyridae and other Osteoglossomorpha (CD-ROM). World Biodiversity Database, CD-ROM Series. 2000, New York: Springer Verlag, ETI-UNESCO.
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.
 
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