Petrocephalus odzalaensis, Lavoué, Sébastien, Sullivan, John P. & Arnegard, Matthew E., 2010

Lavoué, Sébastien, Sullivan, John P. & Arnegard, Matthew E., 2010, African weakly electric fishes of the genus Petrocephalus (Osteoglossomorpha: Mormyridae) of Odzala National Park, Republic of the Congo (Lékoli River, Congo River basin) with description of five new species, Zootaxa 2600, pp. 1-52 : 22-25

Petrocephalus odzalaensis n. sp.

[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 6, OTU 6]

Images. Fig. 8 A, photo of a live specimen from Odzala and Fig. 8 B, photo of the preserved holotype (CU 88048).

Type material. Holotype, CU 88048 (morpho, EOD), sex undet., 92.9 mm SL. Republic of the Congo, Lékénie River at Mboko débarcadère ( Congo basin), Odzala National Park, (0.62 ° N, 14.90 ° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August 2002.

Paratypes. CU 87850 (morpho, EOD), male, 90.1 mm SL; CU 87857 (morpho, EOD), male, 92.6 mm SL; CU 88050 (morpho, EOD), male, 90.4 mm SL; AMNH 251414 (ex CU 87843) (morpho, EOD), male, 87.0 mm SL; AMNH 251417 (ex CU 88056) (morpho, EOD), male, 87.6 mm SL; AMNH 251416 (ex CU 88054) (morpho, EOD), male, 97.6 mm SL; CU 88059 (morpho, EOD), male, 99.3 mm SL; AMNH 251415 (ex CU 87844) (morpho, EOD), male, 87.3 mm SL. Republic of the Congo, Lékénie River at Mboko débarcadère ( Congo basin), Odzala National Park, (0.62 ° N, 14.90 ° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August 2002. CU 88049 (morpho, EOD; caudal peduncle dissected by Lavoué et al. (2008) to sample electric organ for histological examination), male, 93.2 mm SL. Republic of the Congo, Lékénie River at Mboko débarcadère ( Congo basin), Odzala National Park, (0.62 ° N, 14.90 ° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., 12 August 2002.

Holotype (o) Paratypes (n=9)

Min–Max Mean Std–Dev Min–Max Median

Meristic counts:

Dorsal fin branched rays (DR) 22 20–22 21 Anal fin branched rays (AR) 29 27–29 28 Number of scales in the lateral line (SLL) 38 36–38 37 Number of scale rows between the anterior base of 11 10–14 12 the anal fin and the lateral line (SDL)

Number of teeth in the upper jaw (TUJ) 11 8–12 11 Number of teeth in the lower jaw (TLJ) 18 18–23 20 Other specimens. We examined 19 other specimens from Odzala National Park (specimen list provided in the section "additional material examined").

Diagnosis. Petrocephalus odzalaensis n. sp. 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 ≤ HL/ED ≤ 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-to-peak amplitude).

Description. Morphometric ratios and meristic data for the holotype and paratypes are presented in Table 6 . Petrocephalus odzalaensis n. sp. is a medium sized species within the genus (maximum SL observed = 99.3 mm; holotype = 92.9 mm). Body ovoid, longer than high (2.6 ≤ SL/H ≤ 2.9, paratype average = 2.8, holotype = 2.6) and laterally compressed. Head length between 3.7 and 4.0 times in standard length (paratype average = 3.9, holotype = 4.0). Snout short (6.2 ≤ HL/SNL ≤ 8.3, paratype average = 7.3, holotype = 6.6) and round. Mouth small (4.0 ≤ HL/MW ≤ 4.8, paratype 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 (paratype median = 11, holotype = 11), 18–23 in a single row in the lower jaw (paratype median = 20, holotype = 18). Dorsal and anal fins originate in the posterior half of the body (1.5 ≤ SL/PDD ≤ 1.6 and 1.6 ≤ SL/PAD ≤ 1.7, respectively). Pre-dorsal distance slightly greater than the pre–anal distance (1.0 ≤ PDD/PAD ≤ 1.1). Dorsal fin with 20–22 branched rays (paratype median = 21, holotype = 22). Anal fin with 27–29 branched rays (paratype 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 (paratype average = 12, holotype = 11) between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (1.9 ≤ CPL/ CPD ≤ 2.3, paratype 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).

Live coloration ( Fig. 8 A). 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 onto the upper and lower lobes. Fins translucent.

Distribution ( Fig. 1 ). Endemic to the Congo basin. Abundant in Odzala. We collected P. odzalaensis n. sp. at several localities along the main course of the Lékoli River and in some small tributary creeks flowing through forest.

Electric organ discharge ( Fig. 8 C). The EOD waveform is typical for the genus, similar to EODs produced by many other Petrocephalus species. 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. Lavoué et al. (2008) provide additional statistics for waveform landmarks and other EOD measurements. Histological examination confirms that electrocytes are type NPp ( Lavoué et al., 2008).

Remarks. Based on museum records from the Congo basin (pers. obs.), Petrocephalus odzalaensis has been misidentified as Petrocephalus simus in several instances. The latter species is endemic to the Lower Guinea province ( Lavoué et al., 2004).

Etymology. Named for Odzala National Park.

Figures

FIGURE 1. Map of Africa (right) showing the entire Congo River and its main tributaries together with the neighboring Lower Guinea province (first inset at center). The boundary between the Congo and Lower Guinea provinces is shown by a dashed line. Filled black circles indicate type localities for all Petrocephalus species that were described from either province and were considered valid just prior to the present study. Exact type localities are unknown for P. b a l a y i and P. sauvagii. Based on our understanding of the chronology of Central African exploration at the time of the descriptions, we estimate these type localities to be the following: the vicinity of Pool Malebo on the Lower Congo River near the modern cities of Brazzaville and Kinshasa [4.25 ° S, 15.29 ° E] for P. sauvagii; and the vicinity of the present-day city Lambaréné on the Lower Ogooué River [0.7 ° S, 10.22 ° E] for P. b a l a y i. Second inset at the far left: detailed map of Odzala National Park, located in the Congo River basin. Within the boundaries of the park, forest is shown in green and savannah in yellow. The red oval indicates our collection area (a segment of the Lékoli drainage system, including the lower parts of two of its tributaries, the Pandaka and Lékénie Rivers).

FIGURE 8. Petrocephalus odzalaensis n. sp. of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Photograph of a live specimen (no scale). B. Photograph of the preserved holotype (CU 88048; scale bar = 1.0 cm). C. EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).

Tables

TABLE 6. Principal morphometric ratios and meristic counts for the holotype (CU 88048) and nine paratypes (CU 87857, CU 88049, CU 87850, CU 88050, CU 88059, AMNH 250928, AMNH 250929, AMNH 250930, AMNH 250931) of Petrocephalus odzalaensis n. sp. (Abbreviations: o = sex category " other " [i. e., not an obvious mature male, but rather a female or immature male]; Std – Dev = standard deviation; Min – Max = minimum – maximum).

Standard length (mm)	92.9	87.0–99.3	91.7 4.5
Head length (mm)	23.3	22.7–26.6	23.7 1.6
Ratio of standard length (SL):
SL/body height (H)	2.6	2.7–2.9	2.8 0.0
SL/head length (HL)	4.0	3.7–4.0	3.9 0.1
SL/pre-dorsal distance (PDD)	1.6	1.5–1.6	1.6 0.0
SL/pre-anal distance (PAD)	1.7	1.6–1.7	1.6 0.0
SL/dorsal fin length (DFL)	4.5	4.4–4.7	4.6 0.2
SL/anal fin length (AFL)	3.3	3.3–3.6	3.4 0.1
SL/caudal peduncle length (CPL)	6.9	6.1–7.1	6.8 0.3
SL/mouth width (MW)	17.4	16.0–18.3	16.8 0.8
Ratio of head length (HL):
HL/snout length (SNL)	6.6	6.2–8.3	7.3 0.7
HL/mouth width (MW)	4.3	4.0–4.8	4.3 0.2
HL/eye diameter (ED)	3.7	3.8–4.2	4.0 0.1
HL/interorbital width (IOW)	2.7	2.5–3.0	2.8 0.2
HL/head width (HW)	1.7	1.7–1.8	1.7 0.1
HL/mouth position (MP)	4.7	4.2–5.0	4.5 0.3
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD)	2.1	1.9–2.3	2.1 0.1