Petrocephalus zakoni, 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 : 9-12

Petrocephalus zakoni n. sp.

[Odzala field identification and in Lavoué et al. (2008): Petrocephalus sp. 2, OTU 2]

Images. Fig. 4 A, photo of a live specimen from Odzala and Fig. 4 B, photo of the preserved holotype (CU 88101).

Type material. Holotype, CU 88101 (morpho, EOD), male, 86.0 mm SL. Republic of the Congo, small channel around island in Lékoli River ( Congo basin), Odzala National Park, (0.62° N, 14.95° E). J.P. Friel, S. Lavoué & J.P. Sullivan coll., 20 August 2002.

Paratypes. CU 88036 (morpho, EOD), sex undet., 81.4 mm SL; CU 88042 (morpho, EOD), male, 78.6 mm SL; CU 88037 (morpho, EOD), sex undet., 79.6 mm SL; CU 88077 (morpho), male, 84.8 mm SL. Republic of the Congo, Pandaka River ( Congo basin), Odzala National Park, (0.62° N, 14.92° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August 2002. CU 88104 (morpho, EOD), sex undet., 83.5 mm SL; AMNH 251426 (ex CU 88100) (morpho, EOD), male, 73.7 mm SL; AMNH 251427 (ex CU 88103) (morpho, EOD), sex undet., 77.2 mm SL. Republic of the Congo, small channel around island in Lékoli River ( Congo basin), Odzala National Park (0.62 ° N, 14.95 ° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August 2002. CU 88093 (morpho, EOD), male, 67.4 mm SL; AMNH 251424 (ex CU 88088) (morpho, EOD), sex undet., 75.8 mm SL; AMNH 251425 (ex CU 88090) (morpho, EOD), male, 76.0 mm SL. Republic of the Congo, small channel around island in Lékoli River ( Congo basin), Odzala National Park (0.62 ° N, 14.92 ° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., August 2002.

Other specimens. We examined 34 other specimens from Odzala National Park (specimen list provided in the section "additional material examined").

Diagnosis. Petrocephalus zakoni n. sp. is distinguished from all other Petrocephalus species in Central Africa (Lower Guinea and Congo provinces) by the following combination of characteristics. Dorsal fin with 23 or 24 branched rays. Anal fin with 27 or 28 branched rays. Eye large (HL/ED ≤ 3.3, range = 3.1–3.3). Mouth small (4.4 ≤ HL/MW, range = 4.4–5.0). Ten teeth or fewer (range = 6–10) in the upper jaw. Twentytwo teeth or fewer (range = 18–22) in the lower jaw. Unique pigmentation pattern consisting of three well defined black patches ( Fig. 4 A): (1) an intense dark mark on each side of the body close to the anterior base of the dorsal fin, often extending onto the first dorsal rays, forming a characteristic saddle across the dorsum; (2) a mark on each side of the body at the base of the pectoral fin; (3) a crescent-shaped mark on each side of the body centered at the base of the caudal fin, extending onto the upper and lower parts of the caudal fin. EOD of normal polarity (i.e., first major phase head-positive).

Description. Morphometric ratios and meristic data are given in Table 2 for the holotype and paratypes separately. Petrocephalus zakoni n. sp. is a small sized species within the genus (maximum SL in the type series = 86.0 mm, maximum SL observed in all specimens = 90 mm). Body ovoid, longer than high (2.5 ≤ SL/ H ≤ 2.8, paratype average = 2.6, holotype =2.8) and laterally compressed. Head length between 3.4 and 3.7 times in standard length (paratype average = 3.6, holotype = 3.6). Eye large compared to many Petrocephalus species (3.1 ≤ HL/ED ≤ 3.3, paratype average = 3.2, holotype = 3.2). Snout short (6.1 ≤ HL/SNL ≤ 8.5, paratype average = 7.2, holotype = 6.2) and round. Mouth small (4.4 ≤ HL/MW ≤ 5.0, paratype average = 4.7, holotype = 4.5) and sub-terminal, opening under the posterior half of the eye. Teeth small and bicuspid, 6–10 (paratype median = 8, holotype = 9) in a single row in the upper jaw, 18–22 (paratype median = 19, holotype = 20) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.6 ≤ SL/PDD ≤ 1.7, paratype average and holotype = 1.6; 1.6 ≤ SL/PAD ≤ 1.7, paratype average and holotype = 1.6). Pre-dorsal distance roughly equal to the pre-anal distance. Dorsal fin with 23 or 24 branched rays (median = 23, holotype = 24). Anal fin with 27 or 28 branched rays (median = 27, holotype = 28). Scales cover the body, except for the head. Lateral line visible and complete with 36–38 pored scales along its length (paratype average = 37, holotype = 38). Twelve to 14 scales (paratype average = 13, holotype = 14) 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 = 2.2). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation. Knollenorgans on the head are not clustered into "rosettes" but, instead, appear as isolated receptor pores, the character state observed in the Mormyrinae .

Live coloration ( Fig. 4 A). Body uniformly white-silver, with the presence of three characteristic pigmentation marks: (1) a very distinctive black mark just below the anterior base of the dorsal fin on each side, often extending onto the first dorsal rays and making contact over the dorsum with the contralateral mark; (2) a blackish mark, sometimes weak but always visible, at the base of the pectoral fins; (3) a crescentshaped black mark centered at the base of the caudal fin on each side, extending onto the upper and lower parts of the caudal fin. Fins otherwise translucent.

Distribution ( Fig. 1 ). Apparently endemic to the Congo basin. Abundant in Odzala. We collected P. zakoni n. sp. at several localities along the main channel of the Lékoli River at night. Elsewhere in the Congo basin, we have identified specimens of P. z a k o n i n. sp. from the Lower Congo (Pool Malebo) and from the Sangha River basin (unpublished observations).

Electric organ discharge ( Fig. 4 C). EOD waveforms produced by P. zakoni n. sp. are of relatively short duration among Petrocephalus (range = 0.164–0.281 msec), but they are, nevertheless, very similar in waveform to the EODs of several other Petrocephalus species. EOD sex differences are not apparent in the Odzala population. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008). Electrocytes are assumed to be of type NPp based on characteristics of the EOD, although electrocyte anatomy has not yet been confirmed histologically.

Remarks. Given our identification of specimens from the Lower Congo River and the Dzangha-Sangha Reserve (Sangha River), Petrocephalus zakoni n. sp. is likely a common species in the Congo basin. This species has been previously misidentified as Petrocephalus christyi Boulenger, 1920 because its body proportions are similar to those of P. christyi . In addition, both species exhibit an intense sub-dorsal melanin marking on the flank. Nevertheless, these species can be distinguished by the presence of a black spot at the base of the pectoral fins in P. zakoni n. sp. (absent in P. christyi ), the shape of the sub-dorsal marking (ovoid to saddle-shaped versus rounded in P. christyi ), the waveshape of the EOD (with two main phases and a weak third phase in P. zakoni versus four phases in P. christyi ) and presence/absence of Knollenorgan rosettes on the head (absent in P. zakoni versus present in P. christyi ).

Holotype (m) Paratypes (n=10)

Min–Max Mean Std–Dev Min–Max Median

Meristic counts:

Number of scale rows between the anterior base of 14 12–14 13 the anal fin and the lateral line (SDL)

Number of teeth in the upper jaw (TUJ) 9 6–10 8 Number of teeth in the lower jaw (TLJ) 20 18–22 19 Etymology. Named in honor of Harold H. Zakon. In addition to Professor Zakon’s many contributions to neuroethology, we recognize the significance of his recent work ( Zakon et al., 2006), which inspires a new area of research on genes that underlie electrolocation and electrical communication in gymnotiform and mormyroid fishes.

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 4. Petrocephalus zakoni 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 88101; 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 2. Principal morphometric ratios and meristic counts for the holotype (CU 88101) and 10 paratypes (CU 88104, CU 88093, CU 88036, CU 88077, CU 88042, CU 88037, AMNH 250920, AMNH 250921, AMNH 250922, AMNH 250923) of Petrocephalus zakoni n. sp. (Abbreviations: m = male; Std – Dev = standard deviation; Min – Max = minimum – maximum).

Standard length (mm)	86.0	67.4–84.8	77.8	5.1
Head length (mm)	23.8	19.7–24.0	21.9	1.5
Ratio of standard length (SL):
SL/body height (H)	2.8	2.5–2.7	2.6	0.1
SL/head length (HL)	3.6	3.4–3.7	3.6	0.1
SL/pre-dorsal distance (PDD)	1.6	1.6–1.7	1.6	0.0
SL/pre-anal distance (PAD)	1.6	1.6–1.7	1.6	0.0
SL/dorsal fin length (DFL)	4.2	4.0–4.3	4.1	0.1
SL/anal fin length (AFL)	3.5	3.3–3.5	3.4	0.1
SL/caudal peduncle length (CPL)	6.9	6.4–7.0	6.7	0.2
SL/mouth width (MW)	16.2	15.5–17.6	16.6	0.7
Ratio of head length (HL):
HL/snout length (SNL)	6.2	6.1–8.5	7.2	0.7
HL/mouth width (MW)	4.5	4.4–5.0	4.7	0.2
HL/eye diameter (ED)	3.2	3.1–3.3	3.2	0.1
HL/interorbital width (IOW)	3.0	2.4–3.2	2.9	0.2
HL/head width (HW)	1.9	1.8–2.0	1.9	0.0
HL/mouth position (MP)	3.4	3.2–3.9	3.5	0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD)	2.2	1.9–2.3	2.1	0.1