Petrocephalus arnegardi, Lavoue, Sebastien & Sullivan, John P., 2014

Lavoue, Sebastien & Sullivan, John P., 2014, Petrocephalus boboto and Petrocephalus arnegardi, two new species of African electric fish (Osteoglossomorpha, Mormyridae) from the Congo River basin, ZooKeys 400, pp. 43-65 : 49-54

Petrocephalus arnegardi sp. n. Figs 2and 5; Table 1

Petrocephalus sp. 1, OTU 1 in Lavoué et al. (2008).

Petrocephalus binotatus in Lavoué et al. (2010), Lavoué (2011, 2012), Carlson et al. (2011).

Holotype.

CUMV 88074, tag no. 5074, 72.6 mm SL, male, Republic of the Congo: Cuvette Ouest, Congo River basin, Pandaka River, Odzala-Kokua National Park, 0.62°N, 14.92°E, Friel et al., August 2002.

Paratypes

(17). Republic of the Congo: Cuvette-Ouest: Congo River basin: CUMV 88076, tag no. 5076, 69.6 mm SL, male, same data as holotype; CUMV 88041, tag no. 5120, 85.1 mm SL, sex undetermined, same data as holotype; CUMV 88080, tag no. 5083, 72.0 mm SL, male, same data as holotype; CUMV 88032, tag no. 5101, 73.0 mm SL, male, same data as holotype; CUMV 87785, tag no. 5097, 71.3 mm SL, sex undetermined, same data as holotype; CUMV 88031, tag no. 5100, 73.7 mm SL, sex undetermined, same data as holotype; CUMV 88079, tag no. 5082, 74.8 mm SL, sex undetermined, Lékénie River at Mboko landing, Odzala-Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002; CUMV 88063, tag no. 5197, 64.9 mm SL, sex undetermined, Lékénie River at Mboko landing, Odzala- Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002; CUMV 88065, tag no. 5002, 70.7 mm SL, sex undetermined [cytochrome b gene determined], Lékénie River at Mboko landing, Odzala-Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002; CUMV 88064, tag no. 5001, 63.9 mm SL, male [cytochrome b gene determined], Lékénie River at Mboko landing, Odzala-Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002; CUMV 88052, tag no. 5158, 75.1 mm SL, male, Lékénie River at Mboko landing, Odzala-Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002; CUMV 88053, tag no. 5159, 69.3 mm SL, male, Lékénie River at Mboko landing, Odzala-Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002; CUMV 88123, tag no. 5377, 68.9 mm SL, male, Lékoli River, Odzala-Kokua National Park, 0.61°N, 14.93°E, Friel et al., August 2002; CUMV 87838, tag no. 5404, 90.1 mm SL, male, Lokoué River, Odzala-Kokua National Park, 0.90°N, 15.12°E, Friel et al., August 2002; CUMV 87830, tag no. 5395, 72.3 mm SL, sex undetermined, Lokoué River, Odzala-Kokua National Park, 0.90°N, 15.12°E, Friel et al., August 2002; CUMV 92390, two specimens, tag no. 6133, 62.8 mm SL, male [cytochrome b gene determined] and tag no. 6134, 67.5 mm SL, male [cytochrome b gene determined], mouth of the Lékéni River near the Lékoli River, Odzala-Kokua National Park, 0.62°N, 14.91°E, Arnegard et al., June 2006.

Other specimens

(18). Republic of the Congo: Cuvette-Ouest: Congo River basin: Lékénie River at Mboko landing, Odzala-Kokua National Park, 0.62°N, 14.90°E, Friel et al., August 2002: CUMV 88066, tag no. 5028, 59.0 mm SL, sex undetermined; CUMV 88046, tag no. 5126, SL not measured, sex undetermined; Republic of the Congo: Cuvette-Ouest: Congo River basin: Pandaka River, Odzala-Kokua National Park, 0.62°N, 14.92°E, Friel et al., August 2002: CUMV 88075, tag no. 5075, 71.0 mm SL, sex undetermined; CUMV 88081, tag no. 5084, 73.0 mm SL, male; CUMV 88082, tag no. 5085, 54.0 mm SL, sex undetermined; CUMV 88028, tag no. 5096, 74.0 mm SL, male; CUMV 88029, tag no. 5098, 74.0 mm SL, male; CUMV 88043, tag no. 5122, 73.0 mm SL, male; CUMV 88044, tag no. 5123, 66.0 mm SL, male; CUMV 88045, tag no. 5124, 73.0 mm SL, male; Republic of the Congo: Cuvette-Ouest: Congo River basin: Lokoué River, Odzala-Kokua National Park, 0.90°N, 15.12°E, Friel et al., August 2002: CUMV 88125, tag no. 5396, 74.0 mm SL, male; Republic of the Congo: Cuvette-Ouest: Congo River basin: small channel around island in Lékoli River, Odzala-Kokua National Park, 0.62°N, 14.92°E, Friel et al., August 2002: CUMV 88107, tag no. 5276, SL not measured, male; Republic of the Congo: Cuvette-Ouest: Congo River basin: Lékoli River, Odzala-Kokua National Park, 0.61°N, 14.93°E, Friel et al., August 2002: CUMV 88067, tag no. 5029, 59.0 mm SL, sex undetermined; CUMV 88068, tag no. 5030, 59.0 mm SL, sex undetermined; CUMV 88069, tag no. 5031, 57.0 mm SL, sex undetermined; Republic of the Congo: Cuvette-Ouest: Congo River basin: small stream entering Mambili River from the east between Moba and Lokoué, 0.87°N, 15.11°E, Friel et al. August 2002: CUMV 88128, tag no. 5423, 70.0 mm SL, male; Democratic Republic of Congo: Orientale Province: Congo basin: BMNH 2013.8.29.34, tag no. JPS-497, 76.0 mm SL, male [cytochrome b gene determined, no EOD recorded], Lifundu River, 5 km downstream of Yangambi, 0.76°N, 24.24°E, Lavoué & Thumitho, 11 September 2010; BMNH 2013.8.29.125, tag no. JPS-511, 48.9 mm SL, sex undetermined [cytochrome b gene determined], Congo River at Yangambi, 0.76°N, 24.24°E, Lavoué et al., 11 September 2010.

Diagnosis.

Petrocephalus arnegardi sp. n. is distinguished from all other Petrocephalus species of Central Africa by the following combination of characteristics. Pigmentation pattern comprising three well-defined, bilateral black patches: one usually distinct (sometimes reduced in size, but rarely absent) round/ovoid subdorsal black mark situated slightly anterior to dorsal, one black mark at the base of each pectoral fin, and one ovoid black mark centered at the base of caudal fin. Dorsal fin at least one third shorter than anal fin (AFL/DFL ≥ 1.5, range = 1.5-1.7). Dorsal fin with at least 20 branched rays but no more than 22. Anal fin with at least 30 branched rays (range = 30-34). Sixteen teeth or fewer (range = 8-16) in upper jaw, 25 teeth or fewer (range = 20-25) in lower jaw. Eye relatively large (HL/ED ≤ 4.7, range = 3.5-4.7). Mouth subterminal; ratio of head length to mouth position (HL/MP) between 4.2 and 5.6. Mouth small (HL/MW ≥ 4.1, range = 4.1-5.0). EOD of normal polarity, mainly biphasic with sometimes the presence of a small-amplitude positive third phase.

Description.

This description is based on the material from Odzala-Kokua National Park in the Republic of the Congo. Morphometric ratios and meristic data for the holotype and 17 paratypes are presented in Table 1. Maximum SL observed = 90.1 mm, holotype = 72.6 mm). Body ovoid, longer than high (2.3 ≤ SL/H ≤ 2.8, average = 2.6, holotype = 2.5) and laterally compressed. Head length between 3.4 and 4.0 times in standard length (average = 3.6, holotype = 3.4). Snout short (6.5 ≤ HL/SNL ≤ 9.3, average = 7.5, holotype = 8.3) and round. Eye large (3.5 ≤ HL/ED ≤ 4.4, average = 4.0, holotype = 4.1). Mouth small (4.1 ≤ HL/MW ≤ 5.0, average = 4.6, holotype = 4.5), subterminal, opening under the anterior half of the eye. Teeth small and bicuspid, 8 to 16 (median = 10) in a single row in the upper jaw, 20 to 24 (median = 21) in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.4 ≤ SL/PDD ≤ 1.6 and 1.6 ≤ SL/PAD ≤ 1.7, respectively). Pre-dorsal distance slightly greater than the pre-anal distance (PDD/PAD = 1.1). Dorsal fin with 20-22 branched rays (median = 21). Anal fin with 31-34 branched rays (median = 32, holotype = 32). Scales cover the body, except for the head. Lateral line visible and complete with 34 to 38 pored scales along its length. Ten to 13 scales (median = 11), between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (1.8 ≤ CPL/CPD ≤ 2.5, average = 2.2, holotype = 2.2). Twelve scales around the caudal peduncle. Skin on head thick. The three rosettes of Knollenorgans, Augenrosette, Nackenrosette and Kehlrosette, are present on the head.

Electric organ discharge. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008) for specimens recorded in Odzala-Kokua National Park, including the holotype and paratypes (specimens listed in Suppl. material 1). Petrocephalus arnegardi sp. n. produces EOD waveforms largely similar to those of many species of this genus. In Odzala-Kokua, mean EOD duration ( ± std. dev.) is 0.330 ± 0.074 msec in sexually mature males and 0.270 ± 0.033 msec in other sex undetermined specimens. The EOD waveform characteristics of the only recorded specimen of Petrocephalus arnegardi sp. n. of Yangambi (Fig. 2B; EOD biphasic, relative height of peak 1 = 0.216, relative height of peak 2 = -0.784, duration of peak 1 = 0.185 msec, duration of peak 2 = 0.075 msec, total EOD duration = 0.260 msec) are similar to those of Odzala-Kokua specimens in all respects. Based on characteristics of the EODs, the electrocytes are assumed to have non-penetrating stalks and to be innervated posteriorly ( Sullivan et al. 2000).

Live coloration (Fig. 5; see also Fig. 3 in Lavoué et al. 2010). Body uniformly silvery white, with three distinct bilateral melanin marks: a distinct, ovoid black mark situated slightly anterior to the dorsal fin, sometimes covering only a few scales, a black spot at the base of the pectoral fin and a somewhat vertically oriented ovoid black mark centered at the base of the caudal fin that does not extend onto the upper and lower parts of the caudal fin. Fins hyaline.

Preserved coloration (Fig. 5; see also Fig. 3 in Lavoué et al. 2010). Body light brown, with head and dorsum slightly darker. Thick skin on head opaque. Numerous light melanophores on body, slightly larger ventrally from the snout to the anal fin. Fins whitish/opaque.

Distribution (Fig. 1). Endemic to the Congo River basin. Holotype and paratypes from Odzala-Kokua National Park (Republic of the Congo) where they were mainly collected along the main channel of the Lékoli River, northwestern Congo River basin. The two specimens collected at Yangambi will extend the distribution to the eastern part of the Congo basin’s central cuvette. Abundant in Odzala-Kokua but apparently rare at Yangambi ( Poll and Gosse 1963).

Phylogenetic affinities (Fig. 4). The Yangambi specimens and the Odzala-Kokua specimens of Petrocephalus arnegardi sp. n. are sister groups in the cytochrome b phylogenetic tree. Petrocephalus arnegardi sp. n. belongs to a clade containing Petrocephalus odzalaensis and Petrocephalus balayi , two other species with a similar melanin pattern composed of three distinct black marks, but it is only distantly related to Petrocephalus boboto sp. n. As previously noted, Petrocephalus binotatus is absent in this tree and its phylogenetic position is unknown.

Etymology.

This species is dedicated to Matthew E. Arnegard, our friend and colleague, in recognition of his contributions to study of mormyrid evolution and diversification (e.g., Arnegard et al. 2005; Arnegard and Carlson 2005; Arnegard et al. 2010a; Arnegard et al. 2010b). Matthew Arnegard is additionally a member of the " Mintotom Team": researchers associated with the Carl D. Hopkins Laboratory at Cornell University who have conducted field studies on African weakly electric fishes for more than 15 years. (" Mintotom " is the plural form of the word for mormyrid fish in the Fang language of West Central Africa.).

Comparisons.

As for Petrocephalus boboto sp. n., the presence of three dark spots in Petrocephalus arnegardi sp. n. distinguishes this species from most of its congeners. As for other species having a similar pattern of melanin marking, Petrocephalus arnegardi sp. n. can easily be distinguished from Petrocephalus zakoni by the presence of three electroreceptor rosettes on the head (versus absence of all three in Petrocephalus zakoni ) and a higher number of anal fin rays (a minimum of 30 in Petrocephalus arnegardi sp. n. versus a maximum of 28 in Petrocephalus zakoni ). Its high number of anal fin rays distinguishes Petrocephalus arnegardi sp. n. from Petrocephalus balayi and Petrocephalus odzalaensis (30-34 in Petrocephalus arnegardi sp. n. versus a maximum of 27 and 20 in Petrocephalus balayi and Petrocephalus odzalaensis , respectively). Petrocephalus balayi has a proportionally larger mouth (HL/MW = 2.7-3.9 versus 4.1-5.0 in Petrocephalus arnegardi sp. n.). Petrocephalus arnegardi sp. n. generally resembles to the holotype of Petrocephalus binotatus , leading Lavoué et al. (2010) to assign these specimens from the Odzala-Kokua National Park to Petrocephalus binotatus . However, Petrocephalus arnegardi sp. n. has a distinctly smaller mouth than Petrocephalus binotatus (HL/MW = 4.4-5.2 in Odzala-Kokua specimens and 4.2 and 4.5 in the two Yangambi specimens versus 3.2 in the holotype of Petrocephalus binotatus ) and a smaller interorbital width (HL/IOW ≥ 2.6 in Odzala-Kokua and Yangambi specimens versus 2.3 in the holotype of Petrocephalus binotatus ). The faded pigmentation in the preserved holotype of Petrocephalus binotatus precludes its accurate description and comparison (Fig. 6). Whereas a faded roundish black mark situated slightly anterior to the dorsal fin on each side of the flank and an ovoid black mark centered at the base of the caudal fin are visible on the preserved holotype, the presence of a black mark at the base of the pectoral fin is ambiguous (Fig. 6). In his description of Petrocephalus binotatus , Pellegrin (1924) mentioned the subdorsal mark and the mark at the base of the anal fin, but did not make reference to any black mark at the origin of the pectoral fin. The black mark at the base of the pectoral fin in Petrocephalus arnegardi sp. n. is always present and intense. Pellegrin also described the black mark at the base of the caudal fin as crescent-like, extending onto the upper and lower rays of this fin (see drawing in Pellegrin 1928) whereas on the holotype this mark appears more ovoid and does not seem to extend onto any fin rays (Fig. 6). Petrocephalus arnegardi sp. n. is distinguished from Petrocephalus boboto sp. n. by a distinctly smaller mouth (SL/MW ≥ 14.7, range = 14.7-18.4 versus 14.2 in Petrocephalus boboto sp. n.), a slightly larger interorbital distance (HL/IOW ≤ 3.9, mean = 3.2 versus 3.7 in Petrocephalus boboto sp. n.) and the presence of a well-defined Augenrosette (versus reduced in Petrocephalus boboto sp. n.). In our phylogenetic tree (Fig. 4), Petrocephalus boboto sp. n. is not the sister group of Petrocephalus arnegardi sp. n.