Petrocephalus boboto, 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 : 46-49

Petrocephalus boboto sp. n. Figs 2and 3; Table 1

Holotype.

CUMV 96774, tag no. JPS-10-426, 56.9 mm SL, sex undetermined, Orientale Province, Democratic Republic of Congo: Congo River at Yangambi, 0.76°N, 24.24°E, Lavoué et al., 10 September 2010.

Diagnosis.

Petrocephalus boboto sp. n. is distinguished from all other Petrocephalus species of Central Africa (i.e., Lower Guinea and Congo provinces) by the following combination of characteristics: three distinctive bilateral black spots on body, one at origin of the pectoral fin, one at origin of caudal fin and one on flank just below anterior part of dorsal fin; two distinct electoreceptive rosettes in head (i.e., Nakenrosette and Khelrosette), the third rosette (Augenrosette) reduced in size to few knollenorgan pores; 23 branched rays in dorsal fin and 34 branched rays in anal fin; triphasic EOD waveform of normal polarity (i.e. first phase head-positive).

Description.

Morphometric ratios and meristic data for holotype presented in Table 1. Standard length = 56.9 mm. Sex undetermined: specimen lacks anal fin “notch” present in mature males, but may be juvenile. Body ovoid, 2.7 times longer than high and laterally compressed. Head length 3.3 times in standard length. Snout short (HL/SNL = 6.6) and round. Mouth small (HL/MW = 4.4), subterminal, opening under anterior half of eye. Teeth small and bicuspid, 13 in single row in upper jaw, 24 in single row in lower jaw. Nostrils closely set (distance between nostrils = 0.4 mm) with the posterior one very close to eye (distance between posterior nostril and eye = 0.1 mm). Dorsal and anal fins originating in posterior half of body (SL/PDD = 1.6 and SL/PAD = 1.8). Pre-dorsal distance slightly greater than pre-anal distance (PDD/PAD = 1.1). Dorsal fin with 23 branched rays. Anal fin with 34 branched rays. Pectoral fins with 9 rays. Pelvic fin with 6 rays. Distance between pelvic fin and anal fin = 10.1 mm. Distance between pectoral fin and anal fin = 16.4 mm. Scales cover body, except for head. Lateral line visible and complete with 34 pored scales along its length. Ten scales around caudal peduncle. Ten scales between anterior base of anal fin and lateral line. Caudal peduncle narrow (CPL/CPD = 1.6). Thick skin on head. Knollenorgans visible, clustered into two distinct rosettes, Nackenrosette and Kehlrosettes as described in Harder (1968). Knollenorgan pores in front of eye not highly condensed in the form of a discernable Augenrosette.

Electric organ discharge (Fig. 2A). Short triphasic EOD waveform, first phase head-positive. Relative height of peak 1 = 0.241, relative height of peak 2 = -0.759, relative height of peak 3 = 0.053, duration of peak 1 = 0.137 msec, duration of peak 2 = 0.041 msec, duration of peak 3 = 0.079 msec, total EOD duration = 0.257 msec. Based on characteristics of the EOD, the electrocytes are assumed to have non-penetrating stalks and to be innervated posteriorly ( Sullivan et al. 2000).

Live coloration (Fig. 3). Body background color uniformly gray/silver with metallic reflection on the flanks and head. Light melanophores densely and evenly distributed on body, slightly larger on head. Three distinct black marks on each side of the body, one at the base of the pectoral fins, one at the base of the caudal fin and one subdorsal, below the first anterior rays of the dorsal fin. All fins hyaline.

Preserved coloration (Fig. 3). Background beige with dorsum slightly darker. Numerous light melanophores visible all over body. Thick skin on head and fins opaque. Three distinct melanin marks on side of body distinctly visible.

Distribution

(Fig. 1). Holotype (and only specimen known) of Petrocephalus boboto sp. n. collected from the main channel of the Congo River, at Yangambi, Orientale Province, Democratic Republic of Congo.

Phylogenetic affinities

(Fig. 4). Petrocephalus boboto sp. n. represents a deep lineage within the genus Petrocephalus not closely related to any of the four described species exhibiting a similar pattern of markings: Petrocephalus zakoni , Petrocephalus odzalaensis , Petrocephalus balayi and Petrocephalus arnegardi sp. n. However, it is worth noting that Petrocephalus binotatus , the fifth species with a potentially similar pigmentation, is not included in this tree and the phylogenetic position of this species is unresolved.

Etymology.

The name boboto is a word in Lingala, the language spoken at the type locality of Petrocephalus boboto sp. n., meaning “peace,” alluding to the right of all people of D.R. Congo to live in peace and safety.

Comparison.

The distinctive pattern of melanin markings of Petrocephalus boboto sp. n., having three dark spots-one at the origin of the pectoral fin, a second at the origin of the caudal fin, and a third on the flank just below the anterior base of the dorsal fin-distinguishes this species from most of its congeners. Only five other species of Petrocephalus similarly possess three black marks in these locations: Petrocephalus odzalaensis , Petrocephalus balayi , Petrocephalus zakoni , Petrocephalus binotatus and Petrocephalus arnegardi sp. n. (the comparison with Petrocephalus arnegardi sp. n. is provided under the description of this species). Petrocephalus boboto sp. n. can immediately be distinguished from Petrocephalus zakoni by the presence of two of the three electroreceptor rosettes on the head that are typical to Petrocephalus (versus absence of all three in Petrocephalus zakoni ) and a higher number of anal fin rays (33 in Petrocephalus boboto sp. n. versus a maximum of 28 in Petrocephalus zakoni ). Petrocephalus boboto sp. n. can be distinguished from Petrocephalus balayi and Petrocephalus odzalaensis by its higher number of anal fin rays (33 in Petrocephalus boboto sp. n. versus a maximum of 27 and 20 in Petrocephalus balayi and Petrocephalus odzalaensis , respectively). Petrocephalus balayi also has a proportionally larger mouth (HL/MW = 2.7-3.9, mean = 3.3 versus 4.4 in Petrocephalus boboto sp. n.). Petrocephalus odzalaensis has a proportionally wider head (HL/IOW = 2.5-3.0, mean = 2.8 and HL/HW = 1.7-1.8, mean = 1.7 versus 3.7 and 2.7 in Petrocephalus boboto sp. n., respectively) and its body background color is more pinkish rather than gray/silver in Petrocephalus boboto sp. n. Petrocephalus boboto sp. n. is distinguished from the holotype of Petrocephalus binotatus by a smaller mouth (SL/MW = 14.2 and HL/MW = 4.4 versus 11.6 and 3.2, respectively, in the holotype of Petrocephalus binotatus ), a smaller eye (HL/ED = 4.4 versus 3.6 in the holotype of Petrocephalus binotatus ), and a smaller interorbital distance (HL/IOW = 3.7 versus 2.3 in the holotype of Petrocephalus binotatus ).

The holotype of Petrocephalus boboto sp. n. is smaller than the holotype of Petrocephalus binotatus . The differences between Petrocephalus boboto sp. n. and Petrocephalus binotatus are unlikely to be the result of growth allometry since allometric differences have only been observed with respect to the number of teeth in some species of Petrocephalus ( Bigorne and Paugy 1991), a character that does not differentiate these two species. Although we are confident of the specific distinction between Petrocephalus boboto sp. n. and Petrocephalus binotatus , more specimens are needed to better characterize the morphological, molecular and electrophysiological differences between them.