Petrocephalus arnegardi Lavoué & Sullivan 2014

Diagnosis: Petrocephalus arnegardi 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 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; dorsal fin with at least 20 branched rays but no more than 22; anal fin with at least 30 branched rays; 16 teeth or fewer in upper jaw, 25 teeth or fewer in lower jaw; eye relatively large, ration head length and eye-diameter less than 4.7; mouth subterminal; ration of head length to mouth position between 4.2 and 5.6; mouth small, ration head length and mouth width more than 4.1; and EOD of normal polarity, mainly biphasic with sometimes the presence of a small-amplitude positive third phase (Ref. 96601).Description: Body ovoid, longer than high, its ration between 2.3 and 2.8, and laterally compressed (Ref. 96601). Head length between 3.4 and 4.0 times in standard length (Ref. 96601). Snout short, ration head length and snout length between 6.5 and 9.3, and round (Ref. 96601). Eye large, the ration head length and eye-diameter between 3.5 and 4.4 (Ref. 96601). Mouth small, the ration head length and mouth width between 4.1 and 5.0, subterminal, opening under the anterior half of the eye; teeth small and bicuspid, 8 to 16 in a single row in the upper jaw, 20-24 in the lower jaw (Ref. 96601). Caudal peduncle thin, the ration caudal peduncle depth and caudal peduncle height between 1.8 and 2.5 (Ref. 96601). Dosral and anal fins originate in the posterior half of the body; pre-dorsal distance slightly greater than the pre-anal distance; dorsal fin with 20-22 branched rays; anal fin with 31-34 branched rays (Ref. 96601). Scales cover the body, except for the head; lateral line visible and complete with 34 and 38 pored scales along its length; 10 to 13 scales between the anterior base of the anal fin and the lateral line; 12 scales around the caudal peduncle (Ref. 96601). Skin on head thick (Ref. 96601). The three rosettes of knollenorgans are present on the head (Ref. 96601).Colouration: 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 orientated 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 (Ref. 96601). Preserved colouration of 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 (Ref. 96601).

fisheries:

Petrocephalus arnegardi is a species of electric fish in the genus Petrocephalus native to the Central Congo River basin. It is found in middle Congo River and in the Likouala River drainage, in the Democratic Republic of the Congo and Republic of the Congo. It is named after Matthew Arnegard, an expert on elephantfishes.

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.