Parauchenoglanis stiassnyae, Modimo & Bernt & Monsembula Iyaba & Mbimbi & Liyandja, 2024, Modimo & Bernt & Monsembula Iyaba & Mbimbi & Liyandja, 2024

Modimo, Myriam Y., Bernt, Maxwell J., Monsembula Iyaba, Raoul J. C., Mbimbi, José J. M. M. & Liyandja, Tobit L. D., 2024, Parauchenoglanis stiassnyae (Siluriformes: Auchenoglanididae): A new species of giraffe catfish from Mfimi-Lukenie basin, central Africa, Democratic Republic of Congo, Journal of Fish Biology 105 (4), pp. 1227-1239 : 1230-1237

RESULTS

3.1 | Barcoding and phylogeny

After trimming, we obtained a final alignment of 641 bp, for 32 specimens, including 179 distinct patterns, 162 parsimony-informative, 20 singletons, and 459 constant sites. Both AIC and Bayesian Information Criterion (BIC) selected the transition model with unequal base frequencies, empirical codon frequencies counted from the data, and discrete gamma with four categories (TIM + F + G4) as the best-fit substitution model for the alignment. The percent divergence calculation estimated that P. stiassnyae sp. nov. COI sequences diverge by more than 8.8% from all other sampled specimens except one from the Itimbiri River ( KT193142 ), from which P. stiassnyae sp. nov. differs by only 2% (Table 2). Phylogenetic analyses retrieved the specimen from the Itimbiri River ( KT193142 ) as the sister to P. stiassnyae sp. nov., which together form the sister to P. balayi from the Kouilou-Niari River system in the Lower Guinean ichthyofaunal province (Figure 3). Further investigation is needed to establish if the Itimbiri River specimens and P. stiassnyae sp. nov. are conspecifics or not. We did not have access to the specimens from Itimbiri and could not morphologically verify their identification.

3.2 | Meristics

After removal of two invariant counts (unbranched and branched dorsal-fin rays), a PCA was performed on the five remaining meristic counts (caudal-fin rays, anal-fin rays, pre-anal vertebrae, caudal vertebrae, and total vertebrae) for all 55 specimens of the eight examined Parauchenoglanis species. We found that 98.5% of variation is explained by the first two principal components, with PC1 accounting for 94.9% and PC2 3.6% of variation. Differences in total, pre-anal, and caudal vertebrae counts contributed most to PC1 factor loadings, with the number of total and pre-anal vertebrae having the highest influence, whereas differences in the number of caudal vertebrae and anal-fin rays contributed most to PC2 loadings. A plot of PC1 against PC2 divided the eight examined Parauchenoglanis species into three groups: P. stiassnyae sp. nov. was the only member of the first group with the fewest total (28–29) and pre-anal (13–14) vertebrae; the second group, with intermediate total vertebral counts (33–35, mostly 33–34), contains P. longiceps and P. pantherinus ; the third group, with the highest vertebral count (35–38, most with more than 35) includes P. balayi , P. guttatus , P. punctatus , P. cf. punctatus _L3, and P. ubangensis (Figure 4).

3.3 | Morphometrics

A PCA was also performed on 42 morphometric measurements after removal of total length (TL), SL, and pectoral-spine length (due to spine damage) (Figure 5). The first six principal components accounted for 66.2% of total variation with PC1, PC2, and PC3 accounting for 25.1%, 12.7%, and 11.2% of variation, respectively. Differences in the interpectoral distance (5.6%), orbital diameter (4.8%), mouth width (4.6%), minimum caudal peduncle height (4.5%), pre-dorsal length (4.1%), and the head width (HW) (4%) contributed the most to PC1 factor loadings, whereas differences in interorbital distance (8.3%), preorbital head length (HL) (8.1%), HL (7.8%), anterior nostrils interdistance (7.6%), supraoccipital process–dorsal-fin interdistance (6.8%), and adipose-fin–caudal-fin interdistance (5.9%) contributed the most to PC2 factor loadings. Differences in pectoral-fin length (7.05%), orbital head height (6.1%), premaxillary toothplate width (5.9%), maximum caudal peduncle height (5.6%), prepectoral length (5.4%), and maximum body height (5.2%) contributed most to PC3 factor loadings. Overall, biplots of PC1 versus PC2 and PC1 versus PC3 divided species into three groups (Figure 5): the first group exclusively contained P. stiassnyae sp. nov., the second contained species from Lower Guinea ( P. balayi , P. guttatus , P. longiceps , and P. pantherinus ), whereas the third group contained all remaining species ( P. punctatus , P. cf. punctatus _L3, and P. ubangensis ).

3.4 | Taxonomic description

P. stiassnyae , sp. nov., Zoobank acession numbers: urn:lsid:zoobank.org:act: and urn:lsid:zoobank.org:pub:.

N. macrostoma : Stiassny, Alter, Liyandja, et al., 2021 and Stiassny, Alter, Monsembula, & Liyandja, 2021.

3.4.1 | Holotype

AMNH 278139 (AMCC 284823), 64.72 mm SL, main channel of the Ndzaa River over mud and plant debris, in forest habitat , 4.6 km upstream of the Ndzaa confluence with the Mfimi River, Kutu Territory , Mai-Ndombe Province, D. R. Congo, 02 48 ' 17.3 '' S, 018 11 ' 08.0 '' E, August 10, 2021, M. Y. Modimo.

3.4.2 | Paratypes

N = 13. All Mai-Ndombe Province, D. R. Congo: AMNH 278138 (AMCC 284847), 60.22 mm SL, main channel of the Ndzaa River over mud and plant debris, in forest habitat , 6.9 km upstream of the Ndzaa River confluence with the Mfimi River, Kutu Territory , 02 48 ' 55.8 '' S, 018 11 ' 19.0 '' E, August 8, 2021, M. Y. Modimo; AMNH 274612 (AMCC 258190), 70.83 mm SL, main channel of the Mfimi River around the Nioki Port, in grass habitat , Kutu Territory , 02 43 ' 25.4 '' S, 017 41 ' 38.5 '' E, July 20, 2018, Fishermen; AMNH 269908 ( two specimens), 66.24–66.28 mm SL, Lebéé River (tributary of Mfimi River) near Kilako village in about 16.7 km downstream of the town of Kutu, over mud, in grass habitat , Kutu Territory , 02 48 ' 30.92 '' S, 018 01 ' 34.90 '' E, August 8, 2015, R. Monsembula et al.; AMNH 278137 (1, CT-scanned), 73.9 mm SL, main channel of the Ndzaa River over mud and vegetal debris, in forest habitat , in about 7.3 km upstream of the Ndzaa River confluence with the Lukeni River, Kutu Territory , 02 49 ' 29.4 '' S, 018 11 ' 31.7 '' E, August 7, 2021, M. Y. Modimo; AMNH 278164 (1), 71.7 mm SL, main channel of the Ndzaa River over mud and vegetal debris , in forest habitat , in about 5.5 km upstream of the Ndzaa confluence with the Lukeni River, Kutu Territory , 02 48 ' 35.2 '' S, 018 11 ' 09.3 '' E, July 25, 2022, R. Monsembula; AMNH 278165 (2), 68.1–70.4 mm SL, in a tributary of Ndzaa River over mud and vegetal debris, in forest habitat , in about 6.3 km upstream of the Ndzaa confluence with the Lukeni River, Kutu Territory , 02 54 ' 58.5 '' S, 018 10 ' 59.9 '' E, July 24, 2022, R. Monsembula; AUM 86509 (1), 49.8 mm SL, collected with the holotype, M. Y. Modimo, August 10, 2021; MRAC 2024.008.P.0001 (1), 62.55 mm SL, Tshe River (tributary of Mfimi River) in about 5.9 km upstream of Nioki, over mud and vegetal debris, in grass habitat , Kutu Territory , 02 44 ' 42.01 '' S, 017 44 ' 33.87 '' E, August 2015, R. Monsembula et al.; ROM 112355 (2); 61.8–70.8 mm SL, same location as AMNH 278165, July 30, 2023, R. Monsembula; ZSM 48482 (1), 67.5 mm SL, main channel of the Ndzaa River over mud and vegetal debris , in forest habitat , in about 26.2 km upstream of the Ndzaa River confluence with the Lukeni River, Kutu Territory , 02 58 ' 25.08 '' S, 018 07 ' 55.26 '' E, July 25, 2018, fishermen.

3.4.3 | Additional non-type material

AMNH 278167 (12); 38.2–57.4 mm SL, collected with ROM 112355; AMNH 278140 (1), 44.3 mm SL, main channel of the Ndzaa River over mud and plant debris, in forest habitat, 42.2 km upstream of the Ndzaa River confluence with the Lukeni River, Kutu Territory, Mai-Ndombe Province, D. R. Congo, 03 06 ' 10.2 '' S, 018 05 ' 14.1 '' E, M. Y. Modimo, August 13, 2021; AMNH 278169 (1), 34.1 mm SL, collected with the holotype, August 10, 2021, M. Y. Modimo.

3.4.4 | Diagnosis

P. stiassnyae is distinguished from all congeners by having 28–29 vertebrae (vs. 33 or more). P. stiassnyae is also distinguished from all. congeners by the possession of 13–14 pre-anal vertebrae (vs. 15 or more) except for Parauchenoglanis zebratus (14–17) and Parauchenoglanis ngamensis (13, holotype). The new species can further be distinguished from P. cf. punctatus _L3, P. balayi , P. longiceps , P. pantherinus , P. punctatus , and P. ubangensis by a narrower supraoccipital process– nuchal plate interdistance (1.4%–2.9% vs.>3% HL); from P. cf. punctatus _L3, P. guttatus , P. longiceps , P. pantherinus , and P. punctatus by a wider orbital HW (64.7%–76.2% vs. 54.9%–63.9% HL); from P. guttatus , P. longiceps , and P. ubangensis by a wider mouth (37.8%–50.8% vs. 25.9%–35.7% HL); from P. guttatus , P. punctatus , P. ubangensis , and P. zebratus by a wider premaxillary toothplate (12.9%– 18.6% vs. 6.6%–12.5% HL); from P. guttatus , P. longiceps , P. pantherinus , and P. zebratus by a wider head (HW: 70.1%–81.1% vs. 58.9%–69.3% HL); from P. balayi and P. pantherinus by a shorter dorsal-fin spine (10.8%–16% vs. 16.1%–18.8% SL); from P. guttatus and P. pantherinus by a smaller orbital diameter (9.5%–14.2% vs. 14.4%–16.9% HL) and a wider interpectoral distance (16.7%– 21.4% vs. 15.3%–16.6% SL); from P. balayi , P. ngamensis ( holotype), and P. ubangensis by a shorter adipose-fin–caudal-fin interdistance (2.7%–5.2% vs. 6.2%–10.5% SL); and from P. balayi by a longer head (HL: 31.3%–35% vs. 28.1%–30.6% SL) and a narrower interorbital (IOD: 19.5%–27.1% vs. 27.3%–28% HL).

3.4.5 | Description

Based on the holotype and 13 paratypes. General appearance as in Figures 2, 6, and 7 (complete skeleton, external morphology, skull and pectoral girdle, respectively), proportional measurements in Table 3, and meristic counts in Table 4. Small-bodied species (see Figure 6), maximum observed size 73.9 mm SL ( 88.3 mm TL; paratype: AMNH 278137), elongate (SL 4.4–6.4 times maximum body height [MxBH]), somewhat dorsoventrally depressed (MxBH 82.4%–109.5% interpectoral distance [IPcD]). Head depressed (head height [HH] 43.5%– 58.7% HL, orbital head height [OHH] 28.9%–43% HL, and OHH 38.5%–66.1% orbital head width [OHW]) with very depressed snout (snout height [SnH] 18.1%–26.9% HL) and large terminal mouth (37.8%–50.8% HL). Upper jaw prominent with moderately wide premaxillary toothplate (its width 12.9%–18.6% of the HL) comprising two tooth patches. Branchiostegal rays eight or nine. Maxillary and internal mandibular barbels shorter than HL (their length 51.2%– 97.8% HL and 37.2%–77.6% HL, respectively), not surpassing opercular opening. External mandibular barbel generally longer than head (their length 95.4%–147% HL), surpassing tip of adpressed pectoral-fin spine in several specimens. Eye small but not reduced (orbit diameter 9.5%–14.2% HL) and dorsally positioned. Pectoral fin short (length 15.9%–23.1% SL), with seven or eight soft rays, inserted underneath head. Pectoral-fin spine also short (its length 12.9%–18.2% SL) with serrations on both sides. Pelvic fin short with six (one unbranched, five branched) soft rays and generally inserted just posterior to body midline (pre-anal length [PAnL]: 60.3%–72.6% SL). Dorsal fin short (its length 13.3%–18% SL) with two hard and seven soft rays. Dorsal-fin spine also short (10.8%–16% SL), slightly serrated anteriorly, lacking posterior serrations. Caudal fin rounded with 15 or 16 principal rays, including two unbranched. Dorsal surface of neurocranium ornamented with tubercles and with single oblong anterior fontanel. Nuchal plates similarly ornamented on dorsal surface, forming a narrow, anteriorly pointed triangle that surrounds anterior base of dorsal-fin spine (Figure 7a). Anterior bifurcation of mesethmoid narrow, not exceeding posterior mesethmoid width. Infraorbital series present as four narrow cylindrical ossifications. Orbit bordered dorsally by frontal, anteriorly by lateral ethmoid, posteriorly by sphenotic, and ventrally by third and fourth infraorbitals (see Figure 7a). Urohyal trifurcate posteriorly (see Figure 7b). Cleithrum with concave anterior margin and prominent humeral processes. Supraoccipital process narrow and sharply pointed.

(Continues)

T A B L E 3 (Continued)

3.4.6 | Colouration

In preservation, ventral side of the head and body whitish brown to brownish, sometimes with small spots, dorsal side of head and body darker brown. Flanks, head, dorsal fin, and adipose fin with darker brown large spots and light brown vermiculated lines forming a reticulate patterning reminiscent of the distinctive color pattern of the giraffe. Three to four vertical black-dotted bars are visible in some preserved specimens. Dorsal and caudal fins brownish with smaller dark spots. Pectoral, pelvic, and anal fins vary from dark brown to light gray or brown without notable spots. Distal tip of spines (pectoral and dorsal) varies from whitish to light brown, whereas the remaining part (proximal tip) varies from brown to light brown. No live specimens have been examined; however, postmortem pictures taken in the field suggest similar colouration in live specimens.

3.4.7 | Distribution

Currently known only from tributaries of the Mfimi-Lukenie River basin. The holotype, several paratypes, and additional non-type specimens have been collected in the Ndzaa River basin (Figure 1) where the species is widespread. Additional paratypes were collected in the Lobee River (a left-bank tributary of the Mfimi), the Molibampe River at Nioki (right-bank tributary of the Mfimi), and the Tshe River (another right-bank tributary of the Mfimi) upstream of the town of Nioki (Figure 1). However, it should be noted that P. stiassnyae only differs by 2% in COI sequences from specimens collected in the Itimbiri River 730 km northeast of the Mfimi. Additional collecting throughout the Mfimi River system and the Cuvette Central ecoregion, coupled with further molecular and morphological investigation, will likely extend this species range.

3.4.8 | Biology and ecology

Most specimens of P. stiassnyae were collected in forested habitats over mud and plant debris in tributaries of the Mfimi River. The rivers where specimens of P. stiassnyae have been collected are characterized by a humic, moderately acidic (pH 4.1–5.3), and dark-brown water with low conductivity (10–50 μS/cm) and low concentrations of dissolved solids (TDS: 10–30 mg /L). These observations, combined with the species body colouration, suggest that P. stiassnyae is adapted to forested habitats, muddy, humic, and dark-brown waters of the Mfimi River tributaries.

3.4.9 | Etymology

P. stiassnyae is named after Melanie L. J. Stiassny (MLJS) of the AMHN. MLJS is the initiator of the AMNH Congo Project that resulted in significant documentation and an improved systematic, biological, and evolutionary understanding of the Congo River basin ichthyofauna with an extensive collection deposited at the AMNH, the University of Kinshasa, and the University of Marien Ngouabi. Additionally, MLJS trained and continues to train numerous Congolese ichthyologists, including the authors of the present paper. We dedicate this species to her outstanding work and commitment to biodiscovery and conservation in the Congo River basin.

3.4.10 | Material examined

P. balayi Sauvage 1879 (AMNH 267139, 2 specimens, 115.1–149.7 mm SL, Mpoukou River, Kouilou-Niari basin, collected by Walsh et al. in November 2013; AMNH 258978, three specimens, 133.4–150.5 mm SL, Louesse River, Kouilou-Niari basin, collected by Walsh et al. in January 2012; AMNH 232082, one specimen, 124.6 mm SL, Ivindo River, Ogooué basin, collected by Lahm in May 2000), four P. guttatus (AMNH 240688, four specimens, 46.7–94.7 mm SL, Ivindo River, Ogooué basin, collected by Lavoué et al. in July 2007), four P. longiceps Boulenger 1913 (AMNH 267131, four specimens, 96.3–119.1 mm SL, Louesse River, Kouilou-Niari basin, collected by Walsh et al. in October 2013), five P. pantherinus Pellegrin 1929 (AMNH 267133, three specimens, 79.2–141.1 mm SL, 267133, Louesse River, Kouilou-Niari basin, collected by Walsh et al. in October 2013; AMNH 258980, one specimen, 119.9 SL, Mandoro River, Ogooué basin, collected by Walsh et al. in January 2012; AMNH 256546, one specimen, 70.3 mm SL, Kessampo River , Ogooué basin, collected by Mamonekene in December 2011), eight P. punctatus (AMNH 244272, two specimens, 153.1–182.1 mm SL, Sangha River , Congo basin, collected by Mamonekene in September 2006; AMNH 227563, two specimens, 113.7–115.7 mm SL, Sangha River , Congo basin, collected by Sullivan et al. in June 1998; AMNH 274626, two specimens, 88.3–130.2 mm SL, Mfimi River , Congo basin, collected by Stiassny et al. in July 2018; AMNH 278134, one specimen, 128.7 mm SL, Ndzaa River , Congo basin, collected by Modimo et al. in August 2021; AMNH 278135, one specimen, 65.2 mm SL, Ndzaa River , Congo basin, collected by Modimo et al. in August 2021), 10 P. cf. punctatus _L3 (AMNH 259229, 2 specimens, 73.9–75.3 mm SL, Mayi Ndombe River , Congo basin, collected by Liyandja et al. in July 2011; AMNH 259275, two specimens, 92.3–95.9 mm SL, Mayi Ndombe River , Congo basin, collected by Liyandja et al. in July 2011; AMNH 268756, one specimen, 71.4 mm SL, Kwango River, Congo basin, collected by Liyandja et al. in January 2016; AMNH 259379, one specimen, 71.4 mm SL, Mayi Ndombe River , Congo basin, collected by Liyandja et al. in September 2011; AMNH 259346, four specimens, 72.8–92.3 mm SL, Mayi Ndombe River , Congo basin, collected by Liyandja et al. in September 2011), and four specimens of P. ubangensis Boulenger 1902 (AMNH 228563, four specimens, 70.7–103.2 mm SL, Ubangi River , Congo basin, collected by Haroun & Albert in July 1998). All from Gabon: N. macrostoma : AMNH 211412 (1, CT-scanned), 180.8 mm SL, Woleu River, Woleu-ogooue, collected by Adriaens et al. in September 2000; AMNH 271727 (1), 154.01 mm SL, Bitoku River, Ngounie, 01 13 ' 57 '' S, 010 35 ' 02.3 '' E, collected by Cutler & Mve Beh in April 2017; AMNH 262942 (1), 115.3 mm SL, Ogooue-Ivindo, 00 29 ' 01.4 '' N, 12 53 ' 33.6 '' E, collected by Cutler et al. in April 2014; AMNH 240697 (1), 85.6 mm SL, Bale Creek , Ogooue-Ivindo, 00 31 ' 08.9 '' N, 12 47 ' 58.1 '' E, collected by Lavoue et al. in July 2007.