SPECIAL ISSUE REGULAR PAPER Review of the cichlid genus Thysochromis (Teleostei: Ovalentaria) with the description of a new species from the Kouilou Province in the Republic of Congo, west–central Africa Gina Walsh 1,3,4 |Anton Lamboj 2 | Melanie L.J. Stiassny 3 1 University of the Witwatersrand, School of Animal Plant and Environmental Sciences, Braamfontein, Johannesburg, South Africa 2 University Vienna, Faculty of Life Sciences, Department for Integrative Zoology, Althahnstrasse 14, Vienna, Austria 3 American Museum of Natural History, Department of Ichthyology, Central Park West at 79th Street, New York, New York, USA 4 Flora Fauna & Man Ecological Services Ltd., Road Town, Tortola, British Virgin Islands Correspondence Gina Walsh, University of the Witwatersrand, School of Animal Plant and Environmental Sciences, Braamfontein, Johannesburg, South Africa, 2000 Email: g.walsh@florafaunaman.com This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/jfb.14144 This article is protected by copyright. All rights reserved. Funding information Initial field studies were part of an environmental impact assessment in the region. Subsequent collection surveys were supported by the University of the Witwatersrand, University Research Council Grant, the National Research Foundation Rated Researchers Incentive Grant 103581 and the Axelrod Curatorship of the American Museum of Natural History. ABSTRACT A new species of the chromidotilapiine genus Thysochromis, is described from the Noumbi and Kouilou River drainages in the Republic of Congo. Based on the current investigation, Thysochromis is resolved as containing two geographically disjunct species, T. ansorgii from localities in the upper Guinean ichthyofaunal province (Ivory Coast, Ghana, Benin and Nigeria) and Thysochromis emili sp. nov. restricted to coastal regions of the Republic of Congo in the lower Guinean province. KEYWORDS lower Guinea, morphology, mtDNA, Thysochromis emili sp. nov., taxonomy 1 | INTRODUCTION This article is protected by copyright. All rights reserved. In a report on the fishes of the lower Kouilou River in the Republic of Congo, Teugels et al. (1991) recorded the presence in Lake Koubambi of two specimens (MRAC 90-57-P-5288-89) of the cichlid Thysochromis ansorgii (Boulenger 1901). They noted that this record represented a significant range extension for a species that was otherwise known only from the upper Guinean ichthyological province in south-eastern Ivory Coast, south-western Ghana, Benin and Nigeria (Figure 1). Later, Lamboj & Stiassny (2007) commented on the questionable composition and taxonomy of the genus, originally named Thysia by Loiselle & Welcomme (1972) but renamed due to preoccupation as Thysochromis by Daget (1988). While the synonymy of Pelmatochromis (Thysochromis) arnoldi Boulenger 1912 with T. ansorgii has generally been accepted (Loiselle & Welcomme, 1972; Fricke et al., 2018), the status of Pelmatochromis (Thysochromis) annectens Boulenger 1913 has remained uncertain (Lamboj, 2004; Froese & Pauly, 2019), as Loiselle & Welcomme (1972) considered the only differences between T. annectens (type locality, lower Niger River) and T. ansorgii (type locality, Ethiop River in Niger Basin) were slight variants of colour patterning. Beyond these they were unable to separate the two and concluded that it was best to accept T. annectens as a species inquirenda (Froese & Pauly, 2019). A fourth species, Tilapia maculifer Ahl 1939 (type locality, Lagos, Nigeria) was synonymised with T. ansorgii by Daget (1991), but unfortunately the holotype and unique specimen, originally housed in the Zoologisches Museum Berlin, is lost and unavailable for study (Fricke et al., 2019). Pending a more detailed review, Lamboj & Stiassny (2007) accepted the identification of This article is protected by copyright. All rights reserved. the two Lake Koubambi specimens as T. ansorgii thereby recognising a range extension for the species of well over 1000 km from the upper Guinean ichthyofaunal province into the southern portion of the lower Guinean province. Walsh et al. (2014) reported on a series of collections made throughout the lower Kouilou, Noumbi and nearby coastal basins where numerous additional samples of Thysochromis spp. were recovered from Lakes Youbi and Yangala. In 2017, G.W. collected additional specimens in both black water (Bondo River, Noumbi Basin) and clear water (Tsissa River, Kouilou Basin) rivers in the same region (Figure 1). Examination of these materials and comparison of the available type materials of the putative West African species, indicates that although phenetically similar, the Republic of Congo specimens are diagnostically distinct from their West African congener and in the current paper we describe the Congolese populations of Thysochromis as a new species. 2 | MATERIALS AND METHODS Collection permits were issued by the National Institute for Research in Exact and Natural Sciences (IRSEN Permit 205 and 328) and CITES permits for exportation are CG1125774 and CG1125818. 2.1 | Field Sampling This article is protected by copyright. All rights reserved. Various lentic (lake and swamp) and lotic (river and stream) habitats were sampled in 2012 and 2017 in the lower Kouilou and Noumbi River basins, as well as in numerous coastal lakes and associated drainages (Figure 1). Fish sampling effort was standardised according to habitat type and fishes collected according to AFS/AIFRB/ASIH (2003) guidelines. Specimens are deposited in the ichthyology collections of the American Museum of Natural History (AMNH) in New York, USA, with all data accessible online (http://sci-web-001.amnh.org/db/emuwebamnh/).. 2.2 | Morphology Twenty-five standard morphometric measurements and 14 meristic counts (Tables 1, 2) were recorded following Barel et al. (1977). Vertebral and fin-ray counts were taken from radiographed or cleared and stained (c&s) specimens. Total gill raker counts for the first arch include the raker at the junction of ceratobranchial and epibranchial elements. Lateral line counts exclude any small pored scales distal to the hypural plate. For detailed anatomical investigation two specimens (T. ansorgii, AMNH 235838 and T. emili sp. nov., AMNH 258135) were scanned using a Phoenix v/tome/x M scanner (GE Measurements and Control; GR Digital; www.ge.com), processed using datos/x software 2.3 and segmented and visualized using VG StudioMax 3.3 (Volume Graphics; www.heidelberg.com). Institutional abbreviations follow Sabaj (2016), LS is standard length and LH, head length. This article is protected by copyright. All rights reserved. The smatr package for (standardised) major axis estimation and testing routines (Warton et al., 2012) was used in RStudio (www.rstudio.com) to calculate allometric coefficients for morphometric data (Sidlauskas et al., 2011; Mipounga et al., 2019). Allometric analyses were factorised using two groups to simultaneously test morphometric similarity between the upper Guinean type materials and dissimilarity between those and lower Guinean specimens. Factor groupings included (1) Thysochromis emili sp. nov. and (2) the type series of T. ansorgii, T. annectens and T. arnoldi. Allometric coefficients for each factor were calculated using standardised major axis regression of natural-log transformed morphometric traits against the natural log of LS. Although morphometric allometries were parallel between species, size-standardised multivariate principal component analysis (PCA) could not be applied due to marked variation in life stage structure amongst samples and limited among-group patterns on PC2–PC5 (Sidlauskas et al., 2011). Bivariate plots from the regressions with parallel allometries and significant offset intercepts (P < 0.05) were used to investigate morphological differences between the upper and lower Guinean samples. 2.3 | Mitochondrial DNA DNA extraction, cytochrome oxidase subunit I gene (coI) amplification and sequencing were undertaken by Inqaba Biotechnical Industries (Pty) Ltd. ()www.inqababiotec.co.za). Contig This article is protected by copyright. All rights reserved. assembly and sequence editing were performed using Geneious 11.1.5. (Kearse et al., 2012) and GenBank accession numbers for the sequences generated in this study are given in Table 3. 2.4 | Habitat Association Abiotic (landscape scale, physico-chemical and qualitative habitat) data were collected at 15 surveyed sites. Fish habitat assessment was undertaken following Kleynhans (2007) to estimate the occurrence of broad fish-habitat cover types in various depth classes. Site slope, average catchment slope, catchment size and stream order were modelled using Shuttle Radar Topography Mission (SRTM) imagery at a 30 m resolution (METI & NASA, 2018) processed in ESRI ArcMap10.5 (www.resources.esri.com). For the purpose of illustrating habitat associations of T. emili sp. nov., abiotic and fish community data were subjected to canonical correspondence analysis (CCA) using Canoco 4.5 (ter Braak & Smilauer, 2002). The CCA was carried out on log-transformed species and environmental data. Forward selection with partial Monte Carlo permutation testing was used to assess the significance of each environmental predictor variable for extending the subset of explanatory variables used in the ordination model. The significance of axes was tested using unrestricted Monte Carlo permutation testing (499 permutations’ P < 0.05). 3 | RESULTS This article is protected by copyright. All rights reserved. 3.1 | Group separation Standardised major axis regressions indicated that the two geographically disjunct groups of specimens differ significantly (P < 0.05) in allometric trajectories of caudal-peduncle length (P < 0.05) and postorbital length (pol) (P < 0.05; Figure 2). Caudal-peduncle length (cpl) showed a weak negative allometry for upper Guinean samples (T. ansorgii group), while lower Guinean samples (T. emili) exhibited a strong positive allometry (0.872 and 1.477, respectively). The postorbital length was weakly positive for the upper Guinean samples (1.129) while the lower Guinean samples showed a weak negative allometry (0.857) Separation of upper and lower Guinean samples is further supported by the degree of sequence divergence in the bar-code coI gene (Table 3) between exemplars from these two regions. These data are represented here as a distance matrix (Figure 3) and divergence between exemplars from the two geographically separated populations exceeds the standard heuristic threshold of 3% commonly used as an indicator of species-level differentiation (Herbert et al., 2003; Arroyave et al., 2019). While exceptions to this heuristic threshold certainly exist (Joyce et al., 2011; van der Walt et al., 2017) these molecular data, taken in combination with the morphometric separation highlighted above and a few qualitative anatomical differences (discussed below), reveal a clear separation between upper and lower Guinean populations. This article is protected by copyright. All rights reserved. Based on these combined data we describe here the lower Guinean populations of Thysochromis as a new species. It is worth noting that a few specimens previously identified as Thysochromis from intervening regions are housed in museum collections. None are reported from Cameroon and the few from Gabon have been examined in the present study. With the single exception of a juvenile collected near Mayumba, in a coastal basin just north of the Kouilou in the Republic of Congo (MRAC A1-88-P-2497, photograph examined), all others are misidenfications of the chromidotilapiine species Chromidotilapia kingsleyae Boulenger 1898 and Divandu albimarginatus Lamboj & Snoeks 2000 (pers. obs). 3.2 | Thysochromis emili sp. nov. Figures 4–5 and Table 1; urn:lsid:zoobank.org:pub:1E60CEA4-3DAE-45b7-AF1204EB6250E9D7. 3.2.1 | Holotype AMNH 271740, male, 69.4 mm LS, Republic of Congo, Kouilou Province, Lake Youbi, 04o 11’ 30.4” S, 11o 40’ 12.8” E, M.N. Jonker, V. Mamonekene, V. Boukaka Mikembi, 17 July 2012. 3.2.2 | Paratypes This article is protected by copyright. All rights reserved. AMNH 271741, 6 specimens, 1 c&s, 55.4–66.7 mm LS, same data as holotype. MRAC 2018027-P-0003-0004, 2 specimens, 60.7–61.2 mm LS., same data as holotype. NMW 99244, 2 specimens, 58.2–62.4 mm LS, same data as holotype. AMNH 271742, 3 specimens, 63.1–67.2 mm LS, Republic of Congo, Kouilou Province, Lake Yangala, 04 o 07’ 26.1” S, 11o 35’ 48.9” E, M.N. Jonker, V. Mamonekene, V. Boukaka Mikembi, 19 July 2012. ZSM 47495, 2 specimens, 63.4–65.0 mm LS, same data as AMNH 271742. AMNH 271747, 2 specimens. 36.0–54.0 mm LS, Republic of Congo, Kouilou Province, Bondo River, 04o 4’ 7.04” S, 11o 38’ 3.08” E, G. Walsh, V. Boukaka Mikembi, J. Mountou, 6 September 2017. AMNH 271748, 1 specimen, 61.0 mm LS, Republic of Congo, Kouilou Province, Tsissa River, 04o 0’ 57.63” S, 11o 42’ 4.09” E, G. Walsh, V. Boukaka Mikembi, J. Mountou, 7 September 2017. 3.2.3 | Differential Diagnosis While no unambiguous morphological autapomorphies have been located to diagnose T. emili sp. nov., it is distinguished from its West African congener, T. ansorgii, by the following combination of characters (Tables 1, 2). Fewer scale rows between the pectoral and pelvic-fin origins (3–4 v. 5–6), jaw teeth closely spaced and evenly implanted over entire length of both upper and lower jaws (v. widely space and unevenly implanted along distal portions) and a supraoccipital crest that is continuous with the frontal ridge (v. terminating posterior to frontal This article is protected by copyright. All rights reserved. ridge). Shorter postorbital length (38.2–41.9% v. 42.8–46.7% LH) and a shorter caudal peduncle length (7.7–11.3% v. 11.4–12.7% LS). 3.2.4 | Description Medium-sized cichlid, maximum recorded LS 91.3 mm (mature male, MRAC 90-57-P-5288; Figure 4). Counts and proportional measurements for holotype and 18 paratypes given in Table 1. Deep-bodied (body depth, DB 38.4–47.8% LS), greatest depth at level of 4th or 5th dorsal-fin spine. Head small (LH 34.2–38.9% LS, depth 65.0–76.8% LH), short postorbital length (38.2– 41.9% LH), snout short, mouth small with well-developed, fleshy lips. Dorsal head profile 40– 50° to mid-orbit, rising steeply to nape. Dorsal and ventral body profiles convex to short (7.7– 11.3% LS), deep (15.6–18.5% LS) caudal peduncle. Dorsal fin XV–XVII (mode XVI) 9–11 (mode 10). Anal fin III 7–9 (mode 8). Dorsal spines increase in length posteriorly. Soft dorsal and anal fins extending over caudal-fin base. Caudal fin large, sub-truncate to rounded, with 14 branched rays. Pectoral fins short and rounded, extending to mid-body, not reaching anus. Pelvic fins reaching just short of, or to anus in females, extending beyond anal-fin origin in mature males. First branched ray of pelvic fin longest in both sexes. Jaws short and isognathus. Outer row teeth in both jaws, somewhat recurved unicuspids, with distally flattened, bilaterally shouldered crowns (Figure 5a). Outer row premaxillary and dentary This article is protected by copyright. All rights reserved. teeth evenly implanted, closely spaced over entire length of dentigerous arms (Figure 5a) v. widely spaced and unevenly implanted along distal portions in T. ansorgii (Figure 5b). Two to four inner rows of small, similarly shaped, unicuspid teeth restricted to anterior third of both jaws. Infraorbital series with broad, plate-like first infraorbital (lachrymal) bearing 4 small, sensory-canal pores. Second to fifth infraorbital elements narrow and tubular, forming complete suborbital ring. Lower pharyngeal jaw wider than long, with slightly convoluted ventral suture. Twenty-four to 28 teeth along posterior row, symphysial teeth moderately robust, becoming slender laterally. Eight to ten tuberculate ceratobranchial rakers along first arch, often short raker in angle of arch, 4–7 simple epibranchial rakers. Microbranchiospines lacking on inner faces of second to fourth arches. Pharyngeal hanging pad moderately developed, extending just anterior to first epibranchial. Scales cycloid. Flank scales large, uniformly sized onto chest, 3–4 between pectoral and pelvic-fin origins. Cheek with 3 scale rows, 4 horizontal scale rows on opercle. Prominent dark opercular blotch unscaled. Pored lateral-line scales 26–28, upper and lower lateral lines not overlapping. Upper line separated from dorsal-fin base at highest point (8th pored scale) by 2-2.5 scales, last pored scale separated by 1-1.5. Proximal third of caudal fin covered with small interradial scales. Sixteen (rarely 15) circumpeduncular scales. Total number of vertebrae: 24– 26, comprising 13 abdominal and 11–13 caudal centra. This article is protected by copyright. All rights reserved. Supraoccipital crest contiguous with frontal ridge (Fig 5a) v. crest terminating posterior to frontal ridge (Figure 5b). 3.2.5 | Coloration in life Head and body yellowish or yellowish-brown, paler ventrally (Figure 6). Scaleless, dark opercular spot often extending posteriorly over one or two scale rows. Three short dark bars along mid-flank, not extending to ventrum. Single dark bar or rounded spot in midline or over dorsal half of caudal peduncle. Flank scales ringed with dark-brown pigment contrasting with paler central field, more strongly marked in males (Figure 6a) than females (Figure 6b). Ventral portions of cheek, operculum and chest silvery with a greenish or turquoise flush. Cluster of silvery scales located lateroventrally around vent, reduced in number and less clearly marked in males (Figure 6a), prominent in mature females (Figure 6b). Belly flushed pale rosy pink in mature females. Leading edge of pelvic fin darkly pigmented. Soft dorsal and anal fins with alternating pale and dark maculae variously evident, but always present. Caudal-fin membranes with conspicuous rows of maculae, strongest proximally. All fin spotting more prominent in mature males than in females and juveniles. In preservation (Figure 4), ground coloration of body brownish yellow, darker dorsally. Opercular spot and bars on flank and caudal peduncle clearly visible, fin maculae variously evident. This article is protected by copyright. All rights reserved. 3.2.6 | Distribution Despite extensive collections made during a number of surveys throughout the region, T. emili sp. nov.is known from only five localities (Figure 1). Currently it has been recorded in the Noumbi and Kouilou River drainages in the Republic of Congo and appears to be restricted to larger systems in the coastal plain of the Republic of Congo. The species has been recorded from Lakes Youbi, Yangala and Koubambi and in the Bondo and Tsissa Rivers. The record of T. emili in Lake Koubambi is based on specimens collected by Teugels et al. (1991), but despite extensive sampling of suitable habitat in that lake during the 2012 and 2017 expeditions, the species was not re-collected there. Vreven et al. (2007) recorded multiple introductions of the Nilo-Sudanic species, Heterotis niloticus (Cuvier 1829), throughout the region and Walsh et al. (2014) reported on the dominance of H. niloticus in catches from Lake Koubambi. We suggest that the current absence, or rarity, of T. emili sp. nov. in Lake Koubambi may be the result of competition with introduced H. niloticus for habitat and resource partitions. As noted above, examination of a photograph of a single juvenile Thysochromis specimen (MRAC A1-88-P-2497, specimen lost) from a coastal basin just north of the Kouilou, in Gabon, suggests that the distribution of T. emili sp. nov. probably extends into suitable habitats in southern coastal Gabon. 3.2.7 | Habitat Preferences This article is protected by copyright. All rights reserved. The species–environment correlations showed a cumulative percentage variance of species data of 49.1% explained on the first two axes. Environmental variables significantly (P ≤ 0.05) contributing towards the measured variance in the data include catchment size (P < 0.01) conductivity (P < 0.01), turbidity (P < 0.01), stream order (P < 0.01) and aquatic macrophytes (P < 0.05; Figure 7). Thysochromis emili sp. nov. were collected exclusively in well oxygenated lakes and rivers situated in higher order systems (> 4th order) of the Kouilou and Noumbi River basins. The species was sampled over sandy substrate in shallow (< 0.5 m), clear, shoreline waters fringed by abundant overhanging vegetation, deeply undercut banks and root wads. It was not found in other coastal lake or river basins despite efforts to collect it in these localities. The new species showed a positive correlation and co-occurrence with the distichodontid Nannocharax parvus Pellegrin 1906 and two other omnivorous or herbivorous substrate-brooding cichlids Coptodon guineensis (Günther 1862) and Coptodon tholloni (Sauvage 1884). 3.2.8 | Breeding Behaviour Not known, but as compared with its west African congener and its preferred habitat, it is probably a pair-bonding, cave brooder. This article is protected by copyright. All rights reserved. 3.2.9 | Etymology The species is named for Emil Woolf Kentridge-Young, grandson of William Kentridge and Anne Stanwix, in recognition of their support of research in Africa. 3.3 | Additional Material Examined AMNH 258106, 12 specimens, Republic of Congo, Kouilou Province, Lake Youbi, 04o 11’ 30.4” S, 11 o 40’ 12.8” E, M.N. Jonker, V. Mamonekene, V. Boukaka Mikembi, 17 July 2012. AMNH 258135, 8 specimens, 1 c&s, Republic of Congo, Kouilou Province, Lake Yangala, 04 o 07’ 26.1” S, 11o 35’ 48.9” E, M.N. Jonker, V. Mamonekene, V. Boukaka Mikembi, 19 July 2012. AMNH 261035, 2 specimens, Republic of Congo, Kouilou Province, Lake Yangala, 04 o 07’ 26.1” S, 11o 35’ 48.9”, Mamonekene and Walsh, 19 July 2012. MRAC 90-57-P-5288-89, 2 specimens, Republic of Congo, Kouilou Province, Lake Koubambi, G. Teugels et al., 1990. MRAC A1-088-P-2497, 1 specimen (photograph examined), Gabon, Petit ruisseau sur route forestière aprés Doumvou, Mamonekene, 24 July 2001. 3.4 | Comparative material examined 3.4.1 | Thysochromis annectens This article is protected by copyright. All rights reserved. BMNH 1913.7.15:8–9, syntypes, 2 specimens, 52.8–83.4 mm LS, Nigeria, Lower Niger River, J.P. Arnold. 3.4.2 | Thysochromis arnoldi BMNH 1912.2.2:10–12, syntypes of T. arnoldi, 3 specimens, 56.1–65.4 mm LS, Nigeria, lower Niger River, J.P. Arnold. 3.4.3 | Thysochromis ansorgii BMNH 1901.1.28:9–12, syntypes, 4 specimens, 40.7–67.5 mm LS, Nigeria, Niger River system, Ethiop River at Sapele station, W.J. Ansorge.–MRAC 91-10-P-661–671, 11 specimens, 35.8– 54.0 mm LS, Nigeria, Niger River system, New Calabar River, Akpor, C.B. Powell, December 1990.–AMNH 225991, 2 specimens, 1 c&s, 54.5–61.5 mm LS, Nigeria, New Calabar River system, stream 3 km southeast of Emuhoa, C.B. Powell, 5 January 1991.–AMNH 235838, 2 specimens, 1 c&s, 62.9–71.6 mm LS, Benin, Oueme River, small stream near game village, R. Schelly et al., 13 November 2003. 4 | DISCUSSION This article is protected by copyright. All rights reserved. Lamboj & Stiassny (2007) accepted the identification of Teugels et al. (1991) for two specimens from Lake Koubambi in the Republic of Congo as T. ansorgii thereby recognizing a 1000+ km range extension spanning two ichthyofaunal regions. However, based on the current study, Thysochromis is resolved as containing two geographically disjunct species: T. ansorgii (including T. annectens and T. arnoldi as synonyms) from the upper Guinean ichthyofaunal province and T. emili sp. nov. restricted to the lower Guinean province, specifically the Kouilou Department of the Republic of Congo. The Kouilou Department is located along the Atlantic coastal plain in the southern portion of the lower Guinean ichthyofaunal province. The region consists of low-altitude savanna and forest ranging between Gabon to the north and Cabinda to the south (van Rooyen et al., 2016; FEOW, 2019). The lowland coastal area has a continuum of beaches and dunes in the west, transitioning into undulating hills on the coastal plains and the Mayumbe Escarpment in the east. The landscape is crossed by a dense network of drainage channels flowing into larger rivers and natural lakes, resulting in a high freshwater habitat heterogeneity (Vande Weghe, 2004; Walsh et al., 2014; van Rooyen et al., 2016). The high richness in freshwater fish in the lower Guinean province (Stiassny et al., 2007) was probably driven by the aquatic refugium offered by the forested west coast equatorial region during climatic fluctuations during the Pleistocene (Lévêque, 1997; Brooks et al., 2011). It appears that the lower and upper Guinean ichthyological provinces have more recently experienced recurrent isolation during dry phases of the climatic cycle that reduced the rainforest between the Late This article is protected by copyright. All rights reserved. Pleistocene and present day and which created optimal conditions for allopatric speciation (Teugels et al., 1991; Lévêque, 1997). The current study highlights the importance of including multiple data sources when considering geographically widespread and taxonomically under-studied species where failure to recognize divergent lineages has often resulted in the underestimation of diversity (Arroyave et al., 2019). ACKNOWLEDGEMENTS Our thanks to J. Snoeks and M. Parrent (MRAC), J. Maclaine (BMNH) and M. Hakansson (Gothenburg, Sweden) for the donation or loan of materials. We thank J.Y. Gaugris (Flora Fauna and Man Ecological Services), V. Mamonekene and V.N. Boukaka Mikembi (University of Marien Ngouabi, Republic of Congo) and M.N Jonker (Ecotone Freshwater Consultants) for facilitation and participation of expeditions in the region. L. Kirtley, L. Passy and K. Wheeler (Elemental Minerals) for logistical support in the field. We gratefully acknowledge B. Sidlauskas (Oregon State University) and anonymous reviewers who gave input that improved the quality of this paper. Finally, we thank Jean de Dieu Mountou, Frédéric Avoukou and Gislain Nakoundzi Taty of Koutou Village for their invaluable assistance during our field collections. Author Contributions This article is protected by copyright. All rights reserved. G.W. designed field surveys, collected fish specimens and environmental data and performed statistical computations. A..L performed morphometric and meristic analyses and M.L.J.S. was responsible for CT scanning, qualitative morphological analysis and DNA analysis. All authors contributed to the writing of the manuscript. 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I., Duursma, R. A., Falster, D. S., & Taskinen, S. (2012) SMATR 3– an R package for estimation and inference about allometric lines. Methods in Ecology and Evolution, 3, 257–259. This article is protected by copyright. All rights reserved. SIGNIFICANCE STATEMENT The composition and taxonomy of the genus Thysochromis Daget 1988 has long been considered problematical and in need of revision. This study clarifies the composition of the genus, synonymizing three described Upper Guinean species, and includes a description of a new species of the chromidotilapiine cichlid genus from the lower Kouilou and Noumbi basins of southern Republic of Congo in the Lower Guinean ichthyofaunal province. This article is protected by copyright. All rights reserved. Accepted Article CAPTIONS TO FIGURES FIGURE 1 (a) Distribution of Thysochromis ansorgii (■→) and Thysochromis emili sp. nov. (■→★). (b) Typical habitat in Lake Youbi and (c) in Tsissa River where T. emili were collected Typesetter 1 Change A, B etc to (a), (b) etc. 2 Delete E and s from lat and long values. FIGURE 2 Standardised major axis regressions of the natural log of (a) caudal peduncle length (cpl), and (b) postorbital length (pol) against the natural log of standard length (LS) for: ●, Thysochromis emili sp. nov.; ▲, T. ansorgii; ♦, T. arnoldi; ■, T. annectens. █, Area of 95% CI Typesetter 1 Configure as shown, with tick marks aligned on numerical values. 2 If possible, deete background shading. This article is protected by copyright. All rights reserved. Accepted Article FIGURE 3 Matrix of cytochrome oxidase subunit I gene (coI) distance between Thysochromis emili sp. nov. and T. ansorgii from different locations. Inset images are of voucher specimens photographed immediately post mortem Typesetter 1 Delete n. sp. 2 Delete grid lines FIGURE 4 (a) Lateral view of preserved male Thysochromis emili sp. nov. general habitus (holotype, AMNH 271740) and (b) female (paratype, AMNH 271742). Scale bar = 1 cm Typesetter 1 Change A, B to (a), (b). FIGURE 5 Whole specimen and microCT scanned lateral views of neurocranium and premaxilla, of (a) Thysochromis emili sp. nov. (AMNH 258135) and (b) Thysochromis ansorgii (AMNH 235838). Scale bar = 3 mm Typesetter 1 Change A, B to (a), (b). FIGURE 6 Immediately post mortem coloration of Thysochromis emili sp. nov.. (a) male from Lake Youbi and (b) female from Lake Yangala Typesetter 1 Change A, B to (a), (b). This article is protected by copyright. All rights reserved. Accepted Article 2 Delete E and s from lat and long values. FIGURE 7 Canonical correspondence analysis of the fish community data in relation to various environmental attributes. ← and bold text, abiotic variables; ▼, position of Thysochromis emili sp. nov. This article is protected by copyright. All rights reserved. Accepted Article TABLE 1 Morphometric measurements and meristic data for the holotype and 18 paratypes of Thysochromis emili sp. nov. Morphometric measurements Standard length (LS; mm) % LS Head length (LH) Body depth Caudal-peduncle length Caudal-peduncle depth Dorsal-fin base Anal-fin base Predorsal length Pre-anal length Prepectoral length Prepelvic length Longest dorsal-fin ray Longest anal-fin ray Longest pectoral-fin ray Longest pelvic-fin ray % LH Head depth Snout length Eye diameter Postorbital length Interorbital distance Cheek depth Premaxillary length Lower jaw length Preorbital length Meristic counts Lateral line scales (upper row) Lateral line scales (lower row) Lateral line scales (total) Circumpeduncular scales Dorsal-fin spine Dorsal-fin rays Anal-fin spine Anal-fin rays Pectoral-fin rays Gill rakers (lower limb) Holotype 69.4 Paratypes min max 36.0 69.4 n mean SD 18 35.9 38.4 10.9 15.8 61.7 21.2 30.1 69.0 37.0 40.7 19.4 23.2 23.1 35.7 34.2 38.4 7.7 15.6 58.0 18.6 29.7 69.0 36.7 40.7 15.6 15.6 22.6 29.7 38.9 47.8 11.3 18.5 62.7 21.3 34.3 75.8 41.0 47.0 26.6 23.8 26.3 37.8 18 18 18 18 18 18 18 18 18 18 18 18 18 18 36.8 43.4 9.9 17.4 60.4 19.4 31.9 73.6 38.8 43.6 19.2 24.4 24.2 31.5 1.4 2.4 1 1 1.4 0.8 1.5 1.8 1.2 1.7 1.8 2.2 2.1 2 69.4 31.0 31.0 40.0 27.6 28.5 28.2 33.9 19.2 Holotype 65 76.8 28.8 34.6 27.0 30.1 38.2 41.9 25.4 33.2 26.2 31.2 23.1 28.2 30.2 38.1 17.2 24 Paratypes 18 18 18 18 18 18 18 18 18 68.7 31.2 28.6 40.2 29.1 29.4 26.1 32.3 20.3 3.2 1.6 1.1 1.1 2.3 1.8 1.9 2.2 1.7 19 7 28 16 XVI 10 III 9 13 9 17(2), 18(2), 19(9), 20(1) 6(1), 7(9), 8(2), 9(1) 26(2), 27(10), 28(2) 15(1), 16(13) XV(6), XVI(7), XVII(1) 9(2), 10(10), 11(3) III(14) 7(1), 8(12), 9(1) 13(14) 8(2), 9(8), 10(4) This article is protected by copyright. All rights reserved. Accepted Article Total gill rakers Abdominal vertebrae Caudal vertebrae Total vertebrae 14 13 13 26 14(3), 15(8), 16(2), 17(1) 13(14) 11(1), 12(110), 13(3) 24(1), 25(9), 26(4) TABLE 2 Morphometric measurements and meristic data for the syntypes Thysochromis ansorgii, T. annectens and T. arnoldi T. ansorgii BMNH 1901.1.28:9–12 Morphometric measurements Standard length (LS; mm) % LS Head length (LH) Body depth Caudal peduncle length Caudal peduncle depth Dorsal-fin base Anal-fin base Predorsal length Preanal length Prepectoral length Prepelvic length Longest dorsal fin-ray Longest anal fin-ray Longest pectoral fin-ray Longest pelvic fin-ray % LH Head depth Snout length Eye diameter Postorbital length Interorbital width min max mean 40.7 67.5 Syntypes T. annectens BMNH 1913.7.15:8–9 min max 63.6 52.8 mean T. arnoldi BMNH 1912.2.2:10–12 min max 56.1 65.4 mean 31.7 43.1 11.4 16.8 60.5 18.6 26.5 69 33.8 37.9 17.8 22.1 22.9 29.4 33.3 46.0 12.7 17.4 64.5 20.1 29.3 72.1 38.2 40.7 25.9 23.8 39.1 33.3 33.1 44.1 12.3 17.2 62.0 18.9 28.7 69.4 35.9 40.2 21.1 22.7 29.7 31.4 35.1 38.2 11.6 16.1 60.2 19.4 30.7 69.4 36.8 42.4 23.1 24.4 27.0 38.8 37.7 37.1 13.8 17.5 60.1 19.2 31.6 68.2 38 42.4 18.6 20.2 25.6 26.7 36.4 37.7 12.7 16.8 60.2 19.3 31.2 68.8 37.4 42.4 20.9 22.3 26.3 32.8 34.0 35.8 12.5 16.1 58.4 19.9 26.2 65.4 34.6 38.5 26.1 31.4 24.6 25.0 35.6 39.9 13.3 17.5 63.9 21.3 31.0 68.6 38.3 40.6 26.6 28.4 30.7 44.5 34.9 37.9 12.8 15.5 60.9 20.5 28.7 66.8 35.9 39.5 24.1 29.8 27.7 33.3 63.1 24.2 25.8 42.8 28.5 71.6 30.6 33.0 46.7 32.6 64.0 27.1 29.5 43.5 30.7 60.9 26.5 27.4 43.5 27.6 65.0 29.2 29.3 44.2 29.4 63.0 27.9 28.4 43.9 28.5 70.7 25.4 24.5 41.3 27.1 78.7 30.1 28.9 47.2 30.1 75.5 28.5 27.0 44.6 28.8 This article is protected by copyright. All rights reserved. Accepted Article Cheek depth Premaxillary length Lower jaw length Preorbital length Meristic counts 31.0 25.3 28.5 18.4 33.2 29.2 34.1 19.6 31.8 27.0 30.7 18.9 Lateral line scales (upper row) Lateral line scales (lower row) 18(1), 19(2) 6(1), 7(3) 26(1), 27(1), 28 Lateral line scales (total) (1) Circumpeduncular scales 16(4) Dorsal-fin spines XV(2), XVI(2) Dorsal-fin rays 10(3), 11(1) Anal-fin spines III(4) Anal-fin rays 7(1), 8(3) Pectoral-fin rays 12 (2), 13(2) Gill rakers (lower limb) 9(3), 10(1) Total gill rakers 13(3), 14(1) BMNH, British Museum (Natural History) 27.7 27.2 29.9 16.9 30.0 29.2 31.3 17.2 28.6 28.2 30.6 17.1 25.7 28.9 33.1 17.0 33.8 33.4 34.4 18.8 31.0 30.8 33.8 17.8 18(1), 19(1) 7(1), 8(1) 19(3) 7(2), 8(1) 26(1), 27(1) 27(1), 28(2) 16(2) XV(2) 9(1), 10(1) III(2) 7(1), 8(1) 13(2) 10(2) 15(1), 16(1) 16(3) XV(1), XVI(2) 9(1), 10(2) III(3) 8(1), 9(2) 13(3) 9(3) 12(1), 13(2) TABLE 3 Taxa, voucher catalog numbers and GenBank accession numbers for coI sequences obtained in this study Taxon AMNH catalogue Tissue code GenBa nk Locality Thysochromis emili sp. nov. AMNH 258106 AMCC 211381 MN160 147 Lake Youbi, Republic of Congo Thysochromis emili sp. nov. AMNH 258135 AMCC 211386 MN160 148 Lake Yangala, Republic of Congo Thysochromis ansorgii ZCUV 2018/003 NIG-001 MN160 149 Niger River, Nigeria Thysochromis ansorgii Uncatalogued photo voucher NIG-002 MN160 150 Niger River, Nigeria AMNH, American Museum of Natural History This article is protected by copyright. All rights reserved. cepted Arti Figure 1 This article is protected by copyright. All rights reserved. Click here to access/download;Figure;Fig. 2A cpl allometry.tiff Accepted Article Figure 2A This article is protected by copyright. All rights reserved. Click here to access/download;Figure;Fig. 2B pol allometry.tiff Accepted Article Figure 2B This article is protected by copyright. All rights reserved. ted Figure 3 This article is protected by copyright. All rights reserved. pted Ar Figure 4 This article is protected by copyright. All rights reserved. ted Figure 5 This article is protected by copyright. All rights reserved. ccepted Artic Figure 7 This article is protected by copyright. All rights reserved. epted Art Figure 6 This article is protected by copyright. All rights reserved.