A collection of fishes from tributaries of the lower Kouilou , Noumbi and smaller coastal basin systems , Republic of the Congo , Lower Guinea , west-central Africa

A list of fishes is reported from right bank tributaries of the lower Kouilou River, left bank tributaries of the Noumbi River, and a series of independent coastal catchments near Madingo-Kayes in the Kouilou Province of the Republic of Congo. Thirty-two sites were sampled in a variety of aquatic habitats in the wet and dry seasons of 2012. Fifty-five fish species distributed in 29 families were collected, three of which represent putatively undescribed species. The most diverse families in the study region were the Cichlidae and the Mormyridae. This paper provides a comparison and update to earlier species lists reported for the general area and offers a baseline that may be used as a point of departure for future ichthyological assessments.


Introduction
The study region (Figure 1) is located northwest of Pointe-Noire in the Republic of Congo and forms part of the Ogooue-Nyanga-Kouilou-Niari Freshwater ecoregion in the Lower Guinean ichthyofaunal province (FEOW 2012;Stiassny et al. 2007).More locally, the survey encompasses an area draining southeast to the Kouilou River, northwest to the Noumbi River and southwest into a series of smaller independent coastal basins.
Rivers in the region experience a bimodal flood regime, where the first flood period occurs in November and the second in April, with little or no rain falling between June and August.The largest river draining the region is the Kouilou which becomes a low gradient system below Sounda Gorge, meandering through dense forest before emptying into the Atlantic Ocean.The aquatic ecosystems of this ecoregion are considered to be notably rich in freshwater species that show high levels of endemicity and considerable habitat heterogeneity, encompassing a wide range of lentic and lotic habitats (Brooks et al. 2011).
Many systems in the ecoregion remain to be sampled, and this is particularly the case for the small coastal basins (Daget and Stauch 1968;Teugels et al. 1991;Mamonekene and Teugels 1993;FEOW 2012).Additionally, very little information is available on the life history, distribution and ecology of freshwater species in this entire region (Mamonekene and Stiassny, 2012).Whilst ichthyological information for the Republic of Congo is generally fragmented and sparse, collections in the lower Kouilou River were made in the early 1960's (Daget 1961) and were later reported by Daget and Stauch (1968).That study reported 61 species from Sounda Gorge to the Kouilou estuary some 75 km downstream (Figure 1).A more recent study was undertaken by Teugels et al. (1991) Abstract: A list of fishes is reported from right bank tributaries of the lower Kouilou River, left bank tributaries of the Noumbi River, and a series of independent coastal catchments near Madingo-Kayes in the Kouilou Province of the Republic of Congo.Thirty-two sites were sampled in a variety of aquatic habitats in the wet and dry seasons of 2012.Fifty-five fish species distributed in 29 families were collected, three of which represent putatively undescribed species.The most diverse families in the study region were the Cichlidae and the Mormyridae.This paper provides a comparison and update to earlier species lists reported for the general area and offers a baseline that may be used as a point of departure for future ichthyological assessments.Coastal savannah streams occur in the southern section of the study area in the savannah region and drain coastal catchments (Figure 2B).These streams have a distinct channel and riparian fringe, moderate depth (< 2 m) and width (1-10 m), and a reduced gradient.Coastal savannah streams have partially open to open canopies and are mostly sandy with marginal vegetation as dominant cover.The sites were fringed by a forest-wetland-grassland mosaic.
Rivers are major drainages consisting of an open canopy, a defined channel and an undefined riparian zone (Figure 2C).They are deep (> 2 m) and wide (> 10 m) with a moderate water velocity.Sampled river sites in this study consisted of affluents of the Kouilou River with seasonally flooded riparian forest characterised species such as Kigelia africana, Entada mannii, Mucuna flagellipes and Raphia hookeri.Increased inundation during the wet season creates flooded forests in the region comprised of species such as the stilt rooted Xylopia rubescens, Aman trobilacea and Ctenolophon englerianus.
Swamp forests are low energy systems where the water table is near to or at the surface (Figure 2D).They are characterised by undefined channels, closed canopies and slow flowing water running through dense vegetation.Swamp forests have a low gradient with water surface width ranging from 1-10 m and a macro-channel width of > 100 m.Leaf litter and debris are the dominant substrate in these systems.Similar to swamp forests, savannah wetlands are low energy systems where the water table is shallow (Figure 2E).Savannah wetlands are characterised by slow flowing, shallow waters without woody vegetation.
They have an open canopy and are dominated by grasses, sedges and forbs.Savannah wetlands cover a large area with disperse flows (> 100 m), but have relatively narrow active channels (1-5 m).
Lakes are standing water bodies located throughout the landscape with a large variability in the surrounding vegetation (e.g., Figure 2F).They are relatively deep (3-8 m) and have a water surface width of 100 m or more with clear waters and open canopies.Estuaries (Figure 2G) and mangrove (Figure 2H) sites were situated in the sublittoral zone.The latter contained saline woodland elements in their adjacent aquatic zones.

Sampling and Collection
Fish sampling efforts were site specific and based on habitat type and accessibility.Several sampling techniques were employed, including cast nets (Figure 3A), fyke nets (Figure 3B), monofilament gill nests (Figure 3C), seine nets (Figure 3D), electrofishing (Figure 3E), dip nets (Figure 3F), hook and line (Figure 3G) and observation of local fishermen's catch (Figure 3H).Fishes were collected according to the guidelines for the use of fishes in research (AFS/AIFRB/ASIH 2003).Taxonomic nomenclature follows Eschmeyer (2010).Some species were observed in the field but not collected, and were only reported if a strong positive identification could be made of the specimen in the field.All vouchers were deposited in the Ichthyology Department of the American Museum of Natural History (AMNH) in New York, USA.Data are accessible online at the AMNH vertebrate zoology database http://sciweb-001.amnh.org/db/emuwebamnh/.Tissue samples for DNA analysis were taken for vouchers.All fishes were collected and exported with permission of the Congolese

Results and Discussion
For the present study a total of 55 species, distributed in 29 families and 12 orders are represented in Table 2, with their distribution amongst habitat types in the local study area indicated.Of the 55 species noted in the study, 42 are considered as primary freshwater species.The families with highest species richness were the Cichlidae (9 spp., 16%), Mormyridae (5 spp., 9%), Clariidae (4 spp., 7%), Distichodontidae (3 spp., 6%) and Nothobranchiidae (3 spp., 6%).The remainder of the 24 families were comprised of one or two species each.The most diverse orders were Perciformes (19 spp., 35%), Siluriformes (9 spp., 17%) and Characiformes (7 spp., 13%), many of the remaining orders were represented by a single species.
In the study area 29 species (54%) were collected in forest streams; 24 species (44%) in lakes, 18 species (33%) in rivers, 8 species (15%) in swamp forests, 7 species (13%) in coastal savannah streams, 4 species in savannah wetlands and estuaries respectively (7%) and 3 species in mangroves (6%).Where previous studies focused mainly on the main rivers, major affluents and lakes in a larger geographic area (Daget and Stauch 1968;Teugels et al. 1991), the current study intensely sampled a smaller area on the catchment divide between the Kouilou and Noumbi near the coast and included numerous smaller tributaries on the right bank of the lower Kouilou River.The low diversity recorded in the coastal savannah streams, savannah wetlands and mangroves is likely an artefact of limited sampling in these habitat types.
Forest streams and rivers exhibited a notable number of fishes that were sampled in these habitats exclusively.Lakes and estuaries showed a lower number of exclusive species, where the remainder of the habitat   The discoveries of three taxa that appear to represent putatively undescribed species are noted in Table 2 and Figure 4. Specimens tentatively identified as A. cf.spilauchen (Figure 4A) were collected near the mouth of the Kouilou River and require further taxonomic elucidation (van der Zee 2013, pers.comm.).Thysochromis ansorgii has previously been recorded by Teugels et al. (1991) in Lake Koubambi and the presence of this species was considered as a significant southerly range extension from its previously recorded localities in the coastal basins in the south of Côte d'Ivoire, south western Ghana and Nigeria.Preliminary examination of Thysochromis specimens collected from Lake Youbi (Figure 4B) and Lake Yangala in the current study reveal obvious differences with T. ansorgii and these specimens are considered as member of a putatively undescribed species (Stiassny 2013, pers. comm.).Marcusenius cf.friteli (Figure 4C) potentially also represents an undescribed taxon (Sullivan 2013, pers.comm.), and the variation in a group of M. moorii sampled at lake Tchitombi is particularly striking (Figure 4C and D).
The occurrence of the mochokid catfish, S. batesii and the clariid catfish Clarias pachynema represents a range extension for these species and is the first record of the species for the Kouilou system.Prior to the present study S. batesii had been recorded in the Lower Guinea in the Nyong and Ntem Rivers (Cameroon), the Ivindo, Ogowe and Ouzibi rivers (Gabon) and the Rio Muni Equatorial Guinea, where C. pachynema was recorded in the Sanaga (Cameroon), Ogowe and Oeme (Benin) systems (Stiassny et al. 2007;Moelants 2010).
A large portion of the biomass of the area was made up of just three species, the alestid Bryconalestes longipinnis, the mormyrid M. moorii and the cichlid Hemichromis elongatus.Hemichromis elongatus was particularly prolific, occurring in large abundances in most habitats sampled and exploiting both brackish and freshwaters (Table 2).
The species-rich Cyprinidae, which represents a large portion of fish diversity in central Africa (Brooks et al. 2011), is represented by only a single species, 'B'.holotaenia, in the study area.Twenty cyprinid species, including representatives of 'Barbus', Garra, Labeo, Labeobarbus, Raiamas and Varicorhinus were recorded in previous collections (Daget and Stauch 1968;Teugels et al. 1991;Stiassny et al. 2007) and nearby regions (Mamonekene and Stiassny 2012).Interestingly most cyprinid species in the region appear to be restricted to the Ntombo River (a major left bank affluent of the Kouilou), the Loeme River, and the Kouilou River and affluents between Kakamoeka and Sounda Gorge north east of the study area.
Fishermen were observed collecting Heterotis niloticus and Parachanna sp. in many of the lakes and in the lagoon.Vreven et al. (2007) reviewed the timeframe of introductions of alien species into the Lower Guinean ichthyofaunal province and noted multiple introductions of H. niloticus throughout the region.Heterotis niloticus has a Nilo-Sudanic origin and it is speculated that it was introduced to the coastal region after the mid sixties, as it was not yet reported by Daget and Stauch (1968) who made their collections between 1962 and 1964.Welcomme (1988) reported the introduction of H. niloticus in the Congo from Cameroon in 1950, but was not specific about the area to which they were introduced.According to local fishermen, the introduction of this species has coincided with the local decline and extinction of other species (Teugels et al. 1991).
When combining data from all studies (Daget and Stauch 1968;Teugels et al. 1991;Stiassny et al. 2007) a total of 152 species in 39 families and 14 orders were recorded for the lower Kouilou, Noumbi and independent coastal basins (Table 3).This tally includes sites on major left and right bank affluents of the Kouilou River up to Sounda Gorge near Kakamoeka.After a review of the available data it appears that identification of several species cited by Daget & Stauch (1968) are unclear and require clarification, specifically for the Nothobranchiidae and the Clariidae families, and for the cichlid species Hemichromis fasciatus.Epiplatys sexfasciatus is restricted to the Ogowe system, and Aphyosemion louessense is known from localities in the Kouilou system upstream of the Sounda Gorge (van der Zee 2014, pers.comm.).There is a complete separation of coastal plain and inland Aphyosemion species due to the Du Chaillu Massif geography and variation in climate, and it is unlikely that these species were sampled in the lower Kouilou catchment (van der Zee 2014, pers.comm.).

Figure 1 .
Figure 1.Location of study sites in the Kouilou, Noumbi and independent coastal basins, Lower Guinea ichthyofaunal province, Republic of the Congo.

Figure 2 .
Figure 2. Examples of major habitat types sampled: A) Forest stream; B) Coastal savannah stream; C) Kouilou River; D) Swamp forest; E) Savannah wetland; F) Lake Ngonzo; G) Estuary opening to the Atlantic Ocean; H) Mangrove.

Figure 3 .
Figure 3. Fishing techniques applied in the survey: A) Cast nets; B) Fyke nets; C) Gill nets; D) Seine nets; E) Electrofishing; F) Scoop nets; G) Hook and line; H) Observation of local fishermen's catch showing Heterotis niloticus and Parachanna sp.

Table 2 .
List of species collected in the study region shown per habitat type.FS = Forest Streams, CSS = Coastal Savannah Stream, R = River, SF = Swamp Forest, SW = Savannah Wetland, L = Lake, E = Estuary and M = Mangrove.

Table 3 .
Species collected in the study area shown per basin and compared to previous data collected in the area .K = Kouilou basin; N = Noumbi basin; CB = Independent Coastal basins.