| The Rokel River(also Seli River;previously Pamoronkoh River)is the longest and the largest in Sierra Leone.It is estimated to be 10,622 km~2,with the drainage separated by the Gbengbe Kabala hills and the Sula Mountains.The Rokel River rises in the 900 meters(3,000 foot)high interior plateau of the Loma Mountains in the Guinea Highlands of north-central Sierra Leone,drifts southwest about 240 knots(390 km~2)through hill ranges and,together with a smaller,corresponding stream called Port Loko Creek,runs into the Rokel estuary before flowing into the Atlantic Ocean.One particular characteristic of the river is the Bumbuna Falls,a cascade of around30 m in height,just above the site of the Bumbuna Hydroelectric dam.This area is one of the most overlooked ichthyofaunal basins,despite the potential for concealing diversity and a high level of endemism.Thirteen sites/locations were selected for this study,including the river basin’s upper,middle,and lower reaches.A total of 2000 specimens were collected during our visit to the RR basin.We compared the taxonomic checklist across studies conducted by private research groups in the ecoregion.Which accounted for 97 native and two introduced species,60 genera,and 25 families recorded.The family Cichlidae is by far the most prominent,representing 23(24.71%)of the total species diversity,followed by Cyprinidae 16(16.49%),Mormyridae 13(13.40%),Mochokidae 7(7.20%),and Alestidae 4(4.12%).In contrast,the remaining are represented by three species or less.The DNA molecular phylogeny of freshwater fishes from this river is rare.Morphological features alone are inadequate for precise species identification.Here,a phylogenetic analysis based on the COI,Cytb genes,and two species delimitation methods detected at least 18 fish species displayed high intraspecific distance,with each of these species formed a distinct clusters.This study also observed a disjunct distribution in some genera from the RR basin.Their sister genera suggest that this river had a past complex interbasin connection exchange with the nearby river basins of Zaire and lower Guinean ecoregions.The unrecognized diversity observed from some taxa or genera of this area may have significant implications for biodiversity conservation.This study also revealed the presence of several misidentifications within the Auchenoglanis occidentalis,Brienomyrus brachyistius,Isichthys henryi,Mormyrus tapirus,Hippopotamyrus paugyi,Enteromius,and Labeo groups.The analysis concluded that the genus Mastacembelus aff.Liberiensis here delineated represent undescribed species.This species is morphologically similar to the M.liberiensis complex but mainly differs in diverse aspects.These findings lead to the following conclusions:(1)hidden species diversity of spiny eels exists in either the Rokel River or the Jong River basin;(2)a likely available name for this species from the Freetown Peninsula is M.laticauda distinct from M.liberiensis;(3)given the diversity within M.liberiensis observed in the rivers sampled in Sierra Leone,it seems likely that the remaining rivers of Liberia and Sierra Leone reported having M.liberiensis may also harbor undescribed diversity.Furthermore,the study observed an allopatric distribution between species reported for this study and those of the Little Scarcies/Forécariah river basin.And also an intriguing biogeographic pattern was observed among paired species Labeo aff.coubie of the RR basin(upper Guinean)and Labeo coubie from the Niger basin(Nilo-Sudan)ecoregions.So far,the Futa Djallon highlands intercept these two ecoregions,but little is known about the ancient connections of many of these smaller coastal rivers or streams.This disjunct distribution cannot be explained by river capture.Likely,forest formation theory,widely used to define the biogeographic pattern found in vertebrates,can be utilized as a reasonable elaboration for their disjunct distribution.More research on inter-and intra-specific relationships between different taxa occurring in neighboring rivers or ecoregions could help unravel the complex biogeographic patterns of this area.In addition,this study described three new species Enteromius kassiensis,Enteromius gberiensis and Enteromius rokelensis,from the Rokel River basin.These new species are found within the upper portion of the river basin.These populations are distinguished from all congeners by possessing a greater head distance(27.8-37.5 % SL),head width(69.7-72.0 % SL),13-15 lateral line scales between the third black spot to the second;27 lateral line scales;5 lateral scales between the first black spot to dorsal-fin origin,and a brown-goldish,silveryish on the belly.The resulting phylogenetic analysis based on the Cytb gene of all these new species are more closely related to populations within lineages that comprises typically species distributed in the Nilo-Sudan,East Africa(Lake Victoria)and west-central Africa(Lower Guinea)Provinces.We assert that all previously described species of Enteromius ablabes,E.liberiensis and E.foutensis are not present in the Rokel River basin.Several aspects distinguish the potentially new species from all congeneric species of West Africa(Upper and Lower Guinean Provinces).This study highlighted a need to put the current morphology-based species of this area under molecular scrutiny,as indicated in previous investigations.Therefore,it is essential to expand the application of an integrative(i.e.,traditional taxonomy and DNA molecular)approaches and the incorporation of several freshwater systems of the country as these will likely contribute to the identification of currently unknown diversity and offer insights into the patterns of endemism of freshwater fishes of this area and the broader Upper Guinea ecoregion. |
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