High genetic diversity and population differentiation in Clarias gariepinus of Yala Swamp: evidence from mitochondrial DNA sequences

Mitochondrial DNA Corroborates the Genetic Variability of Clarias Catfishes (Siluriformes, Clariidae) from Cameroon

The airbreathing walking catfish (Clariidae: Clarias) comprises 32 species that are endemic to African freshwater systems. The species-level identification of this group is challenging due to their complex taxonomy and polymorphism. Prior to this study, the biological and ecological studies were restricted to a single species, Clarias gariepinus, resulting in a biased view of their genetic diversity in African waters. Here, we generated the 63-mitochondrial Cytochrome c oxidase subunit 1 (COI) gene sequences of Clarias camerunensis and Clarias gariepinus from the Nyong River in Cameroon. Both C. camerunensis and C. gariepinus species maintained adequate intra-species (2.7% and 2.31%) and inter-species (6.9% to 16.8% and 11.4% to 15.1%) genetic distances with other Clarias congeners distributed in African and Asian/Southeast Asian drainages. The mtCOI sequences revealed 13 and 20 unique haplotypes of C. camerunensis and C. gariepinus, respectively. The TCS networks revealed distinct haplotypes of C. camerunensis and shared haplotypes of C. gariepinus in African waters. The multiple species delimitation approaches (ABGD and PTP) revealed a total of 20 and 22 molecular operational taxonomic units (MOTUs), respectively. Among the two Clarias species examined, we found more than one MOTU in C. camerunensis, which is consistent with population structure and tree topology results. The phylogeny generated through Bayesian Inference analysis clearly separated C. camerunensis and C. gariepinus from other Clarias species with high posterior probability supports. The present study elucidates the occurrence of possible cryptic diversity and allopatric speciation of C. camerunensis in African drainages. Further, the present study confirms the reduced genetic diversity of C. gariepinus across its native and introduced range, which might have been induced by unscientific aquaculture practices. The study recommends a similar approach to the same and related species from different river basins to illuminate the true diversity of Clarias species in Africa and other countries.

DNA barcoding to characterize biodiversity of freshwater fishes of Egypt

The current study represents the first molecular characterization of freshwater fish species in Egypt from two major fish resources; the River Nile and Lake Nasser. A total of 160 DNA barcodes using a 655-bp-long fragment of the mitochondrial cytochrome oxidase subunit I (COI) gene were generated from 37 species belonging to 32 genera that represent 15 families from nine orders. The studied species were identified using different molecular-based identification approaches, in addition to the morphological identification, including neighbor-joining (NJ) trees, Barcode Index Number, and Automatic Barcode Gap Discovery (ABGD). The average genetic divergence based on the Kimura two-parameter model (K2P) within orders, families, genera, and species were 0.175, 0.067, 0.02, and 0.008, respectively. The minimum and maximum K2P distance-based genetic divergences were 0.0 and 0.154, respectively. Nucleotide diversity (π) varied among families and ranged between 0.0% for families Malapteruridae, Auchenoglanididae, Schilbeidae, Anguillidae, Centropomidae and Tetraodontidae and 17% for family Cyprinidae. The current study cautions against the lack of species coverage at public databases which limits the accurate identification of newly surveyed species and recommends that multiple methods are encouraged for accurate species identification. The findings of the current study also support that COI barcode enabled effective fish species identification in River Nile and Lake Nasser. Moreover, the results of the current study will establish a comprehensive DNA barcode library for freshwater fishes along the River Nile in Egypt. Egyptian freshwater fish DNA barcodes will contribute substantially to future efforts in monitoring, conservation, and management of fisheries in Egypt.

DNA and eDNA-based tracking of the North African sharptooth catfish Clarias gariepinus

The African sharptooth catfish, Clarias gariepinus, contributes much to the River Nile ecosystem by its high omnivorosity, sturdiness, growth rates, and fecundity. It was globally appreciated as a key fluvial aquaculture species. Yet, it is also one of the top world freshwater aliens. Monitoring the genetic diversity of different economically and ecologically important species as well as development of markers that aid their tracing and abundance are fundamental. This is chiefly due to the growing international threats of environmental pollution, reduction, and loss of biodiversity. Herein, the genetic diversity of C. gariepinus along the River Nile in Egypt was assessed through sequencing of the mitochondrial cytochrome oxidase subunit I (COI). Also, a qPCR assay based on C. gariepinus 16srDNA was developed to assess the species abundance through environmental water DNA samples (eDNA). The results showed low genetic diversity of that species in Egypt. Moreover, its populations exhibited high rates of fixation. Testing its eDNA-based marker resulted in an unambiguous quantitative trend in situ, in agreement with reports of local fishermen. These eDNA signals were strong at least 1 Km upstream to the initial sampling areas, even where no C. gariepinus fishing activities are carried out. This possibly indicated a degree of homogenous species-abundance in each of the studied areas. Finally, the results identified a need for better conservation strategies for C. gariepinus, since its low diversity in the Egyptian River Nile may represent a threat against its persistence under the continuously changing environmental conditions. Moreover, using non-invasive sampling methods, e.g. based on aquatic eDNA quantification, can aid much the detection of areas of abundance of C. gariepinus, especially for both the economic importance it contributes and the invasive power it possesses.