Molecular Evolution and Genetic Analysis of Silver Catfish (Chrysichthys nigrodigitatus) in Nigeria

Background and Objective: In a disrupted environment such as the Niger Delta, studies of population genetic diversity and molecular evolution can provide useful information necessary for species conservation and population management. This study was therefore designed to evaluate selection types, demographic expansion, mutation types as well as the maternal lineage of C. nigrodigitatus. Materials and Methods: Fifty mature Silver catfish were collected from fresh and brackish waters for this study. Muscle tissue was excised from each fish and preserved in 95% ethanol for DNA extraction and analysis. Extraction and purification of mtDNA from fish muscle tissues were carried out using the Quick-gDNA^TM MiniPrep kit (Zymo Research, USA). The sequenced fragments were viewed and edited using ChromasPro software and subsequently analyzed using suitable software. Results: Tajima’s D value was 2.091 (p<0.05) in freshwater fish samples and 1.292 (p>0.10) in brackish water fish samples, while Fu’s Fs value for fresh and brackish water fish samples was 1.667 (p<0.02) and 1.108 (p>0.10), respectively. Maternal lineage analysis revealed that C. nigrodigitatus used in this study may be traced to Clarias gariepinusand Clarias macrocephalus based on the hypervariable region of the mitochondrial DNA. Positive, negative and neutral selection pressures were detected in both populations, while mutation analysis revealed synonymous and non-synonymous, transversion and transition, deletion and insertion mutations in both populations. Conclusion: The findings of this study suggest that there is high genetic polymorphism in the populations of Silver catfish evaluated as well as the molecular similarity between freshwater and brackish water samples. It was also revealed that the origin of Silver catfish is traceable to Clarias gariepinusand Clarias macrocephalus.