The African mud catfish ( Clarias gariepinus ) is well known for its nutritional and economic importance and it’s the most important cultured fish species in Nigeria. Its sustainable production is being threatened by inbreeding depression occasioned by the use and reuse of imported frys and fingerlings from exotic homogenous stocks. Knowledge of genetic variation of this important fish species is needed to improve its efficiency of breeding and for possible identification . Morphological, genetic, and molecular studies were carried out to determine the residual genetic variability and assess the possibility of improving the fish quality through selective breeding of local strains.
Growth performance was examined by heterosis performance on Specific growth rate ( SGR), Hatchability, survival, and mean growth over a period of 26 weeks through reciprocal crossings of different strains, while the molecular analysis examined the selection traits through protein profiling using Sodium deodosulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, and genetic differentiation using random amplified polymorphic DNA (RAPD) assay and microsatellite analysis. Morphological comparisons revealed morphometric homogeneity between C. gariepinus fish population in River Benue and River Niger and their tributaries which clustered into five considerably distinct populations.
The growth performance analysis shows significant difference in mean weight gain, specific growth rates and survival rate (P<0.05). Sokoto sourced strains (SKT) gave the best growth of 595.00±4.33g, closely followed by its reciprocal hybrid with South African strains (SA ♀ X SKT ♂) 554.00±6.22g, while the New Bussa strain had the lowest growth value (70.00±2.07g) at the grow-out level . The cross between the Dutch and Yola strains gave the highest positive mean heterosis of 28.54% (P<0.05).
The DNA- RAPD analysis recorded an overall low polymorphism among and within the local and exotic populations of C. gariepinus in Nigerian freshwater bodies and their reciprocals (19.35%). However, considerably higher levels of polymorphism were detected between the Lokoja Ganija strains (29.67%) and Yola strains (12.09%). The nine microsatellite loci used to screen the wild C . gariepinus strains and their crosses germplasm revealed polymorphic information content (PIC) values that ranged from 0.077±0.231 to 0.395±0.399 with the local strains showing slightly higher allelic diversity than the three exotic strains. This study demonstrated that the seven local strains population of Nigerian C. gariepinus species screened contained higher allelic and gene diversity as compared to the cultured exotic populations. It therefore identified and recommends the Sokoto and Yola strains (for growth performance) and Lokoja, Sokoto and New Bussa strains (for genetic variability) as possible founder stocks and viable substitute to the much-touted exotic strains for the catfish aquaculture industry in Nigeria.
Key Words: Clarias gariepinus, Cross breeding, Strains , Microsatellites, Genetic variation