Morphometric and Allozymic Characterisation and Genetic Variation in Three Species of Chrysichthys in Ghana

Abstract

Chrysichthys species have been characterised by previous investigators. Most often, characterisation has been based on morphological and meristic characters. These characters may be modified by environmental factors, thus making them difficult to use in characterising species. There is the need therefore to refine or supplement taxonomy based on morphological and meristic characteristics. In the present study, variation in meristic counts and twelve body proportion variables in three species of the Catfish, Chrysichthys from two river basins (Volta and Densu) in Ghana were evaluated for their reliability in separating the species. Position of the longest dorsal soft fin ray and the number of branched pectoral fin rays were found to be stable and dependable in the identification of the three species. Body proportion values showed wide ranges which overlap so much that they do not give precise identification of species. In addition to the moiphometric study, variation at 15 loci involving eleven proteins were studied by allozyme electrophoresis in each of the species to (i) identify loci that discriminate between species, (ii) estimate levels of genetic variation among C. auratus, C. nigrodigitatus and C. maurus, (iii) estimate phonetic relationships among populations and species, and (iv) indicate whether there are any significant differences in the genotypic frequencies of populations. Seven discriminating loci were found between C. auratus and either C. nigrodigitatus or C. maurus. At the loci investigated, genetic variation was generally low in all the species. It was highest in C. auratus and least in C. nigrodigitatus [Polymorphism, P, (l% criterion) = 0.178 in C. auratus, 0.133 in C. maurus and 0.089 in C. nigrodigitatus-, Heterozygosity, He, = 0.029 in C. auratus, 0.016 in C. maurus and 0.009 in C. nigrodigitatus]. There were no significant genetic differences between populations within C. auratus and C. nigrodigitatus (average gene diversity between populations, Dst, = 0.001 in both species). Again based on lod screened, the closest species genetically were C. nigrodigitatus and C. maurus (Genetic identity, I, = 0.999) while the most distant species were C. auratus and C. maurus (I = 0.525). There were no significant changes in the genotypic frequencies of the populations (X205 ranges from 0.020 to 2.292 for polymorphic loci).