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 phenetic

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

x i i

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).