ARI Volume 2 Number 1.pdf - Zoo-unn.org

EYO, Joseph Effiong 28210Figure 7: Karyotype of Clarias albopunctatus from Anambra river, Nigeria8Short Arm (S) %Relative chromosome length in percentage642012345678910112 32 34 5 645 67 87 89910 1110 1112 13 14 15 1617 18 19 2012 13 14 15 16 17 18 19 20Long Arm (L)%212122 23 2422 23 24Figure 8: An idiogram of the karyotype of male Clarias albopunctatus showing themorphology of the chromosomes. The 0 represents the position of the centromereTeugels et al. (1992) reported 2n = 52 forHeterobranchus longifilis Valenciennes, 1840 and2n = 54 in the hybrid of C. gariepinus vs. H.longifillis.The result of the present studiesindicated that the karyotypes consisted more ofsubmedian chromosomes in C. ebriensis and C.anguillaris and almost equal number of submedianand terminal chromosomes in C. gariepinus and C.albopunctatus in which the centromeres wereclearly defined. Differences in chromosome sizeswere observed, but were very gradual and at nopoint were the variations greater than errorinvolved in the method of measurement. Similarkaryotypes were described for C. gariepinus(Ozouf-Costaz et al., 1990) and H. longifilis(Teugels et al., 1992) strains used for aquaculture.The observed chromosomal divergence betweenthese clariids species was consistent with theirmorphological differences (Eyo, 2003). The almostuniformity of chromosome number andmorphology within the clariids may also suggestsuccess with which many species will hybridize.Crosses between clariids (C. gariepinus vs Hlongi ilis) f using artificial fertilization method havebeen reported (Teugels et al., 1992). In nature,the occurrence of chromosome number aroundmodal values among the clariids may suggest thatchromosomal changes may be associated with theprocess of speciation within the group, possiblythrough high rate of hybridization resulting fromcommunal spawning. Information on thechromosome number among siluriform fishesindicated that diploid chromosome number forcatfishes range from the mid-20’s to well over 100with most species having a diploid set in the mid-40’s to upper 100’s, but no clear modal numberhave been suggested. An increase in diploidchromosome number is associated with aconcomitant change in arm number. In the studyof chromosome number among the siluriformfishes, Fitzsimons et al. (1988) noted that a diploidchromosome number of 56 ± 2 was widespread