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

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Cytogenetic variations in Clarias species 283Figure 9: Karyotype of Clarias gariepinus from Anambra river, Nigeria109Relative chromosome length in percentage876543210012345678911226 73 4 56 78 98 9Short Arm (S) %12 13 141015 1923 24 25 161117 18 20 21 2226 27 2823 24 2512 13 14 19151016 26 27 2820 21 2217 1811Long Arm (L)%10Figure 10: An idiogram of the karyotype of male Clarias gariepinus showing themorphology of the chromosomes. The 0 represents the position of the centromereamong 70 species of catfishes in 10 families andwas especially frequent in four families, theAriidae, Bagridae, Ictaluridae and Pimelodidae.The observed range for the clariids 2n = 48 to 2n= 56 fall below the speculated 2n = 56 ± 2 rangeof Fitzsimons et al. (1988). Thus the range for theclariids may be put at 2n = 52 ± 4. The observedsimilarities in chromosome number although withalmost similar morphometric and meristiccharacters may explain the placement of both C.anguillaris and C. gariepinus in the subgenusClarias (Clarias) by Teugels (1982). The disparityin chromosome number (Eyo, 1997) along withdissimilar morphometric (Eyo, 2002; 2003) andmeristic (Eyo, 2004b) characters of C. ebriensisand C. albopunctatus from C. gariepinus and C.anguillaris may equally explain the placement of C.ebriensis and C. albopunctatus in the subgeneraClarias (Anguilloclarias) and Clarias (Clarioides)respectively.Karyological evidences have beenemployed in solving problems relating tochromosome number, functional arm, phyleticrelationship, the taxonomic status as well aspossibility of speciation among the studied Clariasspecies. For instance the wide dispersal ofchromosome number around modal value (2n =56) among the clariids suggested possibilities ofthe species undergoing speciation.Conclusively, the grouping of Clariaseither as macroclarias or as megaclarias based onsimilarities in size and morphological featureshould be adopted as a stock management tool.The key diagnostic characters (Eyo, 2003) as wellas the relationship between standard length andmorphometric characters (Eyo and Inyang, 2003)may be adopted by clariid taxonomist.
EYO, Joseph Effiong 284Relative chromosome length in percentage10987654321001234567891011Figure 11: Karyotype of Clarias anguillaris from Anambra river, NigeriaShort Arm (S) %2 3 5 610 114121315 16 17 18 1924 25 267 8 91420 21 22 2327 2824 25 265 610 11 12 13 15 16 17 18 192 3 427 2820 21 22 23147 8 9Long Arm (L)%Figure 12: An idiogram of the karyotype of male Clarias anguillaris showing themorphology of the chromosomes. The 0 represents the position of the centromereThe cytotaxonomy of the clariids places them intotwo chromosomal number types; 2n = 56represented by C. anguillaris and C. gariepinus,and 2n < 56 as in C . ebriensis and C.albopunctatus justifies the managerial designationof the clariids into megaclarias and macroclarias.ACKNOWLEDGEMENTThe author acknowledges Drs. N. M. Inyang andB. O. Mgbenka for supervising the PhD thesis fromwhich this paper was extracted. Furthermore,greatly acknowledged are, the Nigerian Academyof Science for their Postgraduate fellowship awardin 1993; and Prof. G. G. Teugels (late), Drs. D. H.J. Sydenham and H. M. G. Ezenwaji for identifyingthe species and provision of relevant researchdocuments. Finally, I am thankful to Nkiruka Ezefor typesetting the manuscript.REFERENCESBLAXHALL, P. C. (1981). A comparison of methodsused for the separation of fishlymphocytes. Journal of Fish Biology, 18:177 – 181.EYO, J. E. (1997). Morphometric and cytogeneticvariations among Clarias species(Clariidae) in Anambra rive r, Nigeria. PhDThesis, Department of <strong>Zoo</strong>logy, Universityof Nigeria, Nsukka. 267 pp.EYO, J. E. (2002). Conspecific discrimination inratio morphometric characters amongmembers of the Pisces Genus: Clarias
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