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

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.