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

Animal Research International (2005) 2(1): 275 – 286 275CYTOGENETIC VARIATIONS IN Clarias species (CLARIIDAE:SURULIFROMIS) OF THE ANAMBRA RIVER USINGLEUCOCYTES CULTURE TECHNIQUESEYO, Joseph EffiongDepartment of Zoology, University of Nigeria, Nsukka, NigeriaABSTRACTCytogenetic variations among four Clarias species from Anambra river, Nigeria were studiedusing leucocytes culture techniques. Heterogeneity in chromosome number (2n = 48 inClarias ebriensis and C. albopunctatus to 2n = 56 in C. anguillaris and C. gariepinus) andKaryotype morphologies occurred among the cl ariids . The chromosomes were characterizedby a high proportion of meta-submetacentric chromosomes and low proportion of acrocentricchromosomes . The females karyotype morphologies exhibited a heteromorphic pairsuspected to be the sex chromosome complex. The following formulae were established forthe male clariids; C . ebriensis 6m + 22sm + 20a FN =76; C.albopunctatus 4m ± 22sm + 22aFN = 74; C. gariepinus 8m + 24a FN = 88; and C. anguillaris 8m + 26m + 22a FN = 90. Thef emale karyotype morphologies were C . ebriensis 6m + 23sm + 19a FN = 77, C. albopunctatus4m ± 23sm + 21a FN = 75, C. gariepinus 8m + 25sm + 23a FN = 89 and C. anguillaris 8m +27sm + 21a FN = 91. A generic chromosomal number of 2n = 54 + 4 for the clariids wassuggested. The almost uniform karyotype morphologies and the closeness of the chromosomenumbers around the generic chromosome number may suggest success with which theclariids may hybridize in nature.Keywords: Cytogenetics, Chromosomes, Karyotype, Idiogram, Clarias, Clariidae, Leucocyte cultureINTRODUCTIONKaryological evidences have often been utilized insolving problems relating to speciation, identity ofsex determining chromosome, phyleticrelationship, the taxonomic status and identity ofboth interspecific and even intergeneric hybridsamong organisms. Concerning speciation, newevidence suggests that karyotype plays a primaryrole (White, 1978) contrary to Mayr (1963) originalhypothesis that only polyploidy and geographicalisolation lead to the formation of new species.Fish comprises polyphyletic group which hasundergone an enormous expansion, the number ofexisting species totals about 20,000 (Lagler et al.,1977). This is about 48.10 % of all the existingvertebrates. The capacity of this group to adapthas led to their colonization of extremelyspecialized niches. Pisces explosive expansioncannot be explained wholly in terms ofgeographical isolation since chromosomemechanism probably plays a role in speciation(Sola et al., 1981).About 1000 to 1500 species have beenstudied out to the 20,000 species (Lagler et al.,1977). Evidence has been found of evolution bypolyploidization in the Cypriniidae (Wolf et al.,1969) and Salmoniidae (Ohno et al., 1969) usingkaryological techniques. In salmonids currentlyundergoing expansion, chromosome polymorphismswere shown (Thorgaard, 1977). In thePoecilids, speciation may occur by interspecifichybridization. This apparently applies to Poeciliaformosa Bloch, 1801; whose hybrid origin is widelyaccepted based on morphological and karyologicalcharacteristics (Prehn and Rasch, 1969).The teleosts provide good materials forcytologists working on sex determinationproblems. In most species sex chromosome areabsent or not morphologically identified. However,some species are known to exhibit maleheterogamete whereas others have femaleheterogamete. Kallman (1973), reported thatallopathic populations of the same species maydisplay female or male heterogamete as shown inXiphophorus maculates Hecke, 1848 in which thesex chromosomes were identified by means ofpigment gene marker showing a sex-linkedhereditary patterns. Feldber et al., (1987) showedthe occurrence of chromosome system for sexdetermination of ZZ/ZW type in Semaprochilodustaeniurus Newton, 1978 (Pisces: Prochilodontidae)which is lacking in Semaprochilodus insignis C. andV., 1929. Chromosome W found in the femalewas the largest in the complement. ChromosomeZ was the next largest complement and tentativelyconsidered as pair number one in males. Heaf andSchmid (1984) have shown sex-chromosomedifferentiation in another poecillid species, Poecilliasphnops var. melonistica Jordan and Snyder, 1906.