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

EYO, Joseph Effiong 276Karyotype evolution and geographicaldistribution among fishes have been studied. Inthe genus, Oryzias; Oyzidae, Uwa (1986), Uwaand Parenti (1988) and Uwa et al., (1988) dividedthe rice fish into three groups: monoarmedchromosome type (O. melastigma Jordan andStarks, 1906 (Uwa and Iwata, 1981) O. javanicusJordan and Starks, 1906 (Uwa and Iwata, 1981),biarmed chromosome type O. sp. (Oryzias species)(Uwa and Magtoon, 1986) O. curvinotus Jordanand Starks, 1906 (Uwa, et al., 1982), and fusedchromosome type (O. celebensis Jordan and Seale,1906 and O. minutillus Jordan Starks, 1906 inSouth and South Eat Asia to the Indian ocean.The biarmed chromosome types are distributed inEast Asia and Luzon. The degree of the karyotypeevolution by increased of biarmed chromosomenumber in this group seems to correlate with thegeographical distribution from Indo-China to Japanand Luzon to China. Members of the fused armchromosome types are found in Sulawesi andThailand.Cytogenetical investigations amongteleosts has revealed inter and intra-specificvariations in nucleolar organizing region (NOR).Feldberg and Bertollo (1985) noted among the neotropical cichlids that the NORs were located on thefirst chromosome pair in the complement andcoincided with secondary constrictions observedthere, whereas in Cichlasoma facetum Swainson,1839 and Geophagus brasilcensis Heckel, 1840,the NOR were located on another chromosomepair. NORs have been investigated in several fishspecies, such as Carassius sp. Nilsson, 1832(Funaki et al., 1975; Ojima and Yamano, 1980),Umbra limi Gronow, 1763 (Kligerman and Bloom,1977), cichlid fishes (Kornfield et al., 1979),Fundulus diaphanous Lacepode, 1803 (Howel andBlack, 1979). In the fish species, the NORs wereusually located near the telomeric regions ofsatellite chromosomes except for F. diaphanouswhere they were located on the secondaryconstriction of the sex chromosomes. The NORsare of obvious importance to geneticists.Kligerman and Bloom (1977) reported that theNORs are sites of prior genetic activities and wheresatellite chromosomes occur. This chromosomepair could serve as an adequate marker as inUmbra limi.The interests of cytogeneticists andevolutionists are closely connected with that ofichthyologists in the study of hybrids. In thefreshwater bony fish, evidences were frequentlyfound in interspecific and even intergeneric hybridswhere sympatric populations of different speciesexist. The development of fish culture hasresulted in numerous experiments on hybridizationto obtain new strains, which are more diseaseresistant, faster growing than their relative wildstock. In such case, karyological knowledgeallows the parent species to be recognized andgive some indication of the likelihood of success inthe case of artificial crossbreeding. Furthermore,it may help to make predictions concerning hybridfertility and the interactions of two parental stocks.Although it is not possible to drawabsolute conclusion about phyletic relationshipsfrom karyological comparison of different species,karyotype analyses have supplemented othertaxonomic evaluating methods. The systematicdefinition of species depends on a carefulmorphological analysis, and the karyotype is amajor morphological character among severalothers.The phyletic relationship among thesiluriform fishes based on karyotype and variationin chromosomal number revealed that, Bagremarinus Catesby, 1771 had 2n = 54 chromosomescomposed of 12 metacentric, 8 submetacentricand the remainder with terminal or near terminalcentromere (Fitzsimons et al., 1988).Furthermore, the karyotype of three species ofariid catfishes (Arius dussumier C and V, 1840,Arius felis C and V 1840 and Bagre marinus)indicated the same diploid chromosomal number,but each species had a different arm number.Data for 132 species in 14 families of catfishesindicated a predominance of 56 ± 2 chromosomesin the diploid set (Fitzsimons et al., 1988).According to them, the range in diploid numberwas most common among the Ariidae, Bagridae,Ictaluridae and Pimelodidae, which together havebeen suggested from osteological evidence asforming a group close to the ancestral stock fromwhich present day catfish evolved. In a study ofchromosomal evolution among the Ictaluridcatfishes, LeGrande (1981) observed that a diploidchromosome number of 56 ± 2 was wide among70 species of catfishes in 10 families and wasespecially more frequent in four families, theAriidae, Bagridae, Ictaluridae and Pimelodidae. Inaddition, average diploid count of 56 modal countfor catfishes were approximated from the averagesand / or modal counts of ariids, (all 54), bagrids(mostly between 50 and 60, with a weak mode at52), clariids (50, 52 and 56), ictalurids (mostlybetween 56 and 60 with exclusion of divergentkaryotype in Noturus) and Primelodids (mostly 56).LeGrande (1981) hypothesized an ancestralkaryotype of 2n = 56 for Ictalurids and pointed outthat the closeness in this number to thosereported for the Ariidae, Bagridae and Pimelodidaecoincides with Gosline (1975 a, b) suggestion thatthese families plus Doradidae constitute a groupnear the ancestral stock from which living catfishesevolved. Considering the Clariids, Teugels et al.(1992) reported a standard karyotype of 2n = 56for Clarias gariepinus and 2n = 52 forHeterobranchus longifilis Valenciennes, 1840.Their hybrids revealed an intermediate karyotype