Tema: Digestion De Enzimas De Restriccion Del Adn Lambda

Nature and Science, 6(1), 2008, naturesciencej@gmail.com, ISSN: 1545-0740 Karyotypic diversity of some tilapia species Sofy H.I. 1, Layla A.M. 2, Iman M.K.A. 2
1 2

Head of Veterinary Division, National Research Centre, Egypt. Department of Hydrobiology, National Research Centre, Egypt. imankam_2@yahoo.com

Abstract: This study present cytogenetic analyses of three fish species in Egypt,Oreochromis niloticus, sarotherodon galilaeus and Tilapia zillii belonging to cichlids, with a mean objective of contributing for a better understanding of the relationships between these species and the probability of their hybridization. The karyotypes of these species have been investigated by examining metaphase chromosomes spreads obtained from headkidney cells. The diploid chromosome numbers ofall three species were 2n=44. The karyotypes of Oreochromis niloticus were one pair of submetacentric; 13 pairs of subtelocentric and 8 telocentric ; Sarotherodon galilaeus showed one pair of metacentric, 6 pairs of submetacentric; 7 pairs of subtelocentric and 8 pairs of telocentric chromosomes . The chromosomes of Tilapia zillii were,10 pairs of submetacentric ;5 pairs of subtelocentric and 7pairs of telocentric chromosomes . There was a significant difference between the mean lengths of the haploid sets of chromosomes of fishes under investigation. The cytogenetic characteristics partaken by the species analyzed in the present study reinforce and the probability of hybridization between Oreochromis niloticus and sarotherodon galilaeus ,but less chance between Tilapia zillii andOreochromis niloticus or , sarotherodon galilaeus. [Nature and Science. 2008;6(1):19-27]. ISSN: 1545-0740. Keywords: karyotypic diversity, tilapia, chromosomes. Introduction The importance of fish taxonomy is not only with description of new forms, but also with placing each form within taxonomic system that shows it’s relationships to other forms .For more than a century, systematists have sought toorganize this diversity by studying aspects of their external and internal morphology which have been especially successful in defining species and in organizing these species into genera. These groupings have usually been confirmed when examined with cytogenetically approaches. Tilapia is a generic term used to designate a group of commercially important food fish belonging to the family Cichlidae;Cichlids are classified in the large order Perciformes, which consists of three aquacultural important genera- Oreochromis niloticus, sarotherodon and Tilapia, they inhabit the fresh and brackish waters . Tilapia have been receiving increased scientific study as they have important species in tropical aquaculture. The classification of the Tilapiines relies heavily on the differences in breedingand brooding behavior to discriminate between species at the generic or subgeneric level. Karyological studies of fishes can contribute significantly to the solution of many problems in areas of research ranging from taxonomy, systematic or genetics to phylogenetics, or environmental toxicology (Alsabti ,1985) . In the last few decades works have been focused on the field of cytogeneticinvestigation of fishes, especially in the area of systematics, mutagenesis and aquaculture. The karyotype is the chromosome complement of an individual or related group of individuals, as defined by chromosome size, morphology and number. Though for all somatic cells of all individuals of species, the number of chromosomes is used as an indicator of classification of species of chromosomes andinterrelationships within families. The studies of these characters help to investigate the aquatic structure for the investigate the aquatic structure for the population of each species population in each habitat, so it can determine what

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Nature and Science, 6(1), 2008, naturesciencej@gmail.com, ISSN: 1545-0740 species are related to each other in an accurate manner?. This may help to facilitate...