In Egypt, four species of Tilapia have been described based on
morphometric, meristic and cytotaxonomical characteristics. These
species are Tilapia zillii, Oreochromis niloticus, Oreochromis aureus
and Sarotherodon galilaeus. The accurate identification of these
fishes is complicated by the high variation in these characters,
similarity among species and in some cases by the size of the fish. In
this paper, we examined the use of polymerase chain reaction (PCR)
and restriction fragment length polymorphisms (RFLPs) analysis of
the nuclear small subunit ribosomal RNA gene (srDNA) for
molecular identification of Tilapia spp. in Egypt. The present study
aims to evaluate such advanced molecular biological approach for
identification of Tilapia spp. Genomic DNA was extracted from the
four species of Tilapia. About 2000 bp 18S ribosomal DNA was
amplified by PCR using specific primers. The technique of restriction
fragment length polymorphisms was used to identify the specific 18S
rDNA for each species. O. niloticus rDNA 'RFLPs species-specific
pattern is proved by digestion with restriction endonucleases AIwNI
and Aval, On the other hand, digestion of amplified 18S rDNA with
endonuclease enzymes Smal, Xmal and Sstll produced speciesspecific
patterns for T. zillii, O. aureus and S. galilaeus respectively.
This indicates the efficiencies of these restriction endonuclease
enzymes in species-specific identification of Tilapia spp. Restriction
fragment length polymorphisms of the nuclear srDNA (RFLPsPCR)
proved to be a good tool for checking the relationships among species
and their subspecies, even more than the morphological analysis.