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Both fish and humans have evolved from an ancestral bony vertebrate 450 million years ago.The teleost fish comprises more than 24,000 species and accounts for more than half of all extant vertebrate species,representing the most successful and diverse group of vertebrates.It displays remarkable variation in morphological and physiological adaptations.Entire genome duplications in the teleost fish are important mechanisms for enabling morphological and functional innovation in evolution.Diverse genomes of teleost fish provide insight into species evolution.To better use zebrafish genome as a model in biological studies,we have comparatively analyzed genomes among the sequenced fish genomes including zebrafish.The chromosome numbers in zebrafish are at the first peak representing third whole-genome duplication event(WGD)in ray-finned fish lineages.A WGD event can be identified by large segmental duplications(SDs)in the genome.We performed whole-genome assembly comparisons to identify large SDs in zebrafish and other species.Compared to other fish,zebrafish(9.1%)genome showed the great number of SDs.Other teleost fish species harbored the less SDs,including medaka(5.3%),pufferfish(5.3-8.1%),threespine stickleback(7.8%).Interestingly swamp eels showed the least numbers of SDs(1.6%),similar to the 1.7% in the human genome.Thus,zebrafish appeared to have maintained a considerable portion of the genome after the third WGD in comparison with other fishes,suggesting a complexity of zebrafish genome.