Abstract
BackgroundThe tilapia family of the Cichlidae includes many fish species, which live in freshwater and saltwater environments. Several species, such as O. niloticus, O. aureus, and O. mossambicus, are excellent for aquaculture because these fish are easily reproduced and readily adapt to diverse environments. Historically, tilapia species, including O. mossambicus, S. melanotheron, and O. aureus, were introduced to Hawaii many decades ago, and the state of Hawaii uses the import permit policy to prevent O. niloticus from coming into the islands. However, hybrids produced from O. niloticus may already be present in the freshwater and marine environments of the islands. The purpose of this study was to identify tilapia species that exist in Hawaii using mitochondrial DNA analysis.Methodology/Principal FindingsIn this study, we analyzed 382 samples collected from 13 farm (captive) and wild tilapia populations in Oahu and the Hawaii Islands. Comparison of intraspecies variation between the mitochondrial DNA control region (mtDNA CR) and cytochrome c oxidase I (COI) gene from five populations indicated that mtDNA CR had higher nucleotide diversity than COI. A phylogenetic tree of all sampled tilapia was generated using mtDNA CR sequences. The neighbor-joining tree analysis identified seven distinctive tilapia species: O. aureus, O. mossambicus, O. niloticus, S. melanotheron, O. urolepies, T. redalli, and a hybrid of O. massambicus and O. niloticus. Of all the populations examined, 10 populations consisting of O. aureus, O. mossambicus, O. urolepis, and O. niloticus from the farmed sites were relatively pure, whereas three wild populations showed some degree of introgression and hybridization.Conclusions/SignificanceThis DNA-based tilapia species identification is the first report that confirmed tilapia species identities in the wild and captive populations in Hawaii. The DNA sequence comparisons of mtDNA CR appear to be a valid method for tilapia species identification. The suspected tilapia hybrids that consist of O. niloticus are present in captive and wild populations in Hawaii.
Highlights
With easy breeding and high survival rates, the tilapia family of the Cichlidae has been an excellent species for aquaculture
The phylogenetic tree generated from mtDNA CR sequences successfully differentiated population H (O. niloticus) from population E and B, both of which are species of O. aureus (Figs 1 and 2) while the phylogenetic tree based on mtDNA c oxidase I (COI) data failed to differentiate the species O. aureus and O. niloticus
Except the clustering of the species O. niloticus and O. aureus, all other tilapia species clusterings based on the COI sequence data are consistent with the results from the mtDNA CR sequence data
Summary
With easy breeding and high survival rates, the tilapia family of the Cichlidae has been an excellent species for aquaculture. In these countries, tilapia aquaculture provides dietary sources of protein and minerals for millions of impoverished families but is an important means for economic and social empowerment. Mosambique tilapia (O. mossambicus) and its hybrids can tolerate high salinity and are increasingly used in coculture with marine shrimp [3,4]. The tilapia family of the Cichlidae includes many fish species, which live in freshwater and saltwater environments. Several species, such as O. niloticus, O. aureus, and O. mossambicus, are excellent for aquaculture because these fish are reproduced and readily adapt to diverse environments. The purpose of this study was to identify tilapia species that exist in Hawaii using mitochondrial DNA analysis
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