The order Tetraodontiformes is one of the most derived fish group and comprises approximately 350 species of fishes displaying an incredible range of morphological diversity. The group consists primarily of tropical and subtropical marine reefdwellers. It could be further divided into 2 suborders, 6 superfamilies, 10 families and 100 genera. We have used mitochondrial gene sequences as molecular markers to reconstruct the phylogeny of Tetraodontiformes, Tetraodontidae and Takifugu Abe. Molecular phylogenetic trees were constructed using the maximum parsimony, neighbor-joining, maximum likelihood, and Bayesian methods. We have estimated the divergence time of Tetraodontiformes and Tetraodontidae based on their phylogeny. During the time, we have identified a new species of Takifugu Abe. The main conclusions and hypotheses of the present study were as follows.
1. Two individuals in genus Takifugu Abe were collected from the estuary area of Peal River in Humen Town, Guangdong Province, China. These two specimens were identified as a new species, named Takifugu lini. It distinguished from all other species of Takifugu with: small and thin prickles on their back and abdomen; doral and vental spinose areas separated; small pectoral blotchs with slanting pitching; an unconspicuous fuscous band on back connecting zygomorphic pectoral blotch; alive green-brown grounding on back; many nacarat vermiculate speckles distribute from snout area to the back of tail-petiole. The species could only be found in the briny-fresh water area in estuary of Peal River.
2. Pufferfishes of genus Takifugu Abe (Tetraodontiformes, Tetraodontidae) are comprised of a comparatively small number of species and are mainly distributed along the coastal region of the western part of the Sea of Japan and the coastline of China. Mitochondrial gene sequences were employed to test the phylogenetic hypotheses within the genus. Seventeen species of the genus were examined. Our hypothesis of internal relationships within the genus differs from previous hypothesis. Our results indicated that (1) genus Takifugu is a monophyletic assemblage; (2) the genus is divided into six subgroups based on the molecular data; and (3) there is low genetic diversity among the species within the genus. In addition, speciation within Takifugu appears to be driven by hybridization and isolation by distribution. Our results also suggested that the taxonomy in the genus should be clarified based on both molecular and morphological data.
3. Tetraodontidae is a main group in order Tetraodontiformes, which primarily of tropical and subtropical pelagic, benthic slope-dwellers, and brackish and freshwater species. Twenty-eight species of the family were examined. Different methods were used to reconstruct the molecular phylogenetic trees. Then we estimated the divergence time of the main groups in Tetraodontidae. Our results indicated that (1) Tetraodontidae is a monophyletic group and could be divided into two clades; (2) the genetic distance of different groups is close in molecular level, which implied the divergence time was close or the speed of differentiation was fast; (3) with respect to the divergence times obtained, the origin of the Tetraodontidae is estimated here is about 32.84～34.81Myr.
4. The order Tetraodontiformes consist of 10 families. All of these families are included in this analysis. Different methods were used to reconstruct the molecular phylogenetic trees. We estimated the divergence time of the main groups in Tetraodontiformes. Our hypothesis of internal relationships within the genus differs from previous hypothesis. Our results indicated that (1) Tetraodontiformes is a monophyletic group; (2) we brought forward a more clearly phylogeny of the group in molecular level; (3) with respect to the divergence times obtained, the origin of the Tetraodontiformes estimated here is about 97.99～103.42Myr.