Molecular Systematics Of The Genus Hysterothylacium(Ascaridoidea: Anisakidae) From Marine Fishes Of China

Hysterothylacium Ward&Magath,1917is one of the largest g roups of the familyAnisakidae in the order Ascaridida. Adults of Hysterothylacium commonly occur in thedigestive tract of marine, estuarine and freshwater fishes and their larvae parasitize varioustissues of numerous fishes and invertebrates, which can affect the health of the fish hostsand even cause their death, with consequent economic repercussions.In th e present study, morphological features combined with molecular techniques,utilising the internal transcribed spacer (ITS) of nuclear ribosomal DNA (rDNA) as agenetic marker, have been successfully used for accurate identification of Hysterothylaciumnematodes collected from the marine fishes off the coast of China at the species level foradults and larvae. The main results as follows:1) Three new species of Hysterothylacium were described: H. longilabrum Li, Liu&Zhang,2012collected from the Mottled spinefoot Siganus fuscescens (Houttuyn) andWhite-spotted spinefoot S. canaliculatus (Park)(Perciformes: Siganidae) in the SouthChina Sea; H. zhoushanensis Li, Liu&Zhang,2012collected from the Roughscaleflounder Pseudorhombus oligodon (Bleeker)(Pleuronectiformes: Paralichthyidae) in theEast China Se a; H. simile Li, Zhang&, Liu,2012collected from the Japanese seabassLateolabrax japonicus (Cuvier,1828)(Perciformes: Lateolabracidae) in the Bohai Sea.Molecular analyses by sequencing and comparing the internal transcribed spacer (ITS) ofthe riboso mal DNA of the three species, respectively, with the closely related nematodesequences seem to support the validity of th e new species based on the morphologicalobservation.2) Hysterothylacium thalassini Bruce,1990collected from the Purple-spotted bigeyePriacanthus tayenus Richardson and Red bigeye P. macracanthus Cuvier (Perciformes:Priacanthidae) and H. tetrapteri (Bruce&Cannon,1989) collected from the Striped marlinKajikia audax (Philippi,1887)(Perciformes: Istiophoridae) in the South China S ea wereredescribed and both species are reported in Chinese waters for the first time. The ITSregions of H. thalassini and H. tetrapteri w ere compared with Hysterothylacium spp. inGenBank, and the results seem to support the validity of the incompletely known species.3) Specimens originally identified as Contracaecum paralichthydis Yamaguti,1941[now H. paralichthydis (Yamaguti,1941)] by Xü (1957), collected from the Yellow stripedflounder Pseudopleuronectes herzensteini (Jordan&Snyder)(Pleuronectiformes: Pleuronectidae) in the Yellow Sea, were also re-examined. The ir morphology clearlyrevealed they belong to H. aduncum (Rudolphi,1802), which is also redescribed based onXü's material. In addition, the morphological variation of caudal papillae i n H. aduncumfrom P. herzensteini was compared, using scanning electron microscopy, with specimenscollected from another three fish hosts, Lophius litulon (Jordan)(Lophiiformes: Lophiidae),Scomberomorus niphonius (Cuvier)(Perciformes: Scombridae) and Cleisthenesherzensteini (Schmidt)(Pleuronectiformes: Pleuronectidae), from the Yellow Sea.4) The third and fourth stages larvae of H. longilabrum and H. zhoushanensis wereexactly identifi ed and described by analyzing and compar ing t he ITS sequence with theadults for the first time.Furthermore, A catalog of all the Hysterothylacium nematodes including70recognizable species was provided based on the published information.