Identification,Classification And Molecular Phylogeny Of Sciaenidae Species From Chinese Waters

The family Sciaenidae,commonly known as croakers and drums,is a large taxonomic group in the order Perciformes,comprising about 270 species in 70 genera in the world.The sciaenids are commonly found in shallow coastal waters of tropical to temperate seas,estuaries and rivers,occurring abundantly over sandy or muddy bottom.A few species are found in other regions like coral reefs,deep sea or freshwater.Because of lacking strong sw,imming ability,most Sciaenidae species distribute regionally.The sciaenids usually are commericially important,and some species are important in capture and aquaculture fisheries in China.Chinese researches on sciaenids can date back to the 1930s and reached its prosperous time in the 1960s.To date the identification and inter-generic relationships of this taxonomic group remain controversial because of the limitation of traditional taxonomy and the lack of comprehensive review.No croakers’ fossil sample was found in Asia,the West-Pacific region,thus the origins,evolution and dispersal patterns of the Sciaenidae also remain controversial.The present study collected sciaenids’ specimen along coastal waters of China during 2014-2017 covering the Yellow Sea,the East China Sea,the Taiwan Strait and the South China Sea;identified Sciaenidae species,described and compared the morphological characters among different species;obtained the mitochondrial genomes of the sciaenids;analysed phylogenic relationships of Sciaenidae species and estimated the divergence time of the Sciaenidae.The main results were addressed as below:(1)Based on the combination of sampling from fishing ports,wet markets and bottom trawling surveys,totally 26 sciaenid species were identified and arranged into 13 genera based on morphological characters.In addition to the valid species Bahaba taipingensis which was not collected by this study,there are 27 Sciaenidae species belonging to 14 genera in coastal waters of China.New keys to the genera of Sciaenidae and to the species of every genus were composed.Among 27 sciaenid species,the genus Johnius has the highest diversity with 8 species,including J.grypotus and J.trewavasae which were identified in the 1990s,and one new species in the genus of Johnius(Johnius sp.).(2)External morphology,mental pores,gill raker,swim-bladder and otoliths of 26 sciaenids were documented through photo capture.Based on characteristics of mental pores,sciaenid species were divided into 5 forms(Six pored-form,Five pored-form、Flase five pored-form、Four pored-form and Two pored-form);Based on characteristics of swim-bladder,sciaenid species were divided into 10 forms(Sciaenops-form,Argyrosomus-form、Bahaba-form,Larimichthys-form,Atrobucca-form,Otolithes-form,Megalonibea-form,Pennahia-form,Nibea-form and Johnius-form);Based on characteristics of otoliths,sciaenid species were divided into 7 forms(Johnius-form,Dendrophysa-form,Argyrosomus-form,Atrobucca-form,Pennahia-form,Miichthys-form and Larimichthys-form).(3)Complete mitochondrial genomes of 11 sciaenids were analysed in this study.Mitogenomes of species of non-Johnius genera followed the typical vertebrate canonical organizations,having a length from 16408～16842bp,comprising 13 protein coding genes,2 rRNA genes and 2 main nocoding regions.ND6 and 8 tRNA genes(tRNA-Gln,-Ala,-Asn,-Cys,-Tyr,-Ser(UCN),-Glu and-Pro)are coded in the L chain,other genes are coded in the H chain.A nucleotide bias against G was found in species of non-Johnius genera.Mitogenomes of species of the genus Johnius have a length from 18073-19468bp,the phenomenon of gene rearrangement occurred in the sequence between tRNA-Thr to tRNA-Leu(UAA)(containing tRNA-Pro,Dloop,tRNA-Phe,12S rRNA,tRNA-Val and 16S rRNA).A nucleotide bias against A was found in species of the genus Johnius.(4)Monophyly of the family Sciaenidae and monophyly of the genera Collichthys,Larimichthys,Johnius and Nibea are well supported by the phylogenetic tree.Three main branches are detected.Argyrosomus japonicus and Sciaenops occelatus formed the first branch which was placed distantly to other sciaenids in Indo-West Pacific,indicating that Argyrosomus japonicus may have different origin.Bahaba taipingensis,Miichthys miiuy,the genera Collichthys and Larimichthys clustered in the second branch.The third branch was formed by 19 species.In the third branch,Atrobucca nibe and Otolithes ruber were placed outside other 17 species.Megalonibea diacantha,Chrysochir aureus and the genus Pennahia formed a sub-branch,the genus Nibea,Dendrophysa russelii and the genus Johnius formed another sub-branch.(5)The origin of the family Sciaenidae was estimated at 27.41～24.21 million year ago(MYA)(Late Oligocene)in this study.The divergence time between the first branch and other branches was estimated to be 24.21 MYA(Late Oligocene)while the divergence time between the second and the third branch was estimated to be 18.96 MYA(Early Miocene).It is indicated that divergence of sciaenids in Indo-West Pacific was occurred after the divergence of Atlantic species,and the hypothesis which considers New World as the origin of the Sciaenidae is supported by this study.Existing croakers in coastal waters of China was estimated to be diverged at Middle Miocene.Divergence time in the genus Pennahia and the genus Johnius was estimated to be earlier than in the genus Nibea,the genus Collichthys and the genus Larimichthys.The latest divergence occurried between Johnius grypotus,Johnius trewavasae and a new recorded species,Johnius sp.,which may occurred at 1.66 MYA(Pleistocene).