Study Of Taxology, Morphology And Genetics Of Brownspot Flathead

Flathead fishes of the genus Platycephalus, order Scorpaeniformes, familyPlatycephalidae, are widely distributed in the tropical and temperate areas of theIndo-West Pacific. They are demersal species with commercial value. By now,16species of the genus have been formally documented, of which two are reported to bedistributed in the region of Northwest Pacific. They are Bartail flathead(Platycephalus indicus) and Platycephalus cultellatus. In addition, two other validspecies of the genus Platycephalus in the waters of Northeast Asia have long beenrecognized and classified, one of which is Platycephalus sp.1(Japanese nameYoshinogochi) and the other is Platycephalus sp.2(Japanese name Magochi). Severalstudies on biology, taxology and genetics of the two species have been done byJapanese ichthyologists. In China, P. indicus has long been recognized as the onlyspecies in the genus Platycephalus in Chinese coastal waters. However, based onwide scale sampling data, it is found that Platycephalus sp.1is not only inhabitChinese coastal waters but also the most widely distributed one of the genus. Basedon its morphological characters, Brownspot flathead is proposed to be its trivial name.Aiming at providing references for taxonomic and systematic study of the genusPlatycephalus, and offering basic information for resource protection, studies in thisthesis were implemented.1. A new record of Brownspot flathead in China and redescription of Bartail flathead174specimens of the genus Platycephalus were collected from the coastal watersof Dongying, Qingdao, Zhoushan, and Beihai. Samples were identified as Brownspotflathead morphologically. The coloration, meristic traits, and morphometricmeasurements were consistent with previously published records. In brief, it is anorange-brown flathead fish with dark brown spots scattered on head and body, lateral line scales83to99with one or two spine-bearing anteriormost pored scale, no yellowblotch on the caudal fin. Cytochrome oxidase I subunit (COI) gene fragments weresequenced for phylogenetic analysis. The mean evolutionary distance within thespecies Brownspot flathead was0.1%. Net evolutionary distances between Brownspotflathead and other species of the genus Platycephalus ranged from10.8%to19.7%,which is much greater than the threshold for species delimitation. The COI sequenceanalysis strongly supports the validity of Brownspot flathead at genetic level.Redescription of Bartail flathead and comparison with Brownspot flathead wasalso provided here. The diagnose characters of P. indicus are: lateral line scales73~80,scales above the lateral line15~16, gill rakers6~8(2~3+4~6); caudal fin with2~3black bars, a yellow blotch in middle of the fin.2. Morphological diversity of sagittae of Brownspot flatheadThe sagittae morphology of Brownspot flathead from the coastal water ofQingdao was studied. The results showed that the sagittaes of Brownspot flatheadcould be classified into five types basing on their morphology differences lie onExcisural Notch, Radiate Stripes, Ventral Posterior Crystals and Dorsal Crystal. Theone-way ANOVA test based on77coefficients derived from the elliptical Fourieranalysis demonstrated that the percentage of significantly different coefficients couldbe up to13%in pairwise comparisons of the five sagittae types. The reconstructedcontours by the Fourier analysis perfectly revealed the morphological features ofdifferent sagittae types. The following statistic result showed that the percentage ofevery sagittae types not only changed as the sagittae length and somatic lengthchanging but also changed between left and right sagittaes and different sex. Due tothe diversity of the sagittae morphology of Brownspot flathead, it is essential to takeall the five sagittae types into consideration when doing researches on sagittaes ofBrownspot flathead. The effect of the left and right and the sex on the frequency ofdifferent types of sagittaes should also be taken into account.3. Morphological variation analysis of demes of Brownspot flathead166specimens of Brownspot flatheads were collected from the coastal waters ofDongying, Qingdao, Zhoushan, Changle and Beihai.21standardized morphological characters were chosen for the statistical analysis of morphological variation. In theprincipal component analysis, scatter of component factor score was made based ontwo principal components with the highest contribution ratio. The scatter pooleddemes of Zhoushan, Changle and Beihai into one group, while demes of Dongyingand Qingdao into another. The one-way ANOVA showed that the number ofsignificantly different morphological characters of pairwise comparison among thefive demes ranged from7to15. In the discriminant analysis, Fisher’s discriminantfunctions were established by stepwise method. Discriminant accuracy was87.5%to100%, which is a relatively high value. It is presumed that prey and environmentalquality may play a role in the forming of morphological differentiation by affectingthe growth rate of Brownspot flatheads of different demes. Besides, the nonuniformsampling date may also have an influence on the statistical analysis.4. Population genetics of Brownspot flathead168specimens were collected from9demes of Brownspot flathead in Chinesecoastal waters. Sampling period was during2010.7to2013.1. Basing on510bp’sfragment in mtDNA control region, genetic diversity, population structure anddemographic history were analyzed. The total number of haplotype was43, in whichthe main haplotype accounted for55%in frequency. Haplotype diversity for eachdeme ranged from0.53to0.95, while nucleotide diversity varied between0.002and0.007. The pairwise φstwere at low level (-0.031~0.051). The result of AMOVAshowed that all the molecular variation could be explained mainly by variance withindemes. No significant population genetic structure was detected. MST was in theshape of a star, which demonstrated a recently demographic expansion. The mismatchdistribution and BSP analysis both indicated that the expansion event occurred morethan10,000years ago. Compared with other species of the Northwest pacific whichalso experienced expansion, this demographic event came relatively later. It ispresumed that the process of reconstruction of benthic ecosystem after the LastGlacial Maximum may be the main reason for the delay.