Comparative Morphology Of The Sagittal Otolith In Four Sebastes Spp. From The Bohai Sea And The Yellow Sea

The otolith organs of the inner ear of teleost fishes are mechanoreceptors thatprocess acoustic and postural information. They are comprised of three calcareousstructures in the inner ear of teleosts: lapillus, asteriscus and sagitta. Generally, thesagittae are the most widely used in comparative taxonomy because of their large size,degree of interspecific variation and relative ease by which the structures can beaccessed. Nowadays, the otolith shape analysis has proven to be a powerful time-andcost-efficient means in species identification, stock separation and taxonomy ofmarine fish species. Moreover, otolith morphology analysis also can be applied inecomorphological studies. It has been suggested that the species-specific otolithmorphology is determined by synergistic influences of both genetic andenvironmental components. The environmental factors and life style of each species isvaried. As mechanoreceptors that process acoustic and postural information, otolithsbear a close relationship to the ambient stimuli. Sebastes is the most speciosescorpaenid genus with approximately110species known worldwide, among whichthe majority are distributed in temperate to Arctic waters throughout the North Pacific.Seventy species are distributed within the northeast Pacific (NEP), and33speciesoccur in the northwest Pacific (NWP).Two approaches have been mainly used forspecies identification and taxonomic analysis of Sebastes: traditional phenotype-basedspecies identification and biochemical and genetic approaches. With the developmentof relevant techniques and analysis methods sagittal otoliths has be applied in speciesidentification and taxonomy of genus Sebastes. However, the applications of otolithshape analysis to species separation in Sebastes spp. from the northwest Pacific arevery rare.The species considered in this paper were four sympatric species of the genusSebastes that belong to four subgenera inhabiting rocky reefs in shallow coastal waters: Sebastes schlegeli (Hilgendorf,1880), S. hubbsi (Matsubara,1937), S. nudus(Matsubara,1943) and S. thompsoni (Jordan et Hubbs,1925). They are four typespecies from different subgenus. All the four species are known to be closely related,as expressed by the small magnitude of meristic and morphometric differences andclose phylogenetic relationships. This study was to discriminate four Sebastes speciesin the coastal waters of the Bohai Sea and the Yellow Sea by means of otolith shapevariables (a combination of shape indices and elliptic Fourier coefficients) analysis.Accordingly, the primary aims of this paper were to (i) describe the characteristics ofsagittal otoliths of the four species systematically,(ii) analyze otolith shape variabilityand examine its potential in species separation and (iii) investigate the possibleinfluence of genetic and ecological and environmental variables on otolithmorphological features. The main findings are as follows:(1) CDA of standard length-corrected otolith shape variables (a combination ofshape indices and elliptic Fourier coefficients) provided a higher overall speciesclassification success rate within the four NWP Sebastes species than that within theNEP species (94%) and the North Atlantic (NA) samples (88%);(2) The otolith morphological affinities coincide well with the phylogeneticrelationships reported among these species, which indicates the potential to use otolithmorphology to establish phylogenetic relationships in this genus;(3) The ecomorphological comparisons suggest that the otolith shapes might beinfluenced by several ecological and environmental components such as depth, bodycolor and substrate type. Among the environmental factors, depth could be the mostcomprehensive factor associated with the inter-specific variations of otolithmorphology;(4) By comparing the mean otolith shapes of Sebastes from NWP, NEP and Atlantic,we speculated that within genera, environmental effects on modification of otolithshape may be more significant for the allopatric species with long-term geographicisolations whereas genetic effects may be more obvious among sympatric species.