Otolith morphology of teleost fishes of Japan

In order to examine the diversity and generality of otolith morphology, we observed and measured saggital otoliths of 550 species from 162 families of Japanese fishes. In chapter 1, we reviewed the research history on otolith morphology and presented the terminology used in this paper. In chapters 2 through 8, morphological characteristics such as external form, side form, sulcus form, annual structure in the otolith surface and its section, and metrical characteristics （otolith length, width, and area index, length:height ratio, and relative size） were described for each species. We examined otolith characters that could be used to identify fish species and taxa based on these characteristics. In the last chapter, the diversity and generality of external otolith form and size and their evolutionary, systematic, ecological and functional morphologies were discussed. For the external shape, the ellipsoidal otolith is a general morph. Elongate types, with a otolith length:height ratio over 3.0, occurred in 16 species of Coryphaenoides pectoralis， Anoplopoma fimbria, Scorpaenopsis cirrosa, Scopelosaurus hoedti, Synodontidae fishes, Platycephalidae fishes, Sphyraena japonica, Lepidocybium flavobrunneum, Ruvettus pretiosus, and tuna species. A rectangular type was found only in 3 species （Scomber fishes and Katsuwonus pelamis） and a tall elliptical type was found in 8 species, suggesting that these types can be used as diagnostic characters. Indeterminate otoliths, shaped like a sailboat, were a unique shape occurring in Zeidae and Tetraodontidae species. Approximately 75 % of all species have outside warped otoliths. Inside warped （backwarped） otoliths occurred in some fish species, i.e. Monocentris japonica, Slangichthys microdon, Pleuronichthys sp., and Cynoglossus robustus. Sulci in the otoliths of over 75 % of species were formed from the excisura major to the core or the posterior otolith margin. Rounded sulci were found in some Pleuronectiformes and Gobiidae species as well as several species such as Ilyophis brunneus, Pisodonophis zohistius, Acromycter nezumi, Paraliparis sp., and Malthopsis annlifera. Putting these otolith characteristics together, over 40 ％ of species have warped ellipsoidal otoliths with a sulcus formed from the excisura major to around the posterior margin, which was recognized as a typical pattern. Oppositely excluded otolith morphs were available for diagnostic characteristics. In this study, only 70 species （about 12 % in all fishes） could be identified based on the combination of external otolith characters. But many genera or families have otoliths with distinguishable traits, and our descriptions would therefore be useful for identifying fish taxa by observing the otolith morphology. The evolutionary phylogenetic nature of otolith morphology was unclear through the description in this study, because almost all types of external shapes, side forms, and sulci occurred across taxa. If we focus on the relationship with life style （habitat）, demarsal fish species have both orbicular and elongate otoliths, and we conclude that life style does not determine the otolith external shape. But over 80 % species with well-developed sulci in otoliths belonged to the Clupeidae, Salmoniformes, Gadiformes, Hexagrammidae, Acropomatidae, Serrannidae, Apogonidae, Carangidae, Haemulidae, Sparidae, Gempylidae, Scombridae, and Tetraodontiformes, all of which are characterized as migratory pelagic species or schooling rocky fishes. On the other hand, over 60 % of species with poorly developed sulci belonged to the Angulliformes, Platycephalidae, Scorpaenidae, Cottidae, Liparidae, Zoarcidae, Stichaeidae, Gobiidae, and Pleuronectiformes, which are characterized as settled demarsal species. Beside them, the otolith sulci in the genus Sebastes were shorter in the shallower habitats. The functional morphology of the otolith sulci seems to be important in understanding the relationship between otolith morphology and life style. In general, larger body length correlated with smaller relative otolith size within and between-species. Fishes with a relative otolith size （otolith length ×1000/total body length） under five were spindle-shaped fishes, eel-like fishes, Istiophoridae species, and Tetraodonti-formes species. Conversely, fishes with large-sized otoliths have allometrically large heads. Therefore, relative otoith size was determined by the relative head size and/or the body shape of the taxon, rather than life style, habitat, migratory habit, or evolutional phylogeny. Otolith length:height ratios could be also understood in relation to the head shape, as with the otolith size.