Development of median and paired fin skeleton of Paralichthys olivaceus (Pleuronectiformes: Paralichthyidae).

Development of median and paired fins and their supports are described for Paralichthys olivaceus,giving details on origin,shape,ossification and meristic counts.All fin supports begin to form through cartilage in the following sequence:pectoral(2.62mm SL),dorsal(4.60mm SL), caudal(5.55mm SL),anal(5.95mm SL) and pelvic fin support(8.57mm SL).Completion and partial ossification of fin structures are already present by the 40th day after hatching(ca.16mm SL),after eye migration.This study shows how developmental osteology may clarify identification and terminology of fish bones(e.g.,caudal skeleton).Comparisons with other species belonging to Pleuronectiformes elucidate basic pattern of fin formation within the order,and depict interesting departures which may be of taxonomic and/or systematic utility. Paralichthys olivaceus is one of the most exploited flounder in Japanese waters probably because its abundance close to shore.Actually this species is also the subject of extensive artificial propagation.Despite the increase in fundamental knowledge about this flounder (e.g.,Okiyama,1967;Tsuruta and Omori,1976; Minami,1982;Kuwahara and Suzuki,1982), information on osseous structure is scarce and incomplete(Amaoka,1969),and as far as could be determined only Okiyama's studies(1967; 1974) contribute to knowledge on osteological development.Studies on the osteological development provides various information about functional aspects of larval survival as well as providing a potential tool for taxonomic and systematic works(Dunn,1983). This paper deals with the development of median and paired fins and their support of Paralichthys olivaceus giving details on their origin,shape,ossification and meristic counts. Materials and methods A total of 164 specimens of Paralichthys olivaceus was used in this study.Of them,154 were laboratory-reared and ranged from 2.62 to 17.43mm in standard length(SL) 0-42 days after hatching(a.h.).Specimens were reared at the Japan Sea Farming Association,Miyako Station(Iwate Prefecture),and Kyoto University,Maizuru Fisheries Research Station(Kyoto Prefecture).Fourteen wild-caught specimens ranging from 38.90 to 107.15mm SL(locality unknown),were kindly supplied by Dr.T. Minami.Reared specimens were preserved in either 5 % buffered formalin or Bouins solution, whilst wild specimens were fixed in 10 % formalin. Clearing and staining were done by Dingerkus and Uhler's(1977) method.However,specimens fixed in Bouins were greately decalycified, and were therefore used only for cartilage observations.Since formalin even at as low a concentration as 5 % decalcifies bone,it may be presumed ossification took place a little before that stated in this work. Observations and drawings were made with a Wild M5 and Nikon SMZ10 stereoscopic microscope with the aid of camera lucida.Measurements of smaller specimens were made with a Nikon V20 profile projector associated to a Nikon SMZ6F digital counter,and by a calibrated ocular micrometer attached to a microscope.Larger specimens were measured with a Kanol dial caliper.Fin rays and pterygiophores were counted regardless of their degree of development;counts on paired fins included both sides.