The developmental process of all osteological elements except the scale in the red sea bream, Pagrus major, was described from prelarvae to late juveniles.The larvae at first-feeding stage exhibited only some elements of head skeleton and pectoral fin-supports, which were mostly cartilaginous structures except the maxillary and cleithrum.The completion of osteological structures was characterized by the formation of accessory cartilages 7 and 8 of the caudal skeleton and the ossification of middle radials of dorsal and anal fin-supports.Reared and wild specimens reaching this stage seemed to be different in size.An attempt to summarize the osteological development was made on the basis of the counts of considerable changes, e.g., the initial appearance of cartilage, the full complement of cartilages, the beginning of ossification and the full complement of ossified structures for respective elements.A histogram of those counts against total length consisted of several peaks suggesting the ontogenetic intervals in this species.
The dentition of the ayu, Plecoglossus altivelis, changes during young stages (Matsui, 1938;Chapman, 1941;Suehiro, 1942;Iwai, 1962;Komada, 1980a).In this paper, the development of teeth on the upper jaw are described to be compared with the developmental pattern of teeth on the lower jaw.The present study was based upon about 100 specimens from Lake Biwa (Kohokucho, Shiga Pref.) and about 180 hatchery-reared specimens, measuring from 24 to 60mm in standard length (SL).In the histological examination of jaws, some specimens were serially sectioned at a standard thickness of 8μm.The sections were mostly stained with hematoxiryn-eosin and some stained with azan.The other specimens were stained with alizarin red S. The first indication of the formation of comb-like teeth is observable at 70 day old specimen (about 24mm SL).At about 32mm SL, 100 day old, a thin stratum of dentine appeared between the ectodermal columnar cells and odontoblast.Then the number of tooth groups on the upper jaw was about seven and about three on the lower jaw.Each tooth group consists of 10 to 20 separated denticles.The teeth constituting the tooth group is roughly in rod shape on the lower jaw and small canine like teeth on the upper jaw.On the upper jaw, teeth located at the anterior part of each tooth group are ankylosed with the pre-maxillary and maxillary, and, they erupt at this stage.The primordia of comb-like teeth are laid externally and separated from the dentary on the lower jaw.At about 40mm SL, teeth on the upper jaw are rod-shaped and they are separated from the pre-maxillary and maxillary.At this stage, the form and arrangement of teeth consisting the comb-like teeth on the upper jaw are similar to that on the lower jaw.These results suggest that the comb-like teeth on the upper jaw are usable to catch micro-crustaceans at the juvenile stage.
The spawning period and migration of the rose bitterling, Rhodeus ocellatus (Kner) in a small pond, Shimizu-ike, Osaka Prefecture, were investigated from November 1973 to December 1975. It was suggested that the population was composed mainly of 0-to 3-year-old fish, and the sex ratio was comfirmed to be one.The spawning period was assumed to be from March to September.Means of both ovipositor length and the proportion of individuals possessing ripe eggs of 2-and 3-year-old females took the highest value from April to the end of May, and that of 1-year-old fish was the highest in late July.The minimum size for reproduction was 23-24mm in body length. In spawning season, males migrated toward the shore where bivalves were distributed in a high density, and matured females migrated several times between the offshore and the near shore, i.e., after they laid eggs into bivalves at the shore they returned to the offshore.