Discrimination and habitat
characteristics of larvae and juveniles
|
Masahiro Kobayashi*, Hirofumi
Shimizu**, Kei-ichi Mito*, Masaya Katoh* and Takeo
Kurihara* |
| ABSTRACT |
| Habitat characteristics of larvae and juveniles of coastal fishes were estimated according to the differences of species and their sizes for samples collected by various methods. But it is necessary to discriminate larvae and juveniles of fish species using the biochemical discrimination methods, because they cannot be discriminated morphologically. |
| INTRODUCTION |
| Coastal fishes in the subtropical area including Yaeyama Islands include many commercially important species. But in recent years, the resources of important fishes have shown a tendency to decrease and are in a serious condition. It is necessary to manage the resources of fishes for maintenance and continuous fisheries. For this purpose, it is necessary to investigate the whole life cycle of each species. However information on eggs, larvae and juveniles of fishes living in this sea area is limited, therefore it is not possible to classify the eggs, larvae and juveniles of important coastal fishes. The purpose of this study is to try to discriminate larvae and juveniles morphologically and to estimate their respective habitats. |
| RESULTS |
| Larvae and juveniles which live in the coastal
waters of the Yaeyama Islands were collected
by juvenile collecting net which was towed
on the surface of the sea horizontally and
in the sea diagonally, by a fish-luring light,
and by a surf zone net. As a result of collection
using the above methods, it was presumed
that the larvae and juveniles of different
species were collected by the different methods,
that is to say, different places (Table 1).
Therefore, it is assumed that larvae of Lethrinidae
move from the middle-deep area of offshore
to the coastal surface as their grow. But there were very few morphological differences on which to differentiate the species of the larvae and juveniles, and it was not possible to classify them into genus and species. For example, larvae of the genus Lethrinus are characterized by a thin serrate bulge on the back of the head (Fig. 1, a), and a serrate, elongate spine at preopercular angle (Fig. 1, b), but the characteristics have not been confirmed for all species of Lethrinus yet. And it is not possible that the larvae can be discriminated to the species level exactly, because morphological characteristics of each species have still not been confirmed. Larvae of Lutjanidae (Fig. 2, a~c) and of Caesionidae (Fig. 2, d) are in a similar situation. Therefore, it is necessary for strict discrimination of species to discriminate them using biochemical methods such as DNA and allozyme techniques. |
| Fig 1 Larva of
genus Lethrinus. a. Side view, b. Dorsal view (the same individual) It has a thin serrate bulge on the back of the head (a), and a serrate, elongate spine at preopercular angle (b). |
| Fig 2 Larvae of Lutjanidae (a~c) and Caesionidae
(d).
a~ c : They are shown with the pelvic soft ray elongated which characterizes in Lutjanidae, but thought to be are different species based on body forms and pigmentations. d : Larva of Caesionidae is remarkably similar to the larvae of Lutjanidae, and can be discriminated from larvae of Lutjanidae by a difference in the numbers of anal and pelvic fin rays. But it can not be discriminated to the species level. |
| Table 1 Comparison of the frequencies of larvae and juveniles of coastal fishes collected by the different methods. |
