トウゴロウイワシの初期生活史

抄録

In Nagasaki Prefecture during 1981, larvae and juveniles of Allanetta bleekeri were collected from June to October with a larva net and dip net in Omura Bay, and immature individuals were collected under fish lamps in Nomo Harbor from April to December.Morphological development, local occurrence and food composition, especially in larval and juvenile stages, were studied.
A.bleekeri reaches the juvenile stage at sizes of 13.2-15.6mm in total length.The common morphological characteristics of other species of the Atherinidae were observed in larvae and juveniles.These include round head, short trunk, long and compressed tail, melanophore procession along the dorsal edge of the body, longitudinal black stripe formed laterally, fin fold remaining till early juvenile stage.The following points are important to distinguish larvae and juveniles of A.bleekeri from those of the other species of the same family, due to their supposedly sympatric occurrence: presence of melanophores on rear of notochord and caudal fin base, presence of ventral melanophore procession between pelvic and anal fins, and reach of lateral stripe.Relative growth during the early developmental stages is divided into three phases: larval, juvenile (up to 20-25mm in total length), and ault-form stage.
Larvae were collected with a larva net from the surface layer.They occurred abundantly from June to early September along the coast where Zostera marina or Sargassum spp.grew thick.Their occurrence is thought to have started in May.Larva net collection showed rather extensive distribution in the young larval stage.Well-grown larvae and juveniles were observed to form concentrated schools along the sea-wall of a harbor in September and October.
Investigation on food composition in digestive tracts revealed A.bleekeri to be a zoo-plankton feeder mainly relying on Copepoda and its larvae.