When this fish grows to about 13.5mm. in total length, the first scute appears on the shoulder region of lateral line. Scute formation of this fish begins a little earlier than that of Gasterosteus aculeatus aculeatus, Pungitius pungitius and P. sinensis (IGARASHI, 1962, '63, '64). This first appeared scute is, in fact, situated the fifth numbered from anterior most one when the scute formation is completed. Starting from this fifth scute, the order of appearance is 5th-6th-4th-3rd-2nd-lst.
This fish having six scutes of anterior series only, the formation of posterior series, which is degenerate, differs from that of Gasterosteus aculeatus aculeatus. The scute forma-tion stops when the fish reaches about 20 mm. in total length, completed in scute arrangement of Gymnura type. In this size the fish matures. In this respect the author supposes it shows an instance of “neoteny” in comparison with those of Gasterosteus aculeatus aculeatus. Fundamentally the scute developmental process of this fish resembles that of Gasterosteus aculeatus aculeatus. It shows this fish has phylogenetical similarity to that fish, though it differs markedly from him in fish size in scute appearance, order of scute appearance, ar-rangement of scute as well as in degeneration of posterior series scute formation, etc.. And as a whole, structure of the scute of this fish showing more or less tendency of degeneration. From these facts the author supposes that this fish should be an independent species in Genus Gasterosteus, not a subspecies of Gasterosteus aculeatus aculeatus.

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