イトヨGasteroteus aculeatus aculeatus LINNAEUS (陸封型)の稜鱗の発達について

抄録

The formation of the scutes in three-spined sticleback, Gasterosteus aculeatus aculeatus LINNAEUS does not arise until the fish grows to 15mm in total length. When the fish reachs to the length about 15mm, four primary scale-like particle shaped scutes appear on the shoulder region. From there the scute formation runs toward the anterior and posterior directions and finally they complete the anterior series of scutes. Apart from these anterior scutes, new posterior scutes appear on the posterior region of the side of caudal peduncle when the fish grows to the length of about 20mm, the scute formation running from there mainly in the posterior direction, and after a while they complete the posterior series of scutes. At last when the fish grows to about 40mm, both anterior and posterior series of scutes are connected at about the anterior region from the side of caudal peduncle of the fish body, and they completed the lateral line series of so-called “Trachura type”.
The fact that this fish has double centers in scale formation-formerly pointed out by K. IKEDA (1934)-will be quite a unique instance in comparison with that of many other Teleo-stean fishes.
When the fish reaches to about 30 mm in length, the anterior scutes develop to feather-like rhombic shape, the number of which counts 21-24, and posterior scutes develop to the caudal keel, the number of which counts 7-10. The total number of scutes of the landlocked form of this species counts 31-34.
The developmental process of the scutes of Gasterosteus aculeatus aculeatus LINNAEUS fundamentally resembles that of Pungtius pungitius (LINNAEUS), but the construction of the scutes and the number of the center of scute formation of the former are more complicated than those of the latter, because the former has many papillae on the lateral ridges and double scutes formation. This shows that this species is phylogenetically slightly apart from Genus centers inPungitius.