Abstract
Morphological changes accompanying the growth of the shortspine spurdog,
Squalus mitsukurii (Squaliformes: Squalidae) were examined in ten specimens of 304.1 to
952.6 mm in total length (TL), collected from Sagami and Suruga bays, Japan. The caudal
fin of specimens less than 330 mm TL has a broad white margin on the upper lobe, and the
lower lobe is overall white. The upper lobe changes from having a rounded tip to a pointed
tip at total lengths between about 450 to 500 mm, and the white posterior margin of the
caudal fin also narrows in specimens of this size. The dermal denticles on the anterior part of
the first dorsal fin in smaller specimen are arranged with a space between each one, bearing
a tricuspid leaf-like portion and a stalk at the base. On the other hand, the dermal denticles
change to a rhomboidal shape and become arranged in a muriform pattern without spaces
between them in larger specimens. In comparison with Squalus sp. 2 specimens less than
324.1 mm TL, it is suggested that S. mitsukurii specimens of the same size are distinguished
in having the second dorsal spine less covered with dermal denticles.
