On resting zones found on the cross-section of fin-rays of some fishes

Abstract

On cross-section of dorsal fin-rays of Caprodon schlegeli (GUNTHER), Sardinia melanosticta (T. & S.), and Scomber japonicus HOUTTUYN, resting- zones are found. The cross-sections are made by ordinary histological method embeding in paraffin after decalcification by 10% nitric acid diluted by 10% formalin, stained with Delafield's Hamatoxylin, Mayer's Satires Hamalaun, and Hamatoxylin-Eosin, and cut out in 8-10 microns by means of a mlcrotome. The resting zones of S. melanosticta appear stained deeply by Hämatoxylin (Fig. 2, B), and those of S. japonicus found stained light violet (Fig. 2, C). The growth zones of S. japonicus appear dyed light red. But those of C. schlegeli are very indistinct (Fig. 2, A).
The number of the resting zones and the growth-ratio between the resting zones occuring on the cross-sections of the fin-rays appear to be largely corresponding to those found on the scales in, at least, S. melanosticta and S. japonicus (Tables 1-4). But this trait seems to be less valuable for the purpose of fishery-biology of such fishes given above by the reasons given below, viz, it is difficult by the present method to make the cross-section for study of a large number of individuals of the fish for which observations may be done, and in addition to this no standard point available for measurments useful for back-calculation of body-length is present.