Fishery bulletin of the Fish and Wildlife Service - NOAA

STUDIES ON THE STRIPED BASS OF THE ATLANTIC COAST 31
lateral fields at the focus. (See fig. 15.) Scales from striped bass that were beyond
their fifth year were not used, since the annuli were often indistinct and it was therefore
difficult to make precise measurements. Van Oosten (1929), Greaser (1926),
and others have pointed out that the validity of the scale method of determining the
length of a fish at different years in its life depends on 3 main factors: (1) That the
scales remain constant hi number and identity throughout the life of the fish; (2)
that scale growth is proportional to the growth of the fish; and (3) that the annuli
are formed yearly and at the same time of the year. Since it has been proved in
many other species that scales do maintain their identity throughout the fife of the
fish, and because there is no evidence to the contrary hi the striped bass, it has been
assumed that the first requirement holds true. In testing the relation of scale
growth to the growth of the fish, the radii of scales from 153 bass of measured length
RELATIONSHIP OF SCALE GROWTH.
TO GROWTH OF STRIPED 8ASS /
LENGTH OF FISH IN CMS
FIGURE 21.—The relationship of scale growth to body growth in the striped bass (see Table 16 lor original data).
from 10.5 to 67 cm. were plotted against the lengths of the fish. (See fig. 21.) It
will be noted that there is a good straight-line relationship, and that therefore the
scale growth may be considered proportional to the growth of the fish within the
limits studied. There is no proof, however, that scale and body growth are proportional
m the smaller sizes below 11 cm., or in the extreme larger sizes above 67
cm. The formation of annuli has already been discussed, and there can be no doubt
that they are formed yearly and at the same time of year—during the winter.
Since all the larval stages of development of the striped bass were not available,
it was impossible to determine the factor С (that length at which scales first appear
on the fish) by careful examination of preserved material. Bass down to 2.0 cm.
were collected in the field, and these all showed prominent scales. Individuals up to
0.5-0.6 cm. (approximately 8 days after fertilization of the eggs and 6 days after
hatching) were preserved from the hatchery at Edenton, N. C., and these did not show
any signs of scale formation. It was therefore necessary to estimate at what length
scales first appear on striped bass between 0.6 and 2.0 cm. by other means. The
material that forms the basis of figure 21 was used for this purpose. A regression
equation expressing the body-scale growth relationship of the striped bass was
277589—41 3