Fishery bulletin of the Fish and Wildlife Service - NOAA

STUDIES ON THE STRIPED BASS OF THE ATLANTIC COAST 19
In 1938 the first spawning striped bass were taken at Weldon on April 11, and by
May 10 spawning was apparently completed and the fish had left this locality. This
was an unusually early and short spawning season, probably due to the abnormally
high temperatures during this time. From April 29 to May 11 the water temperature
averaged weU over 70° F. (21.11° C.) and at one tune reached 77° F. (25.0° C.).
During the spawning season it is a quite common occurrence to see the so-called
"rock-fights" described by Worth (1903), and well known to local fishermen on the
Roanoke River. These consist of a great number of small males, 1-3 pounds in
weight, and apparently only a single female, appearing on the surface and causing a
tremendous commotion by splashing about and creating general confusion. The
activity is said to be so great that the fish often injure one another quite seriously,
and fishermen who catch striped bass when they are "in fight" attest to this fact and
to the number of small males, 10-50 as a rule, that take part in such a display with a
single female of from 4-50 pounds. Whether or not this is actually part of the spawning
act or a form of courtship does not seem to be definitely established, but general
opinion favors the former view. There can be little doubt that the spawning fish at
Weldon are composed mainly of males, the females probably never making up as much
as 10 percent of the population. In May 1938 the examination of 127 individuals
taken at Weldon showed but 6 of them to be females, and much the same sex ratio
was found to obtain farther down the Roanoke River at Jamesville, N. C., at the
same time.
There is no reason to doubt the accuracy of Worth's estimates of the number of
eggs produced by a single female striped bass. Records kept at the hatchery at
Weldon during 1928, 1929, 1931, 1932, 1937, and 1938, show that the number of
eggs per female varied from 11,000 to 1,215,000 in a total of 111 individuals examined
in this time. The majority of these fish yielded from 100,000 to 700,000 eggs each.
Unfortunately the weights of the individual fish on which these counts were made
were not taken, but a single female weighing 4% pounds, taken at Weldon on May 4,
1938, produced 265,000 eggs.
The eggs of the striped bass average about 1.10-1.35 mm. in diameter when they
become fully ripe, and at the time that they are extruded into the water. During
the first hour after fertilization the vitelline membrane expands tremendously, thus
creating a large perivitelline space. Measurements on a series of 50 eggs that were
preserved 1 hour after fertilization in a solution of 7 percent formaldehyde gave an
average measurement of 3.63 mm. in diameter, the extremes being 3.24 and 3.95
mm. Eggs similarly preserved at longer time-intervals after fertilization showed the
same general measurements. So far as one can judge from preserved specimens, the
description given by Bigelow and Welsh (loc. cit.) of the eggs as being semibuoyant
fits perfectly. These eggs are undoubtedly swept far downstream by the strong
current, and the protection against injury by jarring afforded by the large perivitelline
space is probably of no small consequence in the survival of the developing embryos.
The speed of development and the time to hatching is of course dependent on temperature.
At 71°-72° F. (21.7°-22.2° C.) hatching occurs in about 30 hours, while
at 58°-60° F. (14.4°-15.6° C.) hatching normally takes place in about 70-74 hours.
In view of the fast current in the Roanoke River, and the rate at which the developing
eggs are carried downstream, it is reasonable to assume that hatching probably does
not take place until they are close to the mouth of the river or even in Albemarle
Sound. Figure 12 shows the different stages of development of striped bass eggs and
larvae that were reared in the hatchery at Weldon, N. C. These eggs were fertilized
artificially and held at a temperature of 70°-72° F. (21.1°-22.2° C.). The photographs
of the eggs were taken from above looking down. A side, view would in reality
show that the yolk, with the developing embryo and oil globule, lies at the lower
pole of the whole egg as it floats normally in the water. The single large oil globule
which is imbedded in the surface of the yolk always lies uppermost, and the blastodisc
appears on the side of the yolk in an area that is approximately at a 90° angle with
the oil globule—not just opposite the oil globule on the lower pole as Wilson (1891)
has shown for the sea bass ("Serranus atrarius"—Wilson, loc. cit., now called Centropistes
stríatus). Hatching occurred in 30 hours in the lot under observation, and
it will be seen in figure 12 (F) that 6% days later the yolk sac was almost completely
absorbed.