Home >> Papers-from-the-department-of-marine-bio-volume-11 >> Properties Of Photogenin And to With Special Reference To_2 >> The Breeding Season

The Breeding Season

eggs, days, june, females and stages

THE BREEDING SEASON.

The limits for egg-laying by the gaff-topsail at Beaufort can not be set very narrowly, but an attempt will be made to indicate when males with eggs may be taken. This research was initiated the first week in August 1906, but only females long spent were taken. The real search for the fish was begun in 1907, when the first female was captured on June 4. Her ovary had in it no eggs over 10 mm. in diameter, but did show a lot of recently evacuated follicles. On June 6, other females were brought in having ova as large as 20 mm. Plainly, the breeding season was not over.

As explained before, it was found impracticable to search for the breeding males in 1907 until June 22, and the eggs taken on this day had on them young in various stages, but the majority had the whole yolk covered with the blood vascular system.

The search for early stages of the eggs began in 1908 on June 3. On this day a female with empty follicles was taken, as were others two days later. Notwithstanding daily seinings, no eggs were taken until June 11, and constant inquiries brought no news of the finding of a single egg by any of the fishermen before this date. Our failures, as explained elsewhere, were due to the freshening of Newport River by heavy rains. The youngest of these eggs had the yolk circulation covering quite half of the egg and were at least 10 days, probably 2 weeks old.

In 1909, the first eggs were taken May 27. These had on them forming embryos with a huge open blastopore behind. They were probably from 5 to 7 days old. However, a number of females were taken having enormous bellies due to the greatly swollen undischarged ovaries. A number of these females were brought to the laboratory in a live-car and kept in the turtle pound. Four days later the largest of these was spawned artificially and gave up 68 grown eggs.

In 1910, the first eggs were taken May 21, before my arrival. These were few in number and low in vitality, whether because they were naturally infertile or because they had not been fertilized could not be determined. On May 25 we were fortunate in getting males with eggs in early invagination stages. These were probably 3 to 5 days old. On the following day more eggs of about the same stage were taken.

In 1911, as noted elsewhere, two trips were made to Beaufort for gaff-topsails. Having always been too late for early stages hereto fore, I went too soon this year. The first seining was done May 13 and 40 or 50 huge females were taken, but from none of them could eggs be obtained. A large number of males was also caught but not one had the depressed hyoid region indicative of the breeding season.

On May 15 a number of large females were obtained but none would give up eggs. The males, however, of this day's catch had enlarged oral cavities ready to receive eggs. None of these females had genital orifices markedly reddened. This spring was a late cold one and had evidently delayed the spawning beyond the normal time.

My second trip in 1911 gave me a seining on May 25. From this were obtained the youngest eggs ever gotten in this research—eggs with the invaginating edge of the blastoderm placed equatorially. Here again I was too late for segmentation stages, the eggs having been laid in my absence. However, they could hardly have been more than 3 days old.

The breeding season is plainly determined by the stage of ripeness of the eggs and this is pretty definitely fixed by the temperature. With a warm spring, egg-laying comes earlier, with a cold one later; but the evidence seems to be that once the laying begins it is quickly concluded. Normally this breeding season, as indicated by the data above given, begins about May 18-20, and rarely extends over 10 days, probably being concluded in even less time. This is plainly evidenced by the difficulty in finding early stages, and further by the fact that the majority of eggs taken in any season at any time are all about the same stage.

There must now, however, be given some data which contrasts markedly with the foregoing. On July 21, 1910, there were brought to me, by fishermen in Newport River, 2 male catfish with eggs and larva in their mouths. The 5 larvae had their yolk-sacs four-fifths closed over by the body-walls and were able to swim freely and actively.

The 28 eggs had on them embryos which were just beginning to show dark stippling on the dorsal parts, and were plainly from two to three weeks younger than the larvae above described. This is a remarkable case. The eggs were of a late laying. With this case another must be correlated. On June 8, 1910, I took a female having ovarian eggs 7.5 to 8 mm. in diameter. These might have possibly come to maturity and would then have been extruded to give late embryos like those described above. This certainly would have been the case with the female having ovarian eggs of 20 mm. on June 6, 1907. These cases are, however, isolated ones among scores and even hundreds of normal ones, and are probably instances of extreme variation. On page 36 it is noted that the 28 eggs above referred to were markedly smaller than the normal ones.