Cortical reaction and solicitation mechanism in Hemibarbus labeo ovum

Abstract

There are 1 to 4 rows and five types of cortical alveoli in the cortex of the pallas (Hemibarbus labeo) egg. From the outer to the inner of the cortex, the diameter of the cortical alveoli decreases gradually. We found a new structure named solicitation speckle at the low latitude of the animal pole and near the micropylar apparatus between the ovum envelope and cell membrane in the zygote of fish. The solicitation speckle similar to type I cortical alveoli was very purple in H.E chromosome, and it had no obvious boundary with the ovum envelope and membrane. Moreover, no membrane around the solicitation speckle in TEM was found. In SEM, the solicitation speckle looked flocculent. During cortical reaction, the solicitation speckle played a very important function in arousing cortical reaction. Thirty-five seconds after fertilization, cortical alveoli began to break down near the low latitude of the animal pole. At the same time, the same thing happened near the micropylar apparatus before cortical reaction. Both starting points encountered and healed up at the vestibule of the micropylar apparatus. The cortical reaction that happened near the low latitude of the animal pole was another new pattern. The cortical reaction was divided into four parts that included latent period, developmental period, climactic period and declining period. In the latent period, no cortical alveoli were released. In the developmental period, a few cortical alveoli were released outside the cortex. In the climactic period, several cortical alveoli were inosculated into a big vesicle and released intensely. In the declining period, the type V cortical alveoli and the other remnant cortical alveoli were released. Five minutes after fertilization, cortical alveoli were released entirely in the animal pole. Five minutes after fertilization, all of the remnant cortical alveoli were released. This leads us to conclude that cortical reaction is induced by type I cortical alveoli, and the solicitation speckle is a volcanic chain reaction under water or the other lower osmotic pressure of fluids. The outer cortical reaction can accelerate the inner cortical reaction. While cortical alveoli releases in batches, the cell plasma membrane is reorganized over and over. No cortical alveoli were found below the micropylar tube where sperm enters the ovum, which suggests that the cortical reaction prevents polyspermy.

Sexual Dimorphism and Discrimination of Barbel Steed (Hemibarbus labeo) in the Jinhe River, China: An Indicator of Habitat Status

“…Owing to environmental pollution, overfishing, and other factors, there has been a sharp decline in the wild resources of H. labeo in many rivers. The artificial breeding of H. labeo has been performed in different regions, such as the Fujiang, Wusuli, Yalu, Liaoning, Oujiang, and Qiantang Rivers, to save this precious resource [21][22][23][24][25]. Moreover, H. labeo has the wide distribution, medium life span, the fast growth rate, high fertility, early sexual maturity, and benthic nature.…”

“…The population ecology of H. labeo in many water bodies has been studied, including the Heilongjiang Basin [20,23], the Yangtze River Basin [21,22,27,28], the Pearl River Basin [26] in China, Chikugo River in Japan [29], and Goe-san Lake in Korea [30]. In a study of the reproductive biology of H. labeo in the Ganjiang River of China [27], we observed that the morphological differences between wild female and male individuals are not apparent.…”

“…In a study of the reproductive biology of H. labeo in the Ganjiang River of China [27], we observed that the morphological differences between wild female and male individuals are not apparent. For example, the characteristics of the female cloaca protruding outwards [23] are not evident, and the annual sexual maturity of H. labeo populations in the Ganjiang River is not synchronized [27]. Generally, adult male H. labeo fish have a similar abdominal bulge as adult female fish because of the large amount of food consumed during the breeding season [27].…”