| Studies on the fertilization biology of Penaeus chinensis were carried out using the method of fertilizing in seawater and in dropper from 1988 -1991. The overwinter and wild broodstocks collected from Rizhao were divided into two groups: (1) A heating group with water temperatures of up to 14 - 15°C. (2) A non-heating group (12 °C). The outside morphology and the inside structure of the sperm were observed using SEM and TEM; those of the egg were studied using the common microscopic section technique.
The results show that the ability of fertilization can preserve 3h after sperm releasing in seawater. The fertilization rate was 62.7% for the method of fertilized in seawater within 1 min after egg releasing. Maximum rates of fertilization reach more than 98%, with an average from 60% to 80% using the dropper method. On the other hand, the fertilization rate is reduced in low temperature because the sperms are not completely mature.
Sperms of P. chinensis, with a shape like a suction ear ball, are composed of two main parts: a spherical nuclear body and an acrosome. The acrosome consists of spike, an acrosomal cone, an acrosomal cap and a cap core region containing the cap core granule. The change in a fertilized sperm can be divided into 4 stages. (1) The tip of the spike expends and the vesicle is formed. (2) The vesicle expends and turns around or shrinks before dropping. (3) The acrosomal ?lament is released. (4) The front of sperm enters the egg and then the nuclear body of the sperm goes into with the vesicle.
When spawning into seawater, the egg releases the cortical rods; this cortex reaction can take place even without sperm-egg interaction. The course of the gamete interaction in the temperature of 18.5°C is: 1 min after fertilization, the egg releases cortical rods around it; after 4 - 5min, the sperm enters the egg and finishes the fertilization task; 10 min, the egg carries out the first maturation division and releases the first polar body; 25 min, the egg membrane (also called the fertilization membrane) rises up; 30 min, the second maturation division is finished, releasing the second polar body; 55-60 min, the two pronucleus combine and form a zygote nucleus; 85 min, the first cleavage is finished and forms two cleavage cells.
The maturity of the egg is physiologically reached in a very short time. During this period, some hormone is rapidly secreted in the body. With the presence of this hormone, the egg is stimulated to reach physiological maturity. The cortical reaction of eggs is not necessarily related to the fertilization. |
