Observation on embryonic development of new silverfish in Taihu Lake

In order to master the artificial reproduction technology of new silverfish in Taihu Lake and improve the success rate of multiplication and release, we systematically observed the development process of fertilized eggs of new silverfish in Taihu Lake. The report of the test is as follows:

I. Materials and methods

1. Materials: the fertilized eggs of Taihu Lake New Silver Fish were collected from the artificial breeding base of Taihu Lake New Silver Fish in Xintang Bridge, Zhancheng Town, Changxing County, and the water for hatching was taken from the filtered water of 83 Reservoir.

two。 Time: April 30 to May 13, 1999, April 20 to May 15, 2003.

3. Methods: in artificial reproduction, the semen was squeezed first and then the eggs were collected, and the fertilized eggs were hatched in a petri dish. Observe, time and draw using the Olympus system Biomicroscope (BHS-313). The morphology of each stage was photographed by automatic microscope photography (PM-10AD) in time, and the samples were numbered and grouped, and the average value of the observation results was taken.

II. Results

1. Fertilized egg: the fertilized egg is light beige, nearly spherical, 0.42-0.75 mm in diameter. After fertilization, the egg expands with water, forming a perivitelline space, oocyte sedimentation, and adhering to the bottom of the petri dish with the help of free egg membrane filaments. Under the microscope, it can be seen that most fertilized eggs will not float arbitrarily because of the adhesion of the egg membrane filament, which is accompanied until the fish fry hatch.

two。 Pre-embryonic development: the water temperature was between 17.5 and 23 ℃, and the embryonic development experienced 99 hours and 30 minutes. The developmental sequence and main characteristics of each stage.

3. Post-embryonic development: the new silverfish in Taihu Lake has the following characteristics after hatching:

The main results are as follows: (1) the newly hatched larvae are 2.7 mm 3.4 mm in body length, less than 2 mm in yolk sac length, pear-shaped, 55 vertebrae and 60 vertebrae, with some brown-black pigments on the eyes and pectoral fin buds.

(2) at the beginning of the beaker, the larvae lie on the bottom of the water, turn intermittently only in place, move along a short distance after 2 hours, and swim intermittently in the water layer 4 hours later with the help of the violent swing of the pectoral fin and the torsion of the body. Later, the horizontal swimming larvae appeared, and most of the horizontal swimming larvae appeared 18 hours after emergence.

(3) in a beaker with the same number of larvae, the beaker can survive for up to 9 days without any food. 3-4 days after the yolk sac was absorbed, if the egg yolk or algae were fed, the digestive tract of the larvae showed yellow or green within 2 hours, indicating that the larvae would eat in the beaker. However, due to water pollution, the survival time of overfed larvae is shortened, and most of them live less than 9 days.

(4) after 3-4 days of hatching, the yolk sac was basically absorbed, the fins differentiated completely, and the body shape was similar to that of adult fish.

III. Discussion

1. The proportion of immature eggs is generally smaller than that of mature and fertilized eggs. Therefore, most of the immature eggs can be removed by rinsing. There is another kind of mature but unfertilized eggs, which also begin to show perivitelline space and cleavage, but they begin to whiten and blur the cell structure around 24 hours. In view of the above two situations, we think that it is more appropriate to determine the fertilization rate of Taihu Lake new silverfish in the middle and later stage of embryonic development to the progut; we should use a microscope instead of naked eye observation, hoping to draw lessons from the egg donor and egg introduction units.

two。 Because the membrane filament produced by the hatching of new silverfish eggs in Taihu Lake has a strong adhesion, and the fertilized eggs of silverfish are relatively weak, and the period from April to May is the peak feeding period of various aquatic organisms. Therefore, hatching should be carried out indoors or in reservoir cages as far as possible, such as putting it directly into the reservoir, looking for places with sufficient dissolved oxygen, no sediment erosion and less wild fish. Whether indoor or outdoor cage hatching must take into account the characteristics of great changes in day and night temperature from April to May to prevent the sudden change of hatching water temperature from suspending or abnormal embryo development.

3. According to the characteristics of late embryonic development, combined with our practice of Taihu Lake silverfish transplantation in recent years, transplanting fertilized eggs or seedlings is an optional way, and the key is to grasp the development time of fertilized eggs and seedlings during transportation. We suggest that the transport of fertilized eggs should be carried out 24 hours after fertilization, and the seedlings should be transported on the third day after emergence, so that the digestive tract of the seedlings transported to the reservoir is not long, when the seedlings have good physique and strong stress resistance. In addition, silverfish is smaller than domestic fry, and it must be smooth and fast in transportation. the density of fry in oxygenated nylon bag should not be large, which is generally controlled within 50,000 pieces per bag.

4. Whether transplanting eggs or seedlings, it is required that zooplankton are abundant, wild miscellaneous fish are few and dissolved oxygen is sufficient in the water area. Therefore, before release, appropriate fertilization should be taken in the target water area to cultivate water quality, so that the larvae can catch delicious food when they enter the water area. For the transfer of fertilized eggs, the waters with less sediment should be considered.