Timing of Crab Fry Stocking and Precautions Before Stocking
SummaryTiming of stocking crab fry: March to May is the suitable time for stocking crab fry. Precautions for stocking crab fry: choose to stock crab fry in weather that is clear, with a stable climate and little temperature variation, keep the water level at about 80cm, and the water quality should preferably be "old water"; before stocking, the crab fry should be placed in a container of aqueous solution of potassium permanganate or anti-stress drugs for disinfection.
I. Timing of Stocking Crab Fry
Spring, from March to May, is the concentrated period for releasing crab fry seedstock in both the north and the south; doing a good job of packaging, transporting and stocking the crab fry during this period is the prerequisite for the recapture rate, stable yield and high yield of adult crabs.
II. Precautions for Packaging and Transporting Crab Fry
1. When the crab fry are netted from the overwintering pond, care must be taken to wash the mud out of the crab fry's bodies and to keep the gill filaments of the crab fry seedstock moist, so as to prevent the inlet pores and gills from becoming blocked and affecting normal respiration.
2. After the net is lifted, the crab fry must not be left exposed to direct sunlight or in a ventilated state, to avoid evaporation of moisture from the gill filaments and wilting of the fry bodies.
3. Except for the lid, the insulation box must be open on all sides to maintain air permeability inside and outside the box; the crab fry inside the box must not be crowded; for cooling, use ice pops with no water leakage; according to the length of transport time, appropriately increase or decrease the number of ice pops and oxygen supply.
4. Keep the inside of the insulation box in a hibernation state of about 4℃, with sufficient oxygen, then seal the insulation box lid with tape. When loading the vehicle, leave appropriate gaps between stacked box piles, and ensure the insulated carriage has appropriate ventilation; in addition, several boxes of ice pops may be loaded and sealed as spares.
5. If the crab fry are transported continuously for more than 24 hours, sampling inspection of the crab fry survival rate is needed; for any deaths, the specific cause must be investigated item by item according to ventilation, temperature and transport duration.
III. Precautions for Stocking Crab Fry
1. Weather
Choose to stock crab fry in weather that is clear, with a stable climate and little temperature variation, to prevent a large number of crab fry from coming ashore and escaping on the day of stocking, which would affect the crab fry survival rate.
2. Water level
March to May is the suitable period for stocking crab fry; because the temperature difference between day and night is large, the crab fry are easily stimulated, so the pond water level for stocking crab fry must be kept at about 80cm, which helps reduce the stimulation of temperature differences on the crab fry.
3. Water quality
The water quality for stocking crab fry is best when it is “old water”; because the algae phase and bacteria phase of old water are stable, change little and produce abundant oxygen, it can enable the crab fry to adapt to their living environment as quickly as possible after being put into the pond, which helps raise the survival rate; at the same time, pond water polluted by domestic sewage, chemical industry water or pesticide residues must not be used for stocking crab fry.
4. Fry release method
When the crab fry are put into the pond, the correct stocking method must be adopted, commonly known as the “disinfect and spit water” method, which is to first put the crab fry into a container of aqueous solution with a certain amount of potassium permanganate or anti-stress drugs for 1-2 minutes and then take them out, wait 3-5 minutes and put them in again, for 3 consecutive times, increasing the interval by 2 minutes each time.