What are the key management points for the middle and late stages of shrimp farming?

In the middle and late stages of shrimp ponds after the body length reaches 7-8 cm, due to increased feed input, shrimp excrement gradually accumulates, and together with dead algae, residual feed, and the oxidative decomposition of organic matter at the pond bottom, the pond water quality, substrate, microorganisms, and so on have undergone great changes.

@#@234@#@The specific changes in the water environment and shrimp in the middle and late stages are: pH gradually rises, the water color changes from clear green and yellow-green to brown and tea-green, transparency decreases, and turbidity increases; the pond bottom turns black and has a foul odor, and the number and types of harmful microorganisms increase; the tail fan and antennae of the shrimp turn red, and even tail rot and broken antennae occur. In some shrimp ponds, shrimp grow slowly, have weak constitutions, poor sensitivity, incomplete molting, ciliate parasitism, poor feeding, and enteritis and yellow gill disease appear; moreover, in some shrimp ponds, symptoms such as shrimp swimming along the pond, floating head, soft shell, red legs, rotten eyes, and shell ulcers occur. Based on years of experience in shrimp farming, the author summarizes the key management points for the middle and late stages of shrimp farming.

Stabilize the water color and reduce water turbidity. The reason for the change in pond water color in the middle and late stages of shrimp farming is mainly insufficient magnesium ions needed for the reproduction and growth of green algae. Spraying dolomite powder at 20-25×10-6 once every 7-10 days can stabilize the water color. To reduce water turbidity, apply photosynthetic bacteria at 10-15×10-6 and spray the whole pond once every 7 days. At the same time, insist on regular disinfection of the aquaculture water, disinfecting the whole pond twice every 10-15 days. For the first time, spray the whole pond with dibromohydantoin disinfectant in the morning at the treatment concentration; for the second time, spray the whole pond with organic iodine and quaternary ammonium salt at 0.2×10-6 in the morning of the next day. If there is a lot of suspended organic matter in the water and turbidity is high, the disinfectant concentration can be appropriately increased.

Regulate the balance of nutrient salts in the aquaculture water environment and supplement the calcium, magnesium, and phosphorus content in the water. Every 10-15 days, spray the whole pond with 2-3×10-6 calcium hydrogen phosphate once and 20×10-6 dolomite powder once.

Improve the pond substrate environment and control pH. Every 10-15 days, spray beneficial microbial preparations at 0.3×10-6 once, or every 5 days spray a substrate improver mainly made of zeolite powder once, with each application amount of 10-15×10-6. If sudden heavy rain or continuous overcast days cause the pH to drop below 7.5, spray the whole pond with quicklime at 5-8 kg per 667 sq m.

Add and exchange water reasonably. On the first day, control the water exchange amount at about 10 cm; on the second, third, and fourth days, gradually increase the water exchange amount to 20 cm, 30 cm, and 50 cm. In this way, it can both improve water quality and promote shrimp molting and growth. If the water level is insufficient, deepen the water level in time and purchase aeration equipment so as to increase aquaculture output and scale. Facts have shown that the higher the shrimp farming output and the larger the size, the more obvious the economic benefits.

Feed reasonably and reduce the feed conversion ratio. Generally, feed 4 times a day. The morning feeding time must be arranged 1-2 hours after the sun rises, and it is best when dissolved oxygen in the water reaches 4 mg per liter or more. After that, feed once every 6 hours. Control the feeding amount well; generally, it is appropriate for the shrimp to finish the feed within 45 minutes to 1 hour.

Improve shrimp immunity and stress resistance. Add to the feed: immune polysaccharide 1‰, biologically active enzyme additive 2‰, vitamin c 1‰-2‰, vitamin b1 0.5‰, and feed continuously for 2 days each week, 2 meals per day; in high-temperature seasons, add allicin 0.5‰-1‰.

Regularly sample and inspect the health status of the shrimp. If shrimp are found to eat less feed or diseased shrimp float at the head and stay near the edge, generally the infection rate of shrimp diseases in the pond has reached more than 20%. Therefore, for diseased shrimp that have been infected but still feed normally and do not float at the head or stay near the edge, treatment measures should be taken in time. In the middle and late stages of shrimp farming, generally every 3-5 days, a cast net with a relatively fine mesh must be used to randomly sample 200-300 shrimp around the pond to observe whether they are normal. When shrimp suddenly increase or decrease feed intake, during periods of sudden climate change such as after heavy rain or wind, and after water intake or water exchange, and in other situations that may induce shrimp disease, use a cast net to sample and inspect as soon as possible.