What are the reasons for fewer diseases in polyculture of fish and shrimp?

1 Polyculture area and species

The total polyculture area of Pacific white shrimp with milkfish and male tilapia was 400 mu. A total of 330,000 milkfish fry were stocked, with 200 mu for polyculture of Pacific white shrimp and milkfish, 120 mu for polyculture of Pacific white shrimp and male tilapia, and 80 mu for milkfish monoculture as a control.

2 Pre-stocking work

Before releasing the fry, pond clearing, pond drying and disinfection were carried out according to routine procedures. Seawater was introduced in a timely manner, and fertilizer was applied to cultivate basic bait organisms.

3 Stocking density and stocking period

The number of fry to be released can be determined according to the pond conditions, management level, and the specific situation of aerator equipment. In the milkfish monoculture pond (control pond), an average of 2,000 fry were stocked per mu; in the polyculture pond, an average of 20,000 Pacific white shrimp fry and 850 nursery-grown fry were stocked per mu. The Pacific white shrimp fry were stocked in mid-April. The milkfish were stocked on May 15.

4 Water quality management

Water was added regularly, mainly freshwater. According to changes in water color, fertilizer was appropriately applied or water was exchanged to keep the water color yellow-green, green or yellow-brown, so that the water maintained rich microbial bait organisms, but not overly dense.

5 Do a good job of bait feeding

During the polyculture of male tilapia and shrimp, only shrimp feed was always provided. Milkfish and tilapia mainly fed on leftover shrimp feed, shrimp excrement, and various benthic organisms and algae. However, they also consumed a small amount of shrimp feed. The feed conversion ratio for shrimp was 1.3.

6 Do a good job of disease prevention

During the culture process, disinfection and application of water quality improvers were carried out regularly. The specific practice was as follows: 15 days before releasing the fry, 50 kg of quicklime was spread per mu along with 25 mg/kg tea seed cake water. After splashing to kill miscellaneous fish, fenvalerate was used to eliminate miscellaneous shrimp, and then seawater was introduced to 60-70 cm for fertilizing the water. Throughout the entire culture process, disinfection and application of water purifiers were carried out once every 15 days, and medicated feed was also provided at the same time.

7 Timely harvest After 100 days of culture, the Pacific white shrimp reached the commercial size of 60 shrimp per kg, and harvesting began with electric nets. High-yield ponds reached 225 kg per mu, low-yield ponds reached 100 kg per mu, with an average yield of 140 kg per mu. The selling price was 15-16 yuan per kg, and the output value per mu ranged from 3,000 to 7,200 yuan. The milkfish and male tilapia were left in the pond to continue being cultured until harvested at 120-150 days, with about 500 kg of fish produced per mu. The survival rate reached 90%, and monoculture reached 1,000 kg per mu.