Efficient Fish-Clam Polyculture Methods and Key Technical Points

In 2004, I conducted a pond fish-clam polyculture experiment and achieved relatively good economic benefits. The farming details are described as follows.

I. Experimental Materials

1. Preparation of farming ponds Two standard ponds excavated from low-lying fields were selected (having been@#@233@#@for three years), with a total area of 10.2 hectares, pollution-free, facing the sun, well ventilated, oriented north-south, rectangular in structure, with an average water depth of about 2 m. Water intake and drainage were convenient, with abundant water sources and good water quality.

2. Pond clearing and disinfection One week before stocking fish and clams, on a sunny day, 75 kg of quicklime per mu at 1 m water depth was used for pond clearing and disinfection, and 200 kg of fermented chicken manure per mu was applied to build up adequate base fertilizer and cultivate good water quality. Fingerlings were strictly disinfected before stocking, nets and various tools were used exclusively in each pond, and feeding grounds were regularly disinfected with bleaching powder. ⟧7⟧ 3. Suspended culture of pearl mussels In February 2004, 1000 two-year-old triangle sail mussels (Hyriopsis cumingii) per mu that had been implanted with mantle pieces, were strong in constitution, and free of disease were suspended for culture. A hanging net-clip method was adopted for pearl mussel culture. In polyethylene flat net clips measuring 15 cm x 40 cm with a mesh size of 3 cm x 3 cm, pearl mussels were placed with the foot pointing downward, 3 mussels per net clip. Generally, in spring and autumn the net clips were suspended in water about 15 cm below the surface, while in winter and summer they were appropriately suspended deeper, about 35 cm below the surface.

3. Suspended Culture of Pearl Mussels In February 2004, 1000 two-year-old triangle sail mussels (Hyriopsis cumingii) that had been implanted with mantle pieces and were strong and free of disease were suspended in culture per mu. The pearl mussels were cultured using the net-clip hanging method. In flat polyethylene net clips measuring 15 cm x 40 cm with a mesh size of 3 cm x 3 cm, the mussels were placed with their feet pointing downward, 3 mussels per net clip. Generally, in spring and autumn the net clips were hung in the water at a depth of about 15 cm below the surface, while in winter and summer they were hung somewhat deeper, at about 35 cm below the surface.

4. Fingerling stocking In late February 2004, 20 bighead carp, 30 silver carp, 20 grass carp, and 50 crucian carp with strong constitutions were stocked per mu. In April of the same year, 150 white fish and 120 flower bone fish were stocked per mu. In May of the same year, 10 mandarin fish (body length 2.5 cm) and 0.75 kg of large-sized berried shrimp (caught from the mussel pond) were stocked per mu. Among these, mandarin fish and berried shrimp were stocked once each year.

II. Feeding Management

1. Feeding and fertilization At the water inlet, along the pond bank, a fine mesh cloth was used with the pond ridge as one side to enclose a circle in parallel at a distance of 1 m, and the enclosure was used to pile fermented organic fertilizer. In seasons with lower temperatures, part of the fermented manure, mainly chicken manure, was applied in a timely manner, with small amounts applied multiple times, generally twice a month. From March to August, when temperatures were relatively high, chemical fertilizers were applied, adhering to the principle of small amounts applied multiple times, generally 1 kg of urea and 3 kg of superphosphate per mu. Pond water transparency was controlled at about 25 cm. White fish and flower bone fish were fed artificially by broadcasting special pellet feed for white fish and through domestication. The pellet feed had a protein content above 35%, and feeding adhered to the "four fixed" principles. Under normal weather, pellet feed was fed twice daily, once from 8 to 9 a.m. and once from 4 to 5 p.m. On rainy days or when air pressure was low and the weather was muggy, feeding was postponed or stopped. The daily feeding rate was controlled at 5% of fish body weight in the early stage and 3% in the later stage.

2. Timely water filling Pond water was often kept in a slightly flowing state. Generally, water was flushed once every 10 days, and the water exchange volume was required to reach about 50 cm depth. In summer and during disease outbreaks in fish and clams, water was changed once every 7 days, so that the water body reached a state of being "fertile, lively, tender, and refreshing."

3. Frequent application of quicklime Each month, 15 kg per mu of quicklime per meter of water depth was dissolved in water and splashed over the entire pond once (it could not be splashed on the net cages), and from May to September it was required to be splashed 2 to 3 times per month. If large areas of green algae appeared in the water body, quicklime application was temporarily stopped.

4. Timely inspection and good record-keeping On the basis of good morning and evening pond patrols, pearl mussels were sampled and inspected once each day, and pearl mussels were regularly turned to prevent the formation of yin-yang surfaces on the pearls on the left and right sides and to prevent mussel shells from becoming stuck in the net lines, and attachments on the net cages were removed in a timely manner. During seasons with high incidence of mussel disease, timely inspections were made, dead mussels were removed and the pearls inside were taken out, so as to reduce cross-infection of mussel diseases caused by dead mussels.

III. Results

Harvest was carried out on January 20, 2006. A total of 1.123 million yuan was invested (including 206,500 yuan for pond rent, 495,300 yuan for pearl mussels, 48,500 yuan for fingerlings, 156,000 yuan for feed, and 125,000 yuan for hired labor wages), the total output value was 1.8835 million yuan, the total profit was 760,500 yuan, and the input-output ratio was 1:1.68. The fish and clam harvest details are shown in Table 1.

Table 1 Fish and Clam Harvest

Name Pearl mussel Mandarin fish White fish Flower bone fish Freshwater shrimp Other

Yield (kg) 18152617151253050158916530

Survival rate (%) 83958792

Output value (10,000 yuan) 119.86.5533.289.156.3513.22

IV. Reflections

1. The fish stocking combination structure must be reasonable. Fish-mussel polyculture is a farming model mainly based on pearl mussels, and the total fish yield must be controlled. The yield of conventional fish is generally required to be within 150 kg per mu. In terms of fish species, because silver carp and pearl mussels have similar feeding habits, they should be stocked appropriately less. Black carp, triangular bream, and common carp easily cause rotten foot disease in pearl mussels, so they should not be stocked. Polyculturing new species such as white fish and flower bone fish and feeding pellet feed is a good exploration and development direction for optimizing the fish-mussel polyculture model, but problems such as slower growth of white fish and flower bone fish in mussel ponds than in specialized ponds and low utilization rate of pellet feed are relatively prominent.

2. Frequent application of quicklime Calcium is an indispensable substance in the growth process of pearls. After March, pearl mussels begin to carry eggs. Applying more quicklime can inhibit their reproduction and is beneficial to the formation and growth of pearls.

3. Rotational harvesting of fish According to the growth of fish and shrimp, ground cages, shrimp cages, and other gear can be used to harvest and market them at the proper time, harvesting the large ones and leaving the small ones. On the one hand, this can use seasonal differences in fish prices to improve economic benefits, and on the other hand, it can reduce farming density and promote the growth of fish and mussels.