Key points of bottom algae cultivation techniques in mudskipper aquaculture

Bottom algae cultivation techniques for mudskipper aquaculture. The feeding habit of the mudskipper (Boleophthalmus chinensis Osbeck) is mainly benthic diatoms, followed by blue-green algae. When feeding, it presses its lower jaw against the mud surface and moves its head from side to side, scraping the epibenthic bottom algae on the mudflat as food; it does not directly feed on rice bran, soybean cake, peanut cake and other feeds. Therefore, when carrying out artificial aquaculture, bottom algae must be cultivated to form an algal pasture to provide food for the mudskipper.

1. Pond preparation Fish ponds are generally 1.5-15 mu, as too large a size is difficult to manage. Soft clay is best for the pond bottom, and the pond bottom should be flat. The pond bottom should be higher than the low tide line of the sea area, so that the water can be drained to sun-dry the flat, and the pond depth is 50-80 cm. Dig a cross-shaped trench in the center of the pond, and open a ring-shaped edge trench along the pond edge, forming a ""-shaped trench; the trench area accounts for about 10% of the pond area, the trench width is 2 m, and the trench depth is about 30 cm. Around the pond, set up an escape-prevention net (nylon screen) about 60 cm high. Set a sluice gate on the side of the pond facing the sea and connect it to the central trench; both the pond bottom and the pond trenches slope toward the gate. Set up escape-prevention facilities at the water inlet and outlet.

2. Killing of enemies The main enemies harmful to the cultivation of algal pastures are saltwater snails (sea snails), saltwater centipedes and chironomid larvae (red worms), which must be killed. For the first two, 0.3 mg/L of molluscicide or 1000 kg of tobacco sand per hectare can be applied for control. For the latter, 0.25 mg/L of Lebaycid or 0.3 mg/L of Sumithion can be used to drive them out.

3. Bottom algae cultivation Choose clear weather, drain the pond water, and expose the pond bottom to the sun for several days until it cracks; then apply 400 kg of manure, 200 kg of rice bran and 20-50 kg of calcium carbonate per hectare. When applying fertilizer, it should be evenly splashed over the pond bottom and no heaps should form. Then, fill with brackish water (specific gravity 1.01-1.02) and maintain a water depth of 15 cm. To promote the growth of diatoms, water glass (containing 27% sodium silicate) at 30 mg/L and ferric trichloride at 3 mg/L can be splashed at the same time. After 3-5 days, the bottom algae gradually multiply and form an algal bed, and then fry can be stocked. The algal bed formed is best when it consists of brown diatoms and relatively tender blue-green algae.

4. Intermediate management After the bottom algae are cultivated, mudskipper fry can be released. At this time, the water depth should be maintained at about 15-20 cm, and the water quality should be kept clear so that sunlight can penetrate to the pond bottom, favoring photosynthesis by the algae and accelerating the development and reproduction of the bottom algae. After more than half a month of rearing, the originally cultivated bottom algae can no longer meet the growth needs of the fish in the pond, and the water quality has begun to gradually become turbid. At this time, the water can continue to be drained to sun-dry the flat for 3-6 days, but the water depth in the ring trench should be maintained at 15-20 cm to provide shelter for the mudskipper. After that, additional fertilization is carried out. There are three additional fertilization measures: (1) 1.75 kg of urea, 0.5 kg of superphosphate and 0.1 kg of water glass per mu. (2) Spread 10 kg of rice bran per mu. (3) Apply 140 kg of chicken and duck manure plus 0.1 kg of water glass per mu. At the same time, introduce brackish water to promote the reproduction and development of the bottom algae again. In this way, repeat the operation to keep the bottom algae growing luxuriantly and provide food for the mudskipper to forage.

5. Precautions 1 During the intermediate management process, when sun-drying the flat, the size of the mudskipper fry should be considered. For fry smaller than 5 cm, it is not suitable to sun-dry the flat. Therefore, the size of the fry stocked should be considered in terms of whether they can reach more than 5 cm by the first sun-drying of the flat after stocking. 2 When applying fertilizer, the manure should be splashed as much as possible on the surface of the cracked bottom mud to prevent it from flowing into the mudskipper's burrows and poisoning the mudskipper. 3 To accelerate the formation of the algal bed, seawater with richer nutrients and abundant diatoms and blue-green algae can be introduced, and artificial inoculation can also be used. 4 When planning to sun-dry the flat, pay attention to the weather forecast; otherwise, if it rains, the algal bed will be washed away.