Techniques for Using Biogas Residue and Biogas Slurry in Loach Farming

1. Site Selection and Pond Construction

Choose a spot behind or in front of a house where the water source is reliable, drainage and irrigation are convenient, it is sheltered from the wind and faces the sun, and it is close to the outlet of a biogas digester. The size of the pond can be adapted to local conditions; generally, an area of 10-20 sq m is suitable, with a pond depth of 1.2 m. The pond walls should be built with lime or bricks, and the surface should be smoothed with cement. Special water inlet and outlet should also be built, with wire mesh fitted at the inlet and outlet to prevent the loaches from escaping. A shade shed should be built above ground, and an insect-attracting lamp should be installed.

2. Pond Clearing, Disinfection and Stocking of Loach Fry

Using 0.22 kg of quicklime per cubic meter of pond water, slake the quicklime into a slurry and, while it is still hot, splash it evenly over the whole pond for disinfection. Test that the pond water pH has dropped below 7, or observe that water fleas are active, or place several dozen loaches in a bundled box installed in the pond water for trial rearing; if the loaches live normally in the box for one day, the fry can be stocked. Both artificially bred and wild loach fry can be used for rearing. The fry should be uninjured, disease-free, physically strong and lively. Before stocking, soak them in a 3%-4% salt solution for 8 minutes. It is suitable to stock 80-100 loach fingerlings of 3-4 cm per sq m. The stocking sizes should not differ too much, so as to avoid the big ones eating the small ones.

3. Rational Feeding and Timely Water Changing

The loach is an omnivorous fish. During the rearing process, in addition to applying biogas residue and biogas slurry to cultivate natural plankton feed, suitable amounts of palatable snails, earthworms, as well as bean curd residue, rice bran, distillers' grains and tender plant stems and leaves can also be fed. The daily feeding amount as a proportion of the total body weight of the loaches is: 1% in March, 4% in April-June, 10% in July-August, and 4% in September-October. Feeding should adhere to the four fixed principles: set up a feeding platform in the pond and place the feed on the platform; fixed times, feeding once each morning and evening every day; fixed location, the feed in the pond should be fresh and free of rot and mold; fixed quantity, with the amount eaten within 2-3 hours after feeding being appropriate. Biogas residue and biogas slurry should be applied alternately according to the pond water quality. Apply 250 g of biogas residue per sq m each time, and 500 g of biogas slurry per sq m each time, once a week. During the rearing cycle, turn on the insect-attracting lamp at night to attract insects as supplementary feed for the loaches. Also frequently observe changes in the pond water quality; generally, yellow-green water is suitable. If loaches are seen jumping out of the water surface, it indicates the pond water is too fertile and the water is short of oxygen, so new water should be added in time and the old water released. Especially in muggy or thunderstorm weather, pay even more attention to frequently adding new water and aerating in time. If conditions permit, an aerator can also be installed to increase oxygen and prevent loach deaths.

4. Disease Prevention and Control and Prevention of Predators

Common diseases include saprolegniasis and fin rot. Diseased loaches can be soaked in a 10-15 micrograms/mL antibiotic solution for 10 minutes, or the whole pond can be splashed with bleaching powder (containing 25-30% available chlorine) at a concentration of 1×10-6. Common parasites include trichodinids and tongue cup worms. These parasites attach to the fry and can cause death. Diseased fish will show symptoms such as increased mucus on the body surface, swimming alone away from the group, floating on the water surface, and reduced appetite. At this time, the body surface mucus of the diseased fish should be promptly examined under a microscope; if about 50 trichodinids or tongue cup worms are observed in a low-power field of view, the whole pond can be splashed with 0.7×10-6 copper sulfate. For predators such as rats and snakes, patrol the pond frequently to prevent them.