Key Technical Points for Water Quality Management in Freshwater Crayfish Aquaculture
Freshwater crayfish have strong adaptability to the environment and tolerance to low oxygen, and can even directly utilize oxygen from the air. However, if crayfish are kept for a long time in environments with low oxygen and overly fertile or deteriorated water, their feeding will decline or even stop, affecting their growth. At the same time, poor water quality can also promote the massive reproduction of harmful organisms such as parasites and bacteria, leading to the occurrence and spread of diseases. When water quality is seriously poor, it can cause mass mortality of crayfish, resulting in failure of the crayfish culture. Therefore, when culturing freshwater crayfish in high-density ponds, the pond water must be adjusted in a timely manner according to seasonal changes and conditions such as water temperature and water quality, so as to create a good water environment.
Daily Water Quality Management
1. Adjusting pond water level: The water level of freshwater crayfish culture ponds is determined according to changes in water temperature, following the principle of "shallow in spring, full in summer." In spring, it is generally maintained at 0.6-1 m; shallow water is conducive to the growth of aquatic plants, the breeding of snails, and the molting and growth of juvenile crayfish. When water temperature is relatively high in summer, the water depth is controlled at 1-1.5 m, which helps freshwater crayfish get through the high-temperature season. When crayfish overwinter, the water depth of the overwintering pond should be maintained at about 1.5 m to ensure that the crayfish are not frozen to death or frostbitten. When the weather is too cold or too hot, in order to prevent the occurrence of extreme temperatures, the pond water can be appropriately deepened to stabilize the water temperature at the bottom of the pond.
2. Adjusting dissolved oxygen in pond water: Generally, the dissolved oxygen content of crayfish pond water is maintained at about 4 mg/L, which is relatively suitable for the growth and development of crayfish. Once the dissolved oxygen content is lower than 1-2 mg/L, it will cause suffocation and death of crayfish. An effective way to prevent oxygen deficiency in crayfish is to exchange water or regularly add fresh water. Generally, before May and after September, in spring and autumn, exchange water once every 10-15 days, with each water exchange amounting to about 1/3 of the pond water. In May and June, generally exchange water once every 6-7 days. In the high-temperature season from July to September, exchange water once every 2-3 days, with each water exchange amounting to 30% of the pond water. Keep the water quality "fertile, lively, tender, and refreshing," with sufficient dissolved oxygen, and control the pond water transparency at about 35 cm. Where conditions permit, an aerator can be installed in the deep-water area of the crayfish pond and operated at appropriate times to increase aeration and raise the dissolved oxygen content in the pond water. The principle for routine water addition and exchange is not to exchange water during peak molting periods, not to exchange water after rain, and to exchange more water when water quality is relatively poor. Where conditions permit, biological preparations such as photosynthetic bacteria and nitrifying bacteria can also be regularly splashed into the water to regulate the water body.
3. Adjusting pond water pH: The pH range in which crayfish can live safely is 6-9, and the most suitable pH range is 7-8.5. If the pH value exceeds a certain range--with the upper limit at 9.5-10 and the lower limit at 4-5--it will directly cause the death of crayfish. Even within the safe range, exceeding the optimal range will also have negative effects on the life activities of crayfish. To adjust the pond water pH, quicklime water can be splashed once every 15 days. When the average water depth is 1 m, use 10 kg per mu, so that the pond water pH is maintained between 7 and 8.5. At the same time, it can increase the calcium ion concentration in the water body and promote the molting and growth of freshwater crayfish.
Control Measures for Poor Water Quality
During production, if water quality deterioration is found and phenomena such as freshwater crayfish coming ashore, climbing, or even dying occur, the following measures must be taken promptly to adjust water quality:
1. First exchange part of the old water, splash the water body with bromochloro hydantoin at 0.3 mg/L for disinfection, then add fresh water.
2. On the second day, splash zeolite powder at 20 mg/L and Yishuibao (Bacillus subtilis) at 0.4 mg/L.
3. After that, regularly splash microecological preparations into the water body about every 5 days. Use beneficial bacterial preparations to form dominant bacterial flora to inhibit the population size, growth, reproduction, and harmfulness of pathogenic microorganisms, decompose harmful substances in the water, increase dissolved oxygen in the water body, and improve water quality. Application of photosynthetic bacteria, nitrifying bacteria, Bacillus, Bifidobacterium, yeast, etc., can all produce the above effects.