How to Prevent Moss in Crab Ponds? Key Points for Prevention and Control in Crab Farming

The massive growth of moss in crab ponds has an enormous impact on the survival rate of river crab seedlings and farming profitability. The main reasons for moss spreading in crab ponds are:

(1) Relatively shallow water levels and strong light. During the germination and early growth stages of aquatic plants, to ensure the plants receive enough light for normal germination and growth, crab farmers usually keep the water level at 10-20 cm. Maintaining a low water level for a long time will lead to moss outbreaks.

(2) There is a large amount of moss in the water source. When water is let into the crab pond, moss in the water source enters the pond with the water flow and multiplies in large quantities.

(3) Heavy fertilization. When farmers find that aquatic plants are not growing as well as desired or that moss has already appeared, they use heavy fertilization to enrich the water; after fertilization, moss grows faster until it overruns the entire pond.

(4) Overfeeding. During river crab farming, too much feed is given, and the leftover feed settles at the bottom of the pond and, after fermentation, causes moss to breed.

(5) Incomplete pond clearing. If moss damage occurred in the crab pond the previous year, and the pond was not cleared or sun-dried before crab farming the following year, the incidence of moss is very high. In addition, the indiscriminate use of drugs to prevent crab diseases causes water quality pollution, and excessive application of ammonium bicarbonate, phosphate fertilizer and unfermented organic fertilizer damages the ecology of the crab pond; or moss is brought into the crab pond when transplanting aquatic plants, all of which can cause moss to overrun.

After moss has grown massively, because a large amount of aquatic plants in the crab pond need protection, the commonly used copper sulfate and herbicide-containing drugs are restricted in use, and manual removal often accelerates the spread of moss; therefore, moss control should focus on prevention. Common preventive measures include:

(1) Dry the pond and expose it to the sun for more than 1 month before planting aquatic plants and stocking crab seedlings.

(2) When clearing the pond, dissolve 1.5 kg of copper sulfate per mu in water and sprinkle it evenly over the pond bottom and pond slopes; after 3-5 days, apply 100-150 kg of quicklime per mu of crab pond, slaked into a slurry, and splash it over the whole pond to neutralize the copper sulfate.

(3) When planting aquatic plants, apply 3-5 g of urea per cubic meter of water to promote the growth of aquatic plants, moderately enrich the water, and prevent moss from occurring.

(4) After planting aquatic plants, use a low water level to promote germination, and raise the water level in a timely manner as the aquatic plants grow; in the Yangtze River basin, the pond water level should be no less than 40 cm in mid-to-late April and no less than 60 cm in mid-May.

(5) Apply fermented organic fertilizer or bio-organic fertilizer.

(6) Feed reasonably to prevent excess feed; the feed must be kept fresh.