What are the causes of autumn deaths in river crabs?

Death from cold

In autumn, the temperature difference between day and night is large, sometimes reaching about 10°C, and river crabs find it hard to adapt, which triggers colds, leading to loss of appetite, difficulty breathing and death. Prevention methods: usually pay attention to adjusting the water level and controlling drastic changes in water temperature; when adding new water, the temperature difference should not exceed 3°C; grow more covering plants such as water hyacinth and alligator weed on the water surface (no more than 1/2 of the water surface). When the weather changes, appropriately deepen the water level.

Indigestion

Due to changes in air pressure and water temperature, river crabs are very prone to indigestion and death. Control methods: first, change the water quality and regularly disinfect with limewater; second, regularly add antibiotics and growth hormones to the food; third, do not feed or feed less plant-based bait, and increase animal-based bait, especially high-protein bait such as earthworms and river snails; fourth, feeding must be done at fixed times and in fixed amounts, and when the water temperature drops, appropriately reduce the amount of bait.

Natural death

As the saying goes: “When the autumn wind rises, the crab's legs itch.” Every year from September to November, a batch of river crabs that have grown for 2 years shed their shells and change from “yellow crabs” into “green crabs,” entering the final stage of life. Because these river crabs have reached sexual maturity, the osmotic pressure inside their bodies rises, and they cannot adapt to the low-osmotic-pressure freshwater environment, so they often die naturally. Farmers should catch and sell these river crabs in time to avoid affecting profits.