Detailed Explanation of Spring Precautions for Sea Cucumber Farming

Sea cucumber farming in the north is mostly open-air farming in tidal flats and shrimp ponds with artificial reefs. Many farmers hold the notion that because winter temperatures are low, sea cucumbers need no management, which leads to the death of many sea cucumbers. Based on what has been learned in recent years, the periods when large-scale disease outbreaks occur in farmed sea cucumbers are basically the same, mostly from mid-February to early May in the Shandong area, concentrated in March and April.

The important changing factor during this period is that air temperature and water temperature gradually rise from the severe cold of the winter low-temperature period, but the rates at which air temperature and water temperature rise are different: air temperature rises quickly while water temperature rises slowly, with a lag phenomenon. When air temperature exceeds water temperature, a water temperature difference forms between the middle-upper layer and the bottom layer in such farming ponds, creating water temperature stratification. Measurements show that the temperature difference at a water depth of 1 m to 3 m is 1°C to 2°C. Water with a higher temperature has lower density and lower specific gravity, causing the upper-layer water to remain in the upper layer and preventing it from exchanging with the bottom-layer water through vertical convection. As a result, the bottom-layer water on which sea cucumbers depend for survival becomes “dead water”, so the ample dissolved oxygen in the upper-layer water cannot be transported to the bottom layer through vertical convection of the water.

In addition, sea cucumber activity at the bottom, metabolism and the decomposition of organic matter consume large amounts of oxygen, while timely replenishment is lacking, turning the bottom zone into a low-oxygen zone or even an oxygen-free zone. Testing shows that during this period the dissolved oxygen in the bottom-layer water is mostly below 3 mg/L. Under low-oxygen or oxygen-free conditions, the metabolic level of sea cucumbers declines, the functions of the circulatory, nervous, digestive, respiratory and other systems are impaired, and their stress resistance and disease resistance are greatly weakened. At the same time, anaerobic bacteria multiply in large numbers, turning into anaerobic decomposition of organic matter and producing highly toxic harmful substances such as ammonia nitrogen and hydrogen sulfide, further intensifying the adverse effects on sea cucumbers. Because of the deterioration of water quality, sea cucumbers become weak in constitution, and various bacteria and other pathogens take the opportunity to invade, causing sea cucumbers to become diseased.

To prevent the above situations from occurring, the actual exchange volume of the water body in the sea cucumber pond should be increased to the greatest extent possible; when the tide is high, as much new water as possible should be injected into the sea cucumber pond; the diurnal temperature difference should be minimized as much as possible; and when the water temperature rises, the flow-through time should be extended. The pond should be patrolled frequently, and when necessary, divers should be sent to inspect the activity status of the sea cucumbers on the pond bottom. If individual sea cucumbers are found to have skin ulceration, they should be promptly removed and soaked in disinfectant solution to prevent infection of other healthy sea cucumbers.