What are the key points for sea cucumber farming in spring?

In northern China, sea cucumber farming 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 timing of large-scale disease outbreaks in farmed sea cucumbers is basically the same, mostly from mid-February to early May in the Shandong region, 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 of rise of air temperature and water temperature 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 of the water 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 of water to remain in the upper layer and preventing it from exchanging with the bottom layer through vertical convection. As a result, the bottom layer of water on which sea cucumbers depend for survival becomes “dead water”, which prevents the abundant dissolved oxygen in the upper layer of water from being transported to the bottom layer through vertical convection.

In addition, sea cucumbers consume large amounts of oxygen through activity and metabolism at the bottom layer and through the decomposition of organic matter, while lacking timely replenishment, causing the bottom layer zone to become a low-oxygen zone, or even an oxygen-free zone. Testing shows that during this period the dissolved oxygen in the bottom layer of 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 impeded, and their stress resistance and disease resistance are greatly weakened. At the same time, anaerobic bacteria multiply in large numbers and turn to anaerobic decomposition of organic matter, 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 water in the sea cucumber pond should be increased to the maximum extent. Seize the opportunity at high tide to inject as much new water as possible into the sea cucumber pond, minimize the day-night temperature difference, and extend the flowing water time when the water temperature rises. Patrol the pond frequently and, when necessary, send divers down to the bottom of the pond to inspect the activity status of the sea cucumbers. If individual sea cucumbers are found to have skin ulceration, remove them promptly and soak them in disinfectant to prevent infection of other healthy sea cucumbers.