In aquaculture, the selection of ponds plays a crucial role in ensuring successful sea otter farming. Typically, shrimp breeding ponds or reservoirs with an area of over 30 acres are chosen, as they offer easy access for water intake and drainage. The depth should be at least 1.5 meters, with steep walls and a firm bottom. If the pond slope is too gradual, a fence should be installed at a depth of 0.5 meters along the shoreline, and a 10 cm sieve screen should be placed 30 cm above the water surface. This net helps prevent sea otters from getting stranded in shallow areas due to wind, waves, or water currents.
Before releasing sea otters, it's essential to eliminate wild fish and crabs, which are natural predators. The first water filling is usually around 10–20 cm. Lime (100 kg per mu) or a bleach solution (30 ppm) is applied across the entire pond. Inlet and outlet channels must be equipped with screens of 40–60 mesh to block unwanted organisms and protect seedlings during water exchange. As the sea otters grow, the mesh size can be adjusted accordingly.
Jellyfish primarily feed on small zooplankton, so the availability of plankton directly affects their survival and growth. To ensure sufficient nutrients, fertilization is carried out about 10 days before seeding. Organic manure like fermented chicken dung (300 kg per acre) is commonly used. Depending on the water quality, supplementary nitrogen and phosphorus fertilizers (in a 10:1 ratio) may also be added.
Before stocking, water quality parameters such as temperature, salinity, and pH should be tested. Sea otters thrive best in temperatures between 15°C and 34°C, with an optimal range of 18°C to 28°C. Salinity should be maintained between 8‰ and 37‰, ideally 16‰ to 28‰. The pH level should remain between 7.5 and 8.5, with no signs of pollution.
There are three main methods for obtaining sea otter seedlings: capturing wild juveniles, semi-artificial cultivation by attaching them to substrates, and fully artificial breeding using cultivated clams. Seedlings are ready for release when they reach 1.5–2 cm in diameter.
When transporting seedlings, only healthy and active ones with closed central mouths and umbrella diameters over 2 cm should be selected. Short-distance transport can use smooth-walled containers without oxygenation, while long-distance transport typically involves oxygenated plastic bags. For seedlings with a 2 cm diameter, the density should be around 600–700 per liter. If the journey exceeds 5 hours, cooling and reducing density are necessary to maintain survival rates.
Stocking density varies depending on seedling size and survival rate. Young seedlings with a 2 cm diameter are usually stocked at 250–300 per mu. Rotational stocking is recommended to optimize pond usage and increase economic returns. When the external temperature stabilizes above 20°C, choose sunny and calm days for planting. Seedlings should be placed in the morning or evening to avoid direct sunlight.
Upon arrival at the pond, the seedlings should be gradually acclimated. First, the bag is opened to observe vitality, then the seedlings are transferred to a larger container for 10–20 minutes. They are then carefully placed into the pond using a boat or by submerging the bag in the water. If no boat is available, seedlings can be placed on the pond’s edge, but the process must be slow to avoid damage.
After stocking, the water level should be gradually increased to over 1.5 meters, and the water clarity should be maintained at around 30 cm. Zooplankton is the primary food source, so maintaining high plankton levels is essential. Organic fertilizers like fermented chicken manure are applied 2–3 times a month, at around 100 kg per mu. Inorganic alternatives like urea and superphosphate can be used if organic options are unavailable.
As sea otters grow, especially after one month, water quality becomes more critical. Delayed water changes can lead to poor conditions and high mortality. Daily water exchange should be 10–20%, with a tidal exchange of up to 30%. However, the first 10 days should avoid frequent water changes to allow the ecosystem to stabilize.
Sea otters tend to float in the early morning and late afternoon. After release, regular checks on water biomass, quality, and sea otter growth are necessary. Any larvae found in shallow areas should be returned to deeper waters.
During summer, when temperatures exceed 28°C, evaporation increases, and sudden rain can alter water chemistry, leading to reduced survival rates. These challenges require further research and management strategies to maintain healthy populations.
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