First, the selection of ponds and preparation for aquaculture is crucial. Typically, shrimp farming ponds or reservoirs with an area of over 30 acres are chosen, with a depth of at least 1.5 meters and steep walls to prevent erosion. The pond bottom should be firm to avoid sediment disturbance. If the slope is too gentle, a fence should be installed at a depth of 0.5 meters along the shore, and a 10 cm mesh sieve should be placed 30 cm above the water surface. This net helps prevent sea otters from getting stuck in shallow areas due to wind or water currents.
Wild fish and crabs are major predators of jellyfish and must be removed before stocking. The first water filling is usually 10 to 20 cm, followed by a lime (100 kg per mu) or bleach solution (30 ppm) treatment to disinfect the pond. Inlet and outlet pipes should have screens with 40–60 mesh to prevent wild fish and other predators from entering. As the jellyfish grow, the mesh size can be adjusted accordingly.
Jellyfish primarily feed on small zooplankton, so maintaining a rich plankton population is essential for their survival and growth. About 10 days before stocking, fertilizer should be applied. Typically, 300 kg of fermented chicken manure is added per acre, and if needed, nitrogen and phosphate fertilizers in a 10:1 ratio can be used to supplement nutrients.
Before stocking, it's important to test the physical and chemical parameters of the water. The ideal temperature range for sea otters is 15°C to 34°C, with the best growth occurring between 18°C and 28°C. Salinity should be between 8‰ and 37‰, with optimal levels around 16‰ to 28‰. The pH should be between 7.5 and 8.5, and no harmful pollutants should be present.
There are three main methods for obtaining seedlings. The first involves capturing natural larvae from the sea. The second method is semi-artificial, where mature sea otters are harvested and artificial bases are used to collect larvae. The third is fully artificial, using adult clams or cultivated ones to produce high-quality seedlings through intensive breeding. Seedlings are ready for stocking when they reach 1.5–2 cm in diameter.
When transporting seedlings, only healthy and active individuals with closed central mouths and umbrella diameters over 2 cm should be selected. Short-distance transport can use containers without oxygenation, while long-distance transport typically uses oxygenated plastic bags. For seedlings with a 2 cm diameter, the density should be 600–700 per liter. If the journey exceeds 5 hours, cooling and reducing density are necessary to improve survival rates. Light conditions during transport should also be carefully managed.
The number of sea otters stocked directly affects their growth, as plankton biomass is a key factor. In commercial farms, about 27 individuals per mu are commonly harvested, with an average weight of 5–10 kg and a maximum of 15 kg. Depending on the survival rate of different-sized seedlings, stocking density varies. Young seedlings with a 2 cm diameter are typically stocked at 250–300 per mu. Staggered stocking and rotation help maximize pond usage and economic returns.
When planting seedlings, the water level should gradually increase to more than 1.5 meters, and water clarity should be maintained at around 30 cm. Instead of manual feeding, maintaining a high zooplankton concentration is critical. Organic fertilizers like fermented chicken manure are applied 2–3 times monthly at 100 kg per mu. Inorganic alternatives such as urea (1–2 kg/mu) and superphosphate (2–4 kg/mu) can be used if organic options are unavailable.
As sea otters grow, especially after one month, their water quality requirements become stricter. Delayed water changes can lead to poor conditions and mass mortalities. Daily water exchange should be 10–20%, with a tide of at least 30%. However, water changes are not recommended during the first 10 days. Sea otters tend to float in the morning and evening, so regular checks of water quality, plankton levels, and growth should be conducted. 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 cause rapid changes in water chemistry, leading to reduced survival rates. These challenges remain a key issue that requires further study and management strategies.
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