How to Do a Good Job in Overwintering and Seed Stock Preservation for Tilapia in Earthen Pond Aquaculture
Tilapia, commonly known as: African crucian carp, non-crucian carp, Vietnamese fish, Nanyang crucian carp, etc. Originally referring to the mouthbrooding tilapia genus fish species with Mozambique as the type locality: Mozambique mouthbrooder (scientific name: Oreochromis mossambicus), it is now a common name for several species of fish in the cichlid family, including the genera Oreochromis and Sarotherodon; in English, they are collectively called Tilapia. It is now a key research and breeding freshwater aquaculture fish in the world's aquaculture industry, and is hailed as one of the main sources of animal protein for the future. It usually lives in freshwater, but can also live in salt water of varying salinity, and can also survive in shallow water of lakes, rivers, and ponds. It has strong adaptability, can reproduce in small water areas, can even grow in rice paddies, and has extremely strong adaptability to water with low dissolved oxygen. The vast majority of tilapia are omnivorous, often eating aquatic plants and debris.
There are many methods for overwintering and preserving tilapia broodstock, but some are limited by resource conditions, such as no hot springs or no thermal drainage, and some require complex equipment and large investment. In order to explore a mass-based broodstock preservation method with low investment and simple equipment. Its main facilities and techniques are:
1. Construction of the overwintering pond: The tilapia overwintering pond should be built in a low-lying area that is sheltered from the wind and facing the sun, close to a river. In a place with firm soil, dig an earthen pond 4 m to 5 m long, 1 m to 2 m wide, and 2 m to 3 m deep. Water from the river channel can gradually seep into the earthen pond through the soil gaps, keeping the pond water fresh and the oxygen content sufficient.
2. Insulation facilities: Build a south-leaning shed frame over the pond surface with bamboo, and cover the bamboo frame with two layers of plastic film, like a greenhouse for growing vegetable seedlings. The height between the pond surface and the film should be about 0.1 m to 0.8 m; if the space is too large, it is not easy to keep warm. When the northwest wind blows, windbreak walls made of reeds or straw curtains should be placed on the west and north sides of the overwintering pond. In frost and snow weather, straw curtains should be added over the film. If a cold wave invades and the temperature drops, 2 to 4 electric lamps of 100 W to 200 W should be hung inside the plastic shed to raise the water temperature. In short, the pond water temperature should be kept at around 15°C to 16°C so that the fingerlings can safely pass the winter.
3. Putting fingerlings into the pond: Before the fingerlings are put into the pond, fill the overwintering pond with water and soak it for 3 days to 5 days to eliminate the effect of pollutants on the pond water. The time for putting fingerlings into the pond is generally in early November, when the water temperature is around 16°C; if too late, they are prone to frost damage. Before the fingerlings are put into the pond, soak them in 4% salt water for 3 minutes to 5 minutes to disinfect the fish bodies and prevent infectious diseases. The fingerling density is 5 kg to 7.5 kg per cubic meter.
4. Overwintering management: During the entire overwintering period, specially assigned personnel should manage it. At the same time, attention should be paid to changes in water temperature, changes in water quality, and the dynamics of the fish.
(1) Feeding: During the overwintering period, a small amount of feeding can be done, generally once every 10 days to 15 days, with the feeding amount at about 1% of the weight of the overwintering fingerlings, but when the water temperature exceeds 16°C, they can be fed once a day. Feed includes sugar dregs, rapeseed cake, etc. Also adjust flexibly according to the feeding situation, so that the fish eat their fill and eat well, in order to increase the overwintering survival rate and reduce losses.
(2) Lighting: Throughout the winter, as long as it is sunny, remove the straw curtains covering the insulation shed from 9:00 to 15:00 to let in light and raise the temperature. On snowy days, promptly sweep away the snow accumulated on the shed frame to prevent the frame from being crushed and collapsing.
(3) Prevention and treatment of fish diseases: The overwintering period of tilapia is relatively long, so attention should be paid to observing whether there is fish disease, and once discovered, it should be treated promptly. During the overwintering period, saprolegniasis is the most common, mostly occurring after entering the pond and before leaving the pond. Saprolegniasis is a common disease caused by the attachment of fungi such as Saprolegnia and Pythium. With the naked eye, a grayish-white, soft cotton-wool-like substance can be observed attached to the fish body. Injured fish bodies are highly susceptible to infection, and it occurs more frequently in winter and early spring. For treatment, alkaline green at a concentration of 0.1 mg to 0.2 mg/L or copper sulfate solution at a concentration of 1 mg/L can be splashed over the whole pond, which is effective. If pond hypoxia occurs and fish gasp at the surface, more fresh water can be exchanged.