The main points of raising fish in the early stage of overwintering when the water temperature is low and few fish are easy to die.

The early overwintering period of fish refers to the period from late October to early December (from Frosts Descent to heavy snow in the lunar calendar). During this period, the water temperature is low, the fish stop feeding, due to no feeding and feeding relaxation, fish have no food source, can only consume nutrients in the body to maintain basic metabolism and life activities, rapid weight loss and high overwintering mortality. Therefore, strengthening the feeding and management of fish in the early stage of overwintering can not only reduce the mortality, but also enhance the physique and disease resistance of fish, and improve the efficiency of fish culture. In the feeding and management of fish in the early stage of overwintering, the key is to grasp two aspects:

Fish breeding

First, strengthen feeding before overwintering to enhance the cold protection of fish:

At this time, the water temperature was more than 15 ℃, and the fish did not stop feeding. According to the experiment, silver carp and bighead carp have strong adaptability to low temperature, and they still eat and gain weight when the water temperature drops to 0.5 ℃ in winter, while the water temperature of grass, common carp, crucian carp and carp is about 5 ℃, that is, the water surface is not frozen, but still keeps eating and growing. In the early stage of overwintering, not only the main physiological indexes such as plumpness, tissues and organs, blood and so on remained normal, but also the average growth rate reached 12% 14%. The survival rate and profit rate per unit area in the following year were 24% and 27% higher than those in the control group, respectively. Breeders can make full use of the suitable water temperature in this period, fish strongly ingest and accumulate nutrients in preparation for overwintering, stick to feed, maintain fish weight growth and reserve enough nutrients to survive the winter, so as to improve the efficiency of fish culture. Due to the low water temperature, it is not suitable to feed cottonseed cake and pellet feed. It is better to feed powdered meal or formula feed with protein content of more than 25% and fat content of about 5%. The daily feeding amount is 0.5 per cent of the body weight of fish, or it can be fed once every 5 days. Keep throwing until the water temperature drops to about 6 ℃, and the fish basically stop eating.

Second, strengthen water quality management to create a stable living environment for fish:

At this time, the water temperature is low and the water quality is relatively stable. However, the photosynthesis of phytoplankton is weakened, the dissolved oxygen content is not high, and many harmful substances are accumulated because they can not be oxidized in time; coupled with less rainfall, the water level drops rapidly, affecting the growth of fish. Therefore, it is necessary to strengthen water quality management, and the key tasks are as follows:

1. Add new water frequently to keep the water level stable. The water level is too shallow, and the water temperature changes frequently due to the influence of air temperature, which is easy to cause cold-like symptoms in fish. In addition, due to the shrinking of the water body, the density of fish schools increases, and the concentration of metabolic waste and harmful gases increases, which does great harm to fish and is easy to cause fish species death. When the water level drops 10-15cm, new water must be injected to keep the water level stable.

2. Increase the concentration of calcium and phosphorus in water and maintain good water quality. According to the traditional culture method, there is no need to apply lime (supplement calcium) and phosphate fertilizer (increase phosphate concentration) in fishing ponds in winter. Actually this is not so. In winter, the photosynthesis of phytoplankton weakened, the carbon dioxide in the pond increased, and the pond water became weakly acidic, which endangered the physiological activities of fish and reduced the resistance of fish to adverse environment and cold. Sprinkling lime solution can not only increase calcium and promote phytoplankton to produce oxygen, but also adjust and stabilize the pH of water, which is beneficial to enhance the cold resistance and stress response of fish. At the same time, an appropriate amount of phosphate fertilizer should be applied. Because phosphorus is needed when calcium plays a role in water. The appropriate application rate of phosphate fertilizer is to keep the content of phosphate in water at 0.2 Mel 0.3 mg / L.