Dissolved oxygen and fish farming

Dissolved oxygen in water is closely related to the growth of fish, mainly reflected in three aspects. 1, the source of dissolved oxygen in water: 1 dissolved from the air. 2 Photosynthesis of plants. 3 supplement water and oxygen. Usually, the photosynthetic oxygenation rate in the still water pond is about 89%; the dissolved oxygen in the air is about 7%; the hydration and oxygenation is about 4%. Aquaculture fish ponds are mainly supplemented with water and oxygen. 2, the consumption of dissolved oxygen in water: generally to the fish's breathing, water breathing (plankton, phytoplankton, bacteria and other respiratory oxygen consumption), bottom oxygen consumption (benthos, organic matter decomposition, the more the end of fat and oxygen consumption More), into the air (fish pond oxygen saturation, will escape to the air oxygen) and other oxygen-consuming. In general, the oxygen consumption of fish accounts for about 5%-15%; the escape air accounts for about 1.5%; the remaining 80%-90% are mostly water respiration and oxidation of sediment and oxygen consumption. 3, the dissolved oxygen in water changes: 1 surface water dissolved oxygen diurnal changes very large, generally from the afternoon to sunset before the maximum oxygen content, the whole night after sunset to the lowest value before sunrise. The more water is fattened, the more phytoplankton in the water, and the greater the change in day and night. Especially in summer, dissolved oxygen in surface water can reach supersaturated state, but dissolved oxygen will be reduced to the lowest value from night to sunrise, which often causes fish to “float”. 2 In the deeper surface of the fish pond and the bottom water layer, there is a “temperate layer”. When there is no wind stirring to break this layered state, the upper layer of water is often rich in oxygen and the bottom layer is deficient in oxygen. According to the law of vertical distribution of dissolved oxygen, the oxygen aerator is opened for a period of time at noon every day to allow the surface and bottom water to mix, which is beneficial to oxygen storage during the day. In short, the maximum value of dissolved oxygen in fish ponds usually appears in the surface water layer in the summer afternoon. If there is excessive feeding and fertilizer, the water in the pool is too fat, the stocking is too dense, the bottom sludge is thick, and the weather is hot and the pressure is low. Cause whole pool hypoxia. Once the lack of dissolved oxygen in the water, it will make the fish's ability to decline, loss of appetite, increased feed coefficient, physical decline, increased disease. Therefore, the appropriate dissolved oxygen index can not be based on whether the fish is floating head, but should be to ensure the normal physiological needs of the fish such as appetite and exuberance. The rich dissolved oxygen is conducive to the conversion of organic matter in water into various nutrients absorbed by food organisms. According to China's fishery water standards, in more than 16 consecutive hours, it must be greater than 5 mg/l for more than 16 hours and no lower than 3 mg/l for any time. . Therefore, reasonable stocking, feeding and fertilization should be used to remove the silt, ensure the quality of water, and prevent fish from lacking oxygen and suffocation.

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