Technical communication

Why is your fish pond starved of oxygen?

The dissolved oxygen of fish pond generally comes from three aspects, one is the photosynthesis of phytoplankton; The oxygen diffused in the atmosphere and dissolved in water; The third is artificial mechanical flushing or application of oxygen, three to photosynthesis oxygen.

At the same time, the consumption of ecological dissolved oxygen in the pond is mainly manifested in three aspects, one is the dissipation of physical action to air; The second is the chemical reaction of some substances in water and consumption; Third, the respiration of aquatic organisms, organic decomposition, substrate and other biological effects of consumption. The oxygen consumption of fish is related to the species, age, weight, sex and activity level of fish, as well as water temperature, dissolved oxygen, carbon dioxide, pH value and other factors. So how to analyze and judge the fish pond hypoxia and carry out effective regulation?

Lighting effects
Due to the influence of light intensity, the upper water of the pond generally has a higher light intensity in the daytime, so phytoplankton photosynthesis is stronger and dissolved oxygen is higher. However, the lower layer of water is not easy to convection due to the weakened illumination intensity and thermal resistance, and the lower the dissolved oxygen is. Especially in high temperature season, the difference between upper and lower water temperature is great, and the dissolved oxygen in the bottom water is very little. Meanwhile, the dissolved oxygen level in the water varies greatly between day and night. At night, the water temperature in the upper layer of the water decreases gradually with the decrease of the air temperature, and the density increases, resulting in density flow. The dissolved oxygen in the middle and lower layer of the water is replenished slowly, while the dissolved oxygen in the upper layer decreases gradually, until it reaches the lowest level in the early morning. In addition, under the influence of different wind directions in the same pond, the dissolved oxygen in the water is also in an unbalanced state. During the day, there is always more oxygen produced by phytoplankton and dissolved into the air downwind than upwind, and the greater the wind, the greater the difference in dissolved oxygen content up and down. At night, on the contrary, because there are more plankton and organic matter in the downwind than in the upwind, the oxygen consumption at night is high, so the dissolved oxygen in the upwind is more than that in the downwind.

Seasonal climate change affects water dissolved oxygen is closely related to seasons and climate, especially in the summer and fall, the water temperature is higher, bait casting quantity increase, due to the accumulation of waste and the bait fish, leading to lower pond water low dissolved oxygen, water and sediment microbes and phytoplankton due to a lack of oxygen metabolism is restrained, lead to the underlying dissolved oxygen at very low levels. In addition, the light intensity of plum rain season is weak, and the photosynthesis of aquatic plants is poor, which can easily cause water hypoxia. At the same time, in terms of weather, such as the summer evening thunder shower, the weather is overcast, or in the continuous rain low air pressure, wind, fog, etc., or long sunny rain, fish feed, water quality, once the weather changes, all can cause lack of oxygen, especially in the summer sometimes more dramatic changes in the weather, easy to cause water in great changes of dissolved oxygen.

It is a complex system for free-stocking and inputs to affect water bodies. There are various kinds of free-stocking breeding species, feed bait, fertilizer, fishery medicine, etc., plus a large number of plankton, benthic organisms, aerobic bacteria and other respiration, as well as their excreted feces and other organic matter decomposition process, which all need a large amount of oxygen. And the dissolved oxygen in the pond water will be different because of the biological and physical and chemical factors, so the change of dissolved oxygen level in the pond is very complex. In addition, if the fish pond is injected with toxic sewage or due to improper fertilization, too much unfermented organic fertilizer is put at a time. Decomposition in the fish pond consumes a large amount of oxygen and releases toxic gases, worsening the water quality, which will also cause hypoxia, and even cause 'pan pond' dead fish in serious cases.
Look at the weather: according to the weather forecast and the day of the weather forecast, such as sudden changes in the weather or continuous cloudy and rainy, we should pay attention to the occurrence of hypoxia.

Look at the season: the summer feeding intensity is large, the water temperature is high, the probability of hypoxia is larger. Or the plum rain season or seasonal alternation when the temperature difference is large should pay close attention to the dissolved oxygen.

See water color: water color is thick, transparency is small, such as weather changes, easy to cause a large number of plankton death, water oxygen consumption increases, can cause hypoxia.

Observation and ingestion: when inspecting the fish feeding grounds, it is found that the feed is not finished within the specified time, and there is no disease, indicating that the dissolved oxygen level in the fish pond is low.

See floating head: fish often because water quality is too fat, sultry weather and anoxic floating head, cause dead fish phenomenon extremely easily. Fish floating head has the weight of the points, the general morning floating head is flirtatious head, the middle of the night began to float head for heavy. The floating head is lighter in the pool, while the floating head around is heavier. Slightly disturbed fish on the sinking light, scared after the fish did not respond heavy.
Changes in fish ponds Control measures of fish pond dissolved oxygen filling regularly new water under the condition of high density cultivation, residual bait in the fish ponds, dirt is more, anaerobic fermentation to produce ammonia, hydrogen sulfide and other harmful substances, deterioration of water, especially the high temperature in summer season, the water quality changes quickly, so periodic water flooding is the most commonly used to adjust water quality is one of the most economic and applicable method. In general, add new water once every 7 ~ 10 days, and add water 15cm ~ 20cm each time. When the pool water deteriorates more seriously, it is advisable to adopt water changing measures to maintain good water quality conditions. For ponds dominated by silver carp and bighead carp, the water color should be g RASs green or brown with a transparency of 20cm ~ 30cm. The ponds with g RASs and carp as the main ones are lighter than those with silver carp and bighead carp. The fresh water should be filled once every 7 ~ 10 days, and the water level should be raised by 15 ~ 20 cm each time. In summer, fish ponds should be kept at maximum water level.

Stir the bottom mud regularly. Stir the bottom mud can promote the decomposition of the bottom material and indirectly control the change of water quality. Generally stirring once every 10 ~ 15 days, each stirring area is not less than 1/3 of the water area, and the stirring effect is best in sunny days at noon, but do not stir when the weather is sultry and low pressure.

The aerator should be equipped with a special aerator, of which the impeller type is the best. When the aerator is turned on, it can make the water convection, increase the dissolved oxygen in the water and emit toxic gas. Pay attention to turn it on at noon on sunny days, in the morning on cloudy days and at midnight on rainy and cloudy days. Generally, it can be turned on for oxygenation at 2 ~ 3 noon in sunny days, and it can also be turned on for oxygenation when there is floating head danger.

Water quality testing equipment is used to focus on monitoring dissolved oxygen. Conventional monitoring methods can only be used for monitoring water intake at fixed points on time, and cannot reflect the specific situation of the whole water body, especially the bottom water body. The index of the bottom water determines the condition of the whole aquaculture water. At present, online monitoring equipment has become the mainstream monitoring method, which can monitor water quality indicators in real time and give early warning when hypoxia occurs.

PREVIOUS：Feasibility of factory shrimp farming NEXT：The reliability of yellow catfish culture usi