Practical Water quality Control Technology in Aquaculture

Water is the living environment of aquaculture animals. Water quality directly affects the growth and development of fish, shrimp, crab and other aquatic animals, which is related to the yield and economic benefits of aquaculture. Therefore, it is very important to regulate and control water quality in the process of aquaculture production. Our aquaculture production must adjust the water quality with reference to mature and quantified indicators to meet the needs of aquatic animals for different physical and chemical factors in the water body to the maximum extent, so as to promote their growth and development and achieve our ultimate goal of aquaculture production.

In the process of aquaculture production, the physical and chemical factors that affect the growth and development of aquaculture objects in the water environment are mainly dissolved oxygen, pH, ammonia, nitrite, hydrogen sulfide and so on. These factors are constantly changing with the change of water temperature, bait feeding, metabolism and photosynthesis of aquatic animals and plants. In order to obtain good benefits, these physical and chemical factors must be controlled.

1. Dissolved oxygen

Aquatic animals must live under aerobic conditions, and hypoxia can cause them to float their heads and die. Therefore, dissolved oxygen is one of the life elements of aquatic animals.

1.1 requirements for dissolved oxygen in aquaculture water:

Generally speaking, the dissolved oxygen in aquaculture water should be kept at 5-8mg/L, at least above 4mg/L. If the dissolved oxygen is low and light, it will slow down the growth, be prone to disease, and die of floating head if it is heavy, while too high dissolved oxygen will cause fish bubble disease.

1.2. Causes of insufficient dissolved oxygen

① temperature: the solubility of oxygen in water decreases as the temperature increases. In addition, high oxygen consumption of aquatic animals and other organisms at high temperatures is also an important reason.

② culture density: the greater the stocking density in the pond, the greater the biological respiration and biological oxygen consumption, so it is easy to lack oxygen in the pond.

③ organic matter decomposition oxygen consumption, the more organic matter in the pool, the more active bacteria, this process usually consumes a lot of oxygen to carry out, so it is easy to cause hypoxia in the pool.

Oxidation of ④ inorganic substances: when there are low-oxygen inorganic substances in water, oxidation will occur and consume a large amount of dissolved oxygen. As a result, the amount of dissolved oxygen in the pool is reduced.

1.3. Response of fish, shrimp and crab to hypoxia

When there is mild hypoxia, the fish and shrimp will be restless, the fish will float, the shrimp will tend to the side, the crab will come ashore, breathe faster, eat less or stop feeding; in severe hypoxia, it will lead to the death of fish, shrimp and crabs, resulting in losses. If the water in the pond is in a state of insufficient dissolved oxygen for a long time, the growth of aquatic animals will stop.

1.4. Relationship between dissolved oxygen and other toxic substances

Maintaining sufficient dissolved oxygen in water can inhibit chemical reactions that produce toxic substances, such as ammonia, nitrite and sulfides, such as ammonia and hydrogen sulfide after decomposition of organic matter in water; in the presence of sufficient oxygen, ammonia is converted to nitrous acid and then to nitric acid, and hydrogen sulfide is converted to sulfate, resulting in a non-toxic end product. Therefore, it is very important for aquaculture to maintain enough dissolved oxygen in aquaculture water. If there is a lack of oxygen, these toxic substances can easily reach the harmful level quickly.

1.5. How to increase oxygen

The best and most convenient way is to inject new water. If possible, an aerator can be used to increase oxygen. Oxygen enhancer can be used in case of lack of conditions or emergency. Using oxygen enhancer can increase oxygen at the bottom of the water body and purify water quality at the same time.

2. PH (pH value)

PH value is an important index for measuring water quality, this is because fish, shrimp and crabs have their own pH adaptive range, and pH determines many chemical and biological processes in water, such as ammonia and hydrogen sulfide. Due to different forms of pH value, the degree of toxicity is also different, so pH value is a barometer of water quality.

2.1. Ph value control standard of water quality

Biological photosynthesis, respiration and all kinds of chemical changes in water can cause the change of pH value, and its change has a great impact on fish, shrimp and crab and water quality. The pH value of freshwater culture should be kept between 7 and 9.

Direct effect of 2.2.pH value on aquatic animals

PH value is too high or too low to aquatic animals have direct damage, and even death. Acidic water (pH value)