Aquaculture Water Quality Testing Program

- Apr 15, 2020-

Aquaculture water quality testing program

Foreword

The main chemical indicators monitored in the aquaculture industry mainly refer to the measurement of dissolved oxygen, pH, ammonia nitrogen, nitrite, hydrogen sulfide, total alkalinity, and total hardness in water bodies.

Dissolved oxygen (LDO) refers to molecular oxygen dissolved in air in water. The content of dissolved oxygen in water is closely related to the oxygen partial pressure in air and the temperature of water. Under natural circumstances, the oxygen content in the air does not change much, so the water temperature is the main factor. The lower the water temperature, the higher the dissolved oxygen content in the water. The amount of dissolved oxygen in the water is an indicator to measure the self-purification ability of the water body, and also an important indicator to measure whether the cultured water body is suitable for the growth of aquatic animals. Dissolved oxygen and food intake: Dissolved oxygen is above 5mg / L, fish eat normally; Dissolved oxygen is reduced to 4mg / L, fish intake is reduced by 13%; Dissolved oxygen is reduced to 2mg / L, fish intake is reduced 54%, growth stagnation, floating head phenomenon began; dissolved oxygen decreased to 1mg / L, fish and shrimp basically did not eat, and floated out of the water, forming a floating head phenomenon; dissolved oxygen decreased to 0.5mg / L, fish and shrimp They will all suffocate and die in a few hours.

The pH value is a value to measure the acidity and alkalinity of water, also known as the hydrogen ion concentration index. pH is an important basis for reflecting the composition and activity of algae, the stability of water quality factors and organic pollution at the bottom of the pond, and is an important indicator of water quality. One. pH affects the carbon source and the activity of trace elements in the water body, the physiological functions of aquatic animals and the biological composition of the micro-ecology, which has always been valued by farmers.

In aquaculture, the suitable pH range for most freshwater aquatic animals is 6.5-9.0, and the most suitable pH range is 7.5-8.5 for weakly alkaline water bodies. When the pH value of the water body is below 7 it is acidic, and below 5 is strongly acidic.

Mechanism and hazards of high pH value: Algae overgrowth and reproduction, consume a large amount of carbon source (carbon dioxide) in the water, causing the water body PH value to rise rapidly (the excessive growth and reproduction of photosynthetic bacteria will also cause the PH value to rise). The PH value is relatively high. Ammonium nitrogen exists in the form of ammonia molecular nitrogen in the water body, which increases the toxicity of ammonia nitrogen. In addition, the water quality with high PH value has a corrosive effect on gill tissues.

The mechanism and harm of low pH value: The water body is anoxic and the water body has too much organic matter. Under the action of anaerobic fermentation of anaerobic bacteria, a large amount of organic acid is produced, which causes the water body pH value to be low. The pH is low, pathogenic bacteria are prone to multiply, and the toxicity of hydrogen sulfide is enhanced.

Ammonia nitrogen, the normal water quality of aquaculture water is less than 0.2 mg / L. Ammonia nitrogen is mainly due to biological respiration and nitrogen source organic matter (such as bait, aquatic animal excrement, excessive fertilization, plankton corpses, etc.) under the action of microorganisms. product. Molecular ammonia is relatively toxic, while ionic ammonium is non-toxic. The ratio between the two depends on the pH value and temperature of the water. Under high pH and high temperature conditions, the molecular ammonia ratio is higher.

The symptoms caused by ammonia poisoning in fish and shrimp are different. If acute poisoning may cause shortness of breath, floating head pond, and will die quickly; if chronic poisoning, the following abnormal phenomena may occur:

May interfere with the osmotic pressure regulation system of fish and shrimp.

It is easy to destroy the mucous membrane of fish and shrimp gills.

It will reduce the oxygen carrying capacity of blood protein, which is manifested as anorexia, sideways, slow swimming, and in serious cases, swimming pools and floating heads.

Nitrite, aquaculture water requires nitrite <0.01 mg / L. Nitrite is an intermediate product of the conversion process of ammonia nitrogen to nitrate. Under anoxic conditions, it is difficult to convert nitrite to nitrate. Therefore, the accumulation of nitrite is mostly due to the low dissolved oxygen in the pond. Nitrite is highly toxic to farmed animals, and is the main factor that induces explosive diseases in farmed waters. When nitrite is poisoned in aquatic animals, it will oxidize its blood protein to form high-valent ferritin, resulting in dark blood color, which seriously affects its oxygen carrying capacity. Fish and shrimp nitrite poisoning will cause slow swimming, sideways, anorexia, swimming ponds, floating heads and other phenomena. The shrimp tail, feet and tentacles are prone to redness symptoms.

Hydrogen sulfide, aquaculture water requires hydrogen sulfide <0.2 mg / L.

Under anoxic conditions, it is produced by anaerobic decomposition of sulfur-containing organic matter in the bait or feces. Hydrogen sulfide can combine with the metal salts in the sediment to cause sulfide, which makes the sediment black. Whether the pond hydrogen sulfide exceeds the standard, the simple judgment standard lies in whether there is smell of rotten eggs in the lee of the pond. Hydrogen sulfide is highly toxic and strongly irritating. It can corrode and paralyze the gill tissues of aquatic animals and affect the respiration of aquatic animals. Shrimp hydrogen sulfide poisoning manifests as anorexia, restlessness, and swimming in the surface of the water.

Total hardness, there is no unified view or standard for total hardness. It is generally believed that in the cultivation of freshwater conventional fish, the hardness of the water body is not less than 50-150mg / L, and the suitable hardness of freshwater shrimp water body is above 250mg / L. Since the hardness of most seawater is greater than 6000mg / L CaCO3, there is generally no need to worry about the hardness of water bodies in seawater environments. According to the needs of most aquatic animals in aquaculture.

The range of total alkalinity is generally 75-200 mg / l. The minimum total alkalinity requirement for marine aquaculture shrimp is 100 ppm. It is better to increase the total alkalinity of water used for nursery to above 120 mg / l. Too low a water body has low productivity and poor buffering performance. However, the total alkalinity of the water body should not be too high, more than 500 mg / l is toxic to aquatic animals.