Technical communication

Aquaculture talk about ammonia nitrogen changes color, but not all ammonia nitrogen is toxic you know?

Nitrogen exists in water as nitrogen, free ammonia, ionic ammonium, nitrite, nitrate, and organic nitrogen.

Free ammonia and ionic ammonia are collectively called ammonia nitrogen. Ammonia is a common problem in aquaculture water especially in high density intensive ponds. It has brought great harm to breeding production.

【 Reason analysis 】 Only nitrogen in the form of NH4+, NH2- and NO3- in water can be used by plants. So both of these are beneficial.

Other forms of nitrogen in the water cannot be used by plankton and can be harmful to fish.

[Solution]

(1) Source of ammonia nitrogen in water The ammonia nitrogen in the pond mainly comes from three ways, namely the excrement of aquatic animals, applied fertilizer, feed and excrement decomposed by microorganisms and animal and plant residues.

Fish can discharge ammonia nitrogen into the water through their gills and urine, and crustaceans can discharge ammonia nitrogen into the water through their gills and antennal glands.

Aquatic animal feces and animal and plant residues contain a large amount of protein, which is decomposed by microorganisms in the pond to form amino acids, and then further decomposed into ammonia nitrogen. At this time, a biological filter can be used to remove ammonia nitrogen.

(2) Mechanism of ammonia nitrogen poisoning Increased ammonia nitrogen in water can inhibit the excretion of ammonia in fish, increase the concentration of ammonia in blood and tissues, reduce the oxygen-carrying capacity of blood, and increase the concentration of carbon dioxide in blood.

NH3 is not charged, has high lipid solubility, and is easy to directly cause fish poisoning through the cell membrane, resulting in breathing difficulties, increased secretion and death of fish failure.

NH3 can cause damage to gill epidermal cells and reduce the immunity of fish.

(3) Harm to fish caused by "nitrogen-rich" in water Bodies The main substances harmful to fish in water bodies are ammonia nitrogen and nitrite. China's water quality standards stipulate that ammonia concentration is less than 0.5 mg/l, nitrite concentration is less than 0.2 mg/l, biofilter can play a very good role.

1) Ammonia nitrogen in water is toxic to fish ammonia nitrogen consists of NH4+ and NH3, among which NH3 is toxic to fish and NH4+ is not toxic to fish.

The percentage of both in ammonia nitrogen is determined by pH value, temperature, salinity and other factors. The increase of pH value, temperature and salinity will lead to the increase of NH3 proportion in ammonia nitrogen and aggravate the toxicity of water to fish.

The lethal concentrations of NH3 for silver carp fry and bighead fry were 1.106 mg/l and 0.559 mg/l for 24 hours and a half, respectively. With the growth of fish, the lethal concentrations of ammonia gradually increased.

The concentration of NH3 which can inhibit the growth of g RASs carp is 0.099 ~0.455 mg/l, and the maximum allowable concentration of NH3 is 0.054 ~0.099 mg/l.

The maximum allowable NH3 concentration of hybrid tilapia is 0.035~0.171 mg/l. Concentrations of NH3 in excess of 0.66 mg/l are toxic to carp species.

In general, species of the same fish have less ammonia tolerance than adults. Different fish have different tolerance to ammonia nitrogen.

The tolerance of wheat tassel is the worst, and the bearded catfish is relatively strong. Therefore, the scaleless fish is the dominant fish group in the river where "ammonia water" is often discharged.

2) Symptoms of acute ammonia poisoning ① Fish floundering and swimming, and sometimes sinking, lying on the side, spasm and other symptoms.

② Shortness of breath, mouth sometimes open. The gill cover is partially open, and the gill filaments are purplish black, sometimes bleeding. (4) Fin strip stretches, base bleeding, body color becomes shallow, and body surface mucus increases.

(4) Prevention and control of "nitrogen rich" in water bodies

1) Reducing feed conversion ratio (FCR) Feed is the main source of nitrogen in water. Reducing nitrogen excretion from fish by improving feed quality and reducing feed conversion ratio (FCR) is the main measure to prevent and control "rich link" in water.

Specific measures are: accurate determination of fish requirements and the content of available amino acids in feed; A balanced diet based on digestible amino acid content was prepared to meet the needs of fish.

Metabolic regulator such as enzyme preparation, organic acid preparation and so on to improve the utilization rate of amino acid and phosphorus; Reduce the adverse effects of anti-nutrient factors in feed to improve feed conversion and reduce nitrogen excretion rate.

In addition, scientific feeding standards can reduce the amount of residual bait, which can reduce the nitrogen content of water.

2) The serious imbalance of the ratio of nitrogen and phosphorus in the culture of phosphorus with nitrogen in water can cause a large amount of nitrogen can not be used by phytoplankton, resulting in the formation of "nitrogen-rich" and harmful to fish.

Due to the use of high protein feed in intensive fish ponds, the nitrogen content in the water is very high. The ratio of nitrogen and phosphorus in water body can be reduced to a more suitable level by applying phosphate fertilizer.

This has enabled the plankton population to nearly double, and a significant increase in readily digestible algae. But when phytoplankton die, ammonia levels in the water suddenly rise.

Because the ammonia in the water comes not only from fish, but also from dead phytoplankton released by bacteria, the phytoplankton can't really remove nitrogen from the water.

3) Improve water body by planting aquatic plants Aquatic plants such as duckweed and phoenix eye lotus can be appropriately planted in the aquaculture water body, and the ammonia absorbed by these plants will leave the water body at the same time when they are harvested.

4) Increase the dissolved oxygen pool in water, especially the dissolved oxygen at the bottom of the pool, can make the toxic ammonia nitrogen, nitrite content of water drop, hydrogen sulfide is eliminated, and the PH value of water quality is stable.

5) The use of biological filters, pure oxygen dissolved oxygen device, normal manufacturers of ammonia nitrogen reduction drugs will also have an obvious effect on improving water quality.