"My goldfish is congested, what's going on?"My guppies are in the tank, what's the matter?.""My angelfish died violently, why?"”Aquarists often have similar doubts. While there are many causes of fish illness or death, poor water quality is one of the most common. There is a saying in the aquaculture industry that "fish are raised before water". As the saying goes, "the soldiers and horses have not moved, the grain and grass go first", the first step in fish farming is not to buy fish, but to raise water. Water is to fish what sunlight and air are to people, and its importance is self-evident. As long as the water is well maintained, the fish will naturally get sick less. But do you know what water cultivation is?And how to raise water?This article can help you understand the purpose and principle of water farming and realize the freedom of fish farming.
The two "best killers" in water - ammonia nitrogen and nitrite
The fish food we feed and the metabolites produced by the fish (such as feces, etc.) are decomposed by microorganisms and bacteria in the water body, and the organic matter will produce a toxic substance - ammonia nitrogen in the decomposition process. Ammonia nitrogen is broken down by nitrosifying bacteria to form less toxic nitrite. China's "Fishery Water Quality Standards" stipulates that the mass concentration of ammonia nitrogen and nitrite in aquaculture water should be less than 0 respectively2 mg l and 01 mg l, too high a concentration of the two can cause fish poisoning or even cause "group extermination". Some studies have pointed out that the ammonia nitrogen concentration of grouper fry is greater than 4The environment of 74 mg L showed symptoms of irritability and fright, severe cases struggled violently in the water, the body bent and spasmed, and the dorsal fin and pectoral fin opened when dying, the gill cover was slightly opened, and the body color turned whiteIn the environment where nitrite concentration was greater than 200 mg L, the fry would have rapid breathing, black body color, and death of poisoning after 4 h. Low concentrations of ammonia nitrogen and nitrite can also inhibit the immunity of farmed animals, thereby increasing the risk of disease outbreaks.
The "nemesis" of ammonia nitrogen and nitrite - nitrifying bacteria
Ammonia nitrogen and nitrite are the main culprits in the water that make fish sick or die, and nitrifying bacteria can be used against these two guys.
Nitrifying bacteria refer to a class of microorganisms that can convert toxic ammonia and nitrite into non-toxic nitrate, and obtain energy from this oxidation process to assimilate carbonate (CO32), bicarbonate (HCO3) and carbon dioxide (CO2) to synthesize cellular matter, which belongs to chemoautotrophic bacteria. It can be seen that the great thing about nitrifying bacteria is that they form an ecosystem, the so-called nitrification system, to naturally decompose harmful substances in water. According to research reports, regular addition of photosynthetic bacteria, lactobacilli, yeast, bacillus, nitrifying bacteria and other microbial agents to the aquaculture water can effectively reduce the concentration of ammonia nitrogen and nitrite. 
However, nitrifying bacteria have two flaws: they grow slowly, it is difficult to gain a competitive advantage against heterotrophs in aquaculture water with high organic matter content, and they have poor adaptability to changes in the external environment. Therefore, at present, nitrifying bacteria are not widely used in aquaculture. In recent years, studies have found a class of microorganisms that can not only purify water but also use organic matter as a carbon source—heterotrophic nitrifying bacteria. Compared with autotrophic nitrifying bacteria, heterotrophic nitrifying bacteria grow fast, can multiply rapidly in aquaculture water bodies rich in organic matter, form dominant bacteria, and can quickly and effectively reduce the concentration of ammonia nitrogen and nitrite, which is an excellent research and development candidate strain for aquaculture water quality control.
A little expert in water purification - red coccusRhodococcus ruber is one of the "ruthless characters" of the heterotrophic nitrifying bacteria mentioned above. It obtains energy and carbon sources for growth by oxidizing organic matter and utilizes inorganic or organic nitrogen as a nitrogen source. Studies have shown that red coccus can degrade pollutants that are difficult to decompose such as petroleum and terpenes, and can also effectively remove ammonia nitrogen from wastewater.
The author's research group obtained a strain of Rhodococcus erythrococcus hdrr2y (invention patent has been applied, application number 2020101595842)。It was found that the strain had good ammonia nitrogen and nitrite removal effects, and the growth rate was fast. During fermentation, the HDRR2 strain concentration increased from 104 cfu ml to 109 cfu ml within 24 h (Figure 1). During fermentation, the cell morphology of the strain changes from initially globular or short rod to long curved rod, and in the late fermentation stage, the cells become shorter and spherical again (Figure 2). After adding the strains to the culture water, the mass concentration of the strain increased from 106 cfu ml to 108 cfu ml within 48 h, and after adding the strain for 3 days, the ammonia nitrogen and nitrite concentrations in the culture water decreased significantly, and the ammonia nitrogen concentration decreased from 15 mg l on day 0 to 556 mg l with a removal rate of 6296%；The nitrite mass concentration was reduced from 15 mg l to 695 mg l with a removal rate of 5937% (Figure 3). 
Fig.1 Changes in bacterial concentration during the fermentation process of HdrR2Y strain of red coccus.
Fig.2 Morphological changes of Hdrr2Y strain of red coccus during fermentation
Fig.3 Effect of Hdrr2Y on ammonia nitrogen and nitrite in aquaculture waterThe author studied the effects of five common environmental factors, including Hdrr2Y concentration, temperature, ammonia nitrogen, nitrite concentration, rotation speed (water flow velocity) and salinity, on the removal of ammonia nitrogen and nitrite by HdrR2Y. The results showed that temperature and ammonia nitrogen concentration could significantly affect the ammonia nitrogen removal effect of HDR2Y (P<0.).05), temperature and rotational speed significantly affected the nitrite removal effect of HDR2Y (P<005)。In addition, the study also showed that the strain HDR2Y has a wide range of adaptation to the environment, and can grow in the aquaculture water with a salinity of 5 40 and a water temperature of 10 40, and its effect on removing ammonia nitrogen and nitrite is the best in the water temperature range of 25 32. In summary, Hdrr2Y is a heterotrophic nitrifying bacterium, which can grow rapidly in aquaculture water with rich organic matter content, has a wide range of salinity and temperature adaptation, can effectively reduce the concentration of ammonia nitrogen and nitrite in water, and has great application and promotion potential. Write at the end
Back to the opening question: What is water cultivation?How to raise water?
To put it bluntly, raising water is to raise the living environment of aquatic animals. If you want to raise good water, nitrifying bacteria are indispensable. In the future, if you find that the ornamental fish at home are poisoned by ammonia nitrogen and nitrite, in addition to changing the water, you can also add an appropriate amount of nitrifying bacteria to purify the water quality. It is worth mentioning that nitrifying bacteria like to attach to objects with rough surfaces to multiply, so you can put decorations such as rough stones in the fish tank. At the same time, nitrifying bacteria are a class of aerobic bacteria, and adequate oxygen is essential for the nitrogen cycle. If there is enough oxygen in the water body of the fish tank, it can help the nitrifying bacteria work and multiply faster. In addition, the most suitable temperature for nitrifying bacteria to multiply is around 25. Finally, the perfection of the entire nitrification system takes about 1 month, so there is no urgency. In the process of fish farming, our red coccus can be used regularly, which can not only decompose manure and bait, clean the water environment, but also eliminate ammonia nitrogen and nitrite to ensure the health of the fish. References.
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Related Articles:Xu Yu, Hu Xiaojuan, Zhang Song, Xu Wujie, Su Haochang, Wen Guoliang, Cao Yucheng*Effects of five factors on the removal of ammonia nitrogen and nitrite by Hdrr2Y in Hdrr2Y[J].Southern Aquatic Sciences. doi: 10.12131/20220044.
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Written by |Xu Yu.
Edit |Zhang Liping.
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