What types of microbial strains are used in aquaculture?

Why use microbial strains?

1. Reduce pathogenic microorganisms and harmful algae; significantly enhance the immunity and disease resistance of cultured organisms, and increase the survival rate. Users report that aquatic EM bacteria can nearly double the survival rate of crab seedlings, raise the survival rate of humpback grouper from 30% to over 70%, and are a nemesis of many shrimp diseases.

2. Zooplankton and beneficial algae increase, especially bloodworms, which increase noticeably.

3. Stabilise and improve water quality: the water body is clear, not foul or rotten, with no odours such as hydrogen sulfide or ammonia, visibility remains long and stable at 25-50 cm, and the water change interval is extended by 2 times.

4. Fish and shrimp faeces, scraps and other waste do not turn into sludge but remain loose and sandy.

5. Promote growth, with a markedly higher weight gain rate. Under the same conditions, using EM bacterial liquid can bring the crop to market 10-15 days earlier, raise the average yield per mu by more than 20-35%, increase egg production by more than 20%, and prolong the spawning period.

First, photosynthetic bacteria

Photosynthetic bacteria, abbreviated PSB, were the earliest bacterial preparations used in aquaculture in China. Photosynthetic bacteria are bacteria that can use light energy to carry out photosynthesis that does not produce oxygen. Many friends see "photosynthetic" and compare it with the photosynthesis of chlorophyll. Photosynthetic bacteria do not produce oxygen. During their own reproduction, photosynthetic bacteria can use small-molecule organic matter as a carbon source and hydrogen donor, and use dissolved nitrogen in the water environment (such as ammonium, nitrate, nitrite, etc.) as a nitrogen source to synthesise organic nitrogen compounds. Therefore, they can consume small-molecule organic matter, ammonium, nitrate and nitrite in the water, playing a role in purifying water quality.

Photosynthetic bacteria break down small molecules, so activating them with brown sugar has no effect; brown sugar is a macromolecule.

Some people encounter high nitrite and find that photosynthetic bacteria are effective; this is also the principle behind it.

However, photosynthetic bacteria cannot use some macromolecular organic matter in the water environment. Macromolecular organic matter in the water body (such as proteins, fats and sugars) must first be broken down by other microorganisms (such as Bacillus subtilis, Bacillus spp., lactic acid bacteria, yeast, actinomycetes, sulfur bacteria, etc.) into small-molecule organic matter (such as amino acids, lower fatty acids, small-molecule sugars, etc.) before it can be decomposed and used by photosynthetic bacteria. Therefore, when using photosynthetic bacteria to purify water quality, they should be used together with other beneficial bacteria.

In our daily use of bacteria, it is best to use several kinds together, and the results are twice as good with half the effort.

The process by which photosynthetic bacteria improve the water body is usually completed under photosynthesis. Under normal circumstances, photosynthetic bacteria have a good improvement effect on the water quality of the surface layer of the water body (30-50 cm) where visible light or light energy visibility is relatively high, but for the deeper or deep-water layers of the water body where light energy visibility is relatively low, as well as the part of the pond bottom where light is difficult to reach, because photosynthesis is difficult or impossible to carry out, it is difficult to produce a good improvement effect.

Next, Bacillus spores

Bacillus spores are a large category of bacteria, and the one we use most in daily life is Bacillus subtilis. Bacillus belongs to the Gram-positive bacteria, is aerobic, can produce spores, and is a type of heterotrophic bacterium with a highly active digestive enzyme system, high temperature tolerance and stress resistance.

Bacillus can reduce the content of nitrate and nitrite in the water body, thereby improving water quality. During metabolism, Bacillus subtilis also produces a substance called subtilin that inhibits or kills other microorganisms, thereby improving water quality.

Bacillus consumes oxygen during growth and reproduction, and I estimate many people have encountered this problem. So pay attention to oxygen supplementation when using it.

The Bacillus in finished products is in a dormant state and needs to be activated (by adding organic matter such as brown sugar).

During reproduction, Bacillus secretes large amounts of amylase, protease and lipase, and can rapidly degrade residual feed and excrement of fish and shrimp. Under the joint action of other microorganisms in the pond, most of it is further decomposed into water and carbon dioxide, and a small part becomes material for the synthesis of new cells, thereby purifying the water body.

Some people encounter high nitrite and say that using Bacillus is also effective. That is also the case. So which is better at reducing nitrite: photosynthetic bacteria, Bacillus bacteria or nitrifying bacteria?

I suggest that prevention is needed in ordinary times, and that several bacteria be used together.

Next, nitrifying bacteria

Nitrifying bacteria are a type of chemolithoautotrophic bacteria that use ammonia or nitrite as their main energy source for survival and carbon dioxide as their main carbon source. They consist of two physiological subgroups: nitrosifying bacteria and nitrifying bacteria. Nitrosifying bacteria complete the conversion of NH4+ to NO2-, while nitrifying bacteria complete the conversion of NO2- to NO3-, thereby converting ammoniacal nitrogen and nitrite, which are toxic to aquatic animals, into nitrate, which is non-toxic to aquatic animals.

Nitrification is an oxidation process, and its efficiency is highest under conditions of sufficient dissolved oxygen.

Many people have used nitrifying bacteria and feel the effect is not as expected. Why? First, dissolved oxygen: nitrifying bacteria need sufficient dissolved oxygen; second, nitrifying bacteria reproduce very slowly. How slow? I have checked the data: nitrifying bacteria take 20 hours to reproduce one generation. So when your nitrite is high and only then do you think of nitrifying bacteria, it is basically useless. Nitrifying bacteria are best used for prevention. My friends, after clearing the pond, regularly dose nitrifying bacteria from the time the fry are small.

The problem of excessive nitrite is encountered by many people. Prevention is the main thing, especially in the middle and late stages: as feed increases and faeces increase, the water can no longer break them down, and then it breaks out. Controlling feed starts from the source, and the use of bacteria is also key.

Photosynthetic bacteria have low efficiency in converting nitrite, and Bacillus has low conversion of ammoniacal nitrogen.

Nitrifying bacteria have another characteristic: they need to attach, unlike other bacteria, so in some places biological carriers have been developed. Nitrosifying bacteria complete the conversion of NH4+ to NO2-, while nitrifying bacteria complete the conversion of NO2- to NO3-, thereby converting ammoniacal nitrogen and nitrite, which are toxic to aquatic animals, into nitrate, which is non-toxic to aquatic animals.

Excessive organic matter, low pH, low dissolved oxygen (below 2 mg/L), low temperature and so on will all suppress the concentration of nitrifying bacteria in the water body.

Next, yeast

Yeast differs from bacteria in that it has a true nucleus and belongs to the single-celled fungal microorganisms.

Prevention is fine, but for treatment you need to add a very large amount. Yeast can grow in both aerobic and anaerobic environments, that is, yeast is a facultative anaerobe. Under oxygen-deficient conditions, yeast breaks down sugar into alcohol and water. Under aerobic conditions, it breaks down sugar into carbon dioxide and water, and yeast grows faster when oxygen is present.

When added to food, yeast can adhere to the intestinal tract and stimulate the secretion of amylase and brush border membrane enzymes in fish and shrimp, thereby improving the animals' utilisation of food.

Yeast is an aerobic bacterium that prefers to grow in a slightly acidic environment and can multiply in large numbers in the digestive tract. The massive reproduction and growth of yeast make it the dominant population in competition for survival with harmful bacteria, inhibiting the growth of harmful bacteria. It is a good thing, but you have to know how to use it.

Next, Bdellovibrio

Many people, upon hearing Bdellovibrio, think it is something that kills Vibrio. Bdellovibrio is a bacterium that parasitises bacteria. It can attach to the cell wall of the host bacterium with its own attachment organ, and rapidly drill into the host cell, using the host's nutrients to grow and reproduce, finally causing the host bacterium to lyse.

Bdellovibrio is like a killer; it kills bacteria. Bdellovibrio is selective about its hosts, specifically parasitising Gram-negative bacteria such as Vibrio, Pseudomonas, Aeromonas and Edwardsiella. Harmful bacteria and harmful algae in nature can never be completely killed off; what we want is to let beneficial bacteria and beneficial algae dominate.

Next, EM

I believe many people use EM a lot. EM is the English abbreviation for Effective Microorganisms. It is made by compound culturing of more than 80 kinds of beneficial bacterial species from five major groups: photosynthetic bacteria, lactic acid bacteria, yeast, actinomycetes and filamentous bacteria.

That is the theory, but it is estimated that in practice the formulas of different manufacturers differ.

After EM bacteria penetrate into the water body, they can inhibit pathogenic microorganisms and harmful substances, promote the massive reproduction of plankton and increase the dissolved oxygen content in the water, maintain the ecological balance of the aquaculture water body, purify the excrement and residual feed in the aquaculture pond, and improve water quality and bottom quality, thereby reducing disease.

Next, lactic acid bacteria

If you do not mind the trouble, regularly mixing lactic acid bacteria into feed will surely have remarkable effects: forming a protective layer in the intestinal tract, blocking the invasion of pathogenic bacteria and viruses, stimulating the intestinal tract to secrete antibodies, improving intestinal immunity, promoting gastric juice secretion, and enhancing digestive function.

Microbial water quality regulators mixed with antibiotics and disinfectants: while using microbial water quality regulators to improve water quality, farmers, out of fear of diseases in cultured animals, are accustomed to using antibiotics for prevention, adding one or more antibiotics to the water body and feed over the long term in the hope of killing pathogens and reducing disease outbreaks, thinking that this two-pronged approach will ensure nothing goes wrong. Little do they know that while antibiotics kill pathogenic bacteria, they also destroy the microbial preparations composed of live bacteria.