Role of Beneficial microorganisms in Aquaculture

Role of Beneficial microorganisms in Aquaculture

 

 

"Probiotics" generally include bacteria, cyanobacteria, micro algae fungi, etc. Some Chinese researchers translate it into English as "Normal micro biota" or "Effective micro biota"; it includes Photosynthetic bacteria, Lactobacillus, Actinomycetes, Nitrobacteria, Denitrifying bacteria, Bifidobacterium, yeast, etc. Usually, it does not include micro algae. In English literature, probiotic bacteria are generally called the bacteria which can improve the water quality of aquaculture, and (or) inhibit the pathogens in water there by increasing production. "Probiotics", "Probiont", "Probiotic bacteria" or "Beneficial bacteria" are the terms synonymously used for probiotic bacteria.

 

Why should one use soil and water probiotics in aqua culture

Shrimp aquaculture production in much of the world is depressed by disease, particularly caused by luminous Vibrio and/or viruses. Antibiotics, which have been used in large quantities, are in many cases ineffective, or result in increases in virulence of pathogens and, furthermore, are cause for concern in promoting transfer of antibiotic resistance to human pathogens. Probiotic technology provides a solution to these problems.

 

The microbial species composition in hatchery tanks or large aquaculture ponds can be changed by adding selected bacterial species to displace deleterious normal bacteria. Virulence of luminous Vibrio species can be controlled in this manner. Abundance of luminous Vibrio strains decreased in ponds and tanks where specially selected, probiotic strains of Bacillus species were added. A farm on Negros, in the Philippines, which had been devastated by luminous Vibrio disease while using heavy doses of antibiotics in feed, achieved survival of 80-100% of shrimp in all ponds treated with probiotics.

 

Why only this solution better

The solution lies in the field of microbial ecology, not in the field of pharmacology, i.e. in developing new antibiotics or vaccines .Shrimp farmers have to learn to live with a complex community of microbes and manage them. The use of beneficial bacteria (probiotics) to displace pathogenic bacteria by competitive processes is a better remedy than administering antibiotics.

 

The microbial species composition in aquaculture ponds can be changed by adding selected species to displace deleterious common bacteria. Success depends upon defining the ecological process or processes to be changed, the types of deleterious species that are dominant and the desirable alternative species or strains of bacteria that could be added.

Competitive exclusion is one of the ecological processes that allows manipulation of the

bacterial species composition in the water, sediment and animal guts.

 

Why Chlorine is to be discarded

Chlorine is widely used in hatcheries and ponds, but its use stimulates the development of multiple antibiotic resistance genes in bacteria [8]. Some farmers in Thailand have reported that when chlorine is used in ponds to kill zooplankton before stocking shrimp, there is a rapid increase in Vibrio harveyi numbers after the chlorine is removed. This is to be expected as marine vibrios have very fast growth rates, and the chlorine treatment will lower the numbers of competitors for nutrients and kill algae, thus increasing food resources. It is likely, therefore, that the vibrios surviving after chlorine treatment are not only more resistant to antibiotics, but are also pathogenic.

 

 

Why Antibiotics and disinfectants are to be discouraged

If antibiotics or disinfectants are used to kill bacteria, some bacteria will survive, either strains of the pathogen or others, because they carry genes for resistance. These will then grow rapidly because their competitors are removed. Any virulent pathogens that re-enter the pond or hatchery tank, perhaps from within biofilms in water pipes or in the guts of animals, can then exchange genes with the resistant bacteria and survive further doses of antibiotic. Thus, antibiotic-resistant strains of pathogens evolve rapidly.

 

The transfer of resistance to human pathogens and gut bacteria is of major concern.

Such transfers probably happen easily and often, as discussed by Salyers . Resistance plasmids encoding for many antibiotic resistance genes were transferred between pathogenic and non-pathogenic Gram negative bacteria in several environments including sea water. In the presence of tetracycline concentrations that were not high enough to kill the bacteria, the rate of gene transfer between Vibrio cholerae and Aeromonas salmonicida increased 100 times.

 

Throughout Asia, shrimp farmers use antibiotics in large quantities. Warehouses supplying the industry in all the major centres sell a range of antibiotics in containers of 500 g or more in size. The antibiotics in current use include fluoroquinolones especially norfloxacin and enrofloxacin, furazolidone, oxolinic acid, oxytetracycline, trimethoprim and sulphadiazine. It is difficult to find out just how much antibiotic use there is in the industry, but it is possible to make an estimate from feed usage and production. In 1994 Thailand produced about 250,000 tonnes (a quarter of the world production) of farmed shrimps, which consumed about 500,000 - 600,000 tonnes of feed. With the disease problems, shrimp production last year was down to 150,000 tonnes. For each crop at semi-intensive to intensive scales of production, farmers use 5 - 10 g antibiotics per kg feed at least once per day at weekly intervals; some use them for more extensive periods.

 

Thus antibiotics would be used in about 10% of feed. It is possible, therefore, that the antibiotic usage in shrimp farm production in Thailand in 1994 was as much as 500 – 600 tonnes, assuming all farmers used them — and this does not include that used in hatcheries for fry production.

 

As much of this will end up producing bacteria with multiple antibiotic resistance in farm effluents that then contaminate coastal waters, the potential impact on human health is significant. This problem was discussed by Austin in 1983  with reference to fish farming, but it has become far worse with the major increase in shrimp farming that has occurred since then.

 

Why only Probiotic Bacteria is recommended?

The term “probiotic” has been defined as: “a probiotic is a mono- or mixed culture of live microorganisms that, applied to animal or man, affect beneficially the host by improving the properties of the indigenous microflora” [3]. In this discussion, the authors considered only human and land farm animals. In extending their definition to aquaculture, I suggest that it also applies to the addition of live, naturally-occurring bacteria to tanks and ponds in which the animals live, because these bacteria modify the bacterial composition of the water and sediment. The health of animals is thus improved by the removal, or decrease in population density, of pathogens and by improving water quality through the more rapid degradation of waste organic matter.

 

Unlike land animals, aquatic farmed animals are surrounded by a milieu that supports opportunistic pathogens independently of the host animal, and so the pathogens can reach high abundance around the animal. Vibrio grow attached to algae, and may reach high population densities after being ingested with the algae and then excreted with lysed algae in faecal pellets by zooplankton; they are gut bacteria in fish and shrimps as well as zooplankton [7]. In aquaculture ponds, where animal and algal population densities are very high, Vibrio numbers are also high compared to the open sea. The onset of shrimp disease due to exposure to high numbers of Vibrio, especially when pathogenicity has increased by overuse of antimicrobial compounds indicates that a defense is needed.

 

The species composition of a microbial community, such as that in a pond, will be determined partly by stochastic phenomena, that is, chance, and partly by deterministic and predictable factors that allow one species to grow and divide more rapidly than others, and thus dominate numerically. Chance favours those organisms that happen to be in the right place at the right time to respond to a sudden increase in nutrients, e.g. from the lysis of algal cells or the decomposition of feed pellets that fall around them. The farmer can manipulate the species composition by seeding large numbers of desirable strains of bacteria or algae; in other words, by giving chance a helping hand.

Competitive exclusion is one of the ecological processes that can be manipulated to modify the species composition of a soil or water body or other microbial environment.

Small changes in factors that affect growth or mortality rates will lead to changes in species dominance. We are still a long way from knowing all the factors that control growth rates of particular species. The complete species composition in natural environments is largely unknown, but enough is known to argue that it is possible to change species composition by making use of competitive exclusion principles. Thus bacteria can compete by secreting antimicrobial compounds that do not necessarily kill all their competitors, but increase mortality rates just enough to tip the balance in resource utilization.

 

 

 

 

In Feed:

The inclusion of probiotics in the animal feed regulates or enhances the microbial environment, allows the establishment of healthy gastro-intestinal microflora, reduces digestive upsets, improves feed conversion ratio and thus increases overall animal perfomance.

 

Pediococcus acidilactici

is known to prevent colonization of the small intestine by pathogens like Shigella, Salmonella, Clostridium difficile and Escherichia coli among small animals. It is a probiotic bacterium that presents positive effects on the balance and the role of the intestinal flora, it also reinforces the immune defense and improves the production performances of animals (Jin et al., 2000, Coppola and Turnes 2004, Stella 2005)

 

Bacillus subtilis, Bifidobacterium bifidum, Enterococcus diacetylactis, Enterococcis faecium, Lactobacillus acidophilus and other Lactobacillus species like L. casei , L. reuteri, L.rhamonosus, Sachromyces cerevisiae, Sachromyces boulardii, TRICHODERMA RESSEI

• Would decrease or prevent intestinal establishment of pathogenic microorganisms (Vandevoorde et al., 1991)
• Would re-colonize a “stressed” intestinal environment and return gut function to normal more quickly
• have reduced incidence of diarrhea (Beecham et al., 1977)
• reduced counts of intestinal coliform bacteria (Bruce et al., 1979).

 

In Pond Water Medium:

Probiotics play predominant role in water medium in the following arenas.

 

1. Control of BOD
2. Control of Turbidity
3. Control of Pollution at the Pond Bottom
4. Reduces pH
5. Reduces Incidence of Obnoxious gases
6. Controls Algal Blooms
7. Eliminates Pathogens
8. Removes fowl odour

 

Bad Soil parameters like soil pH, Pond Bottom pollution, Presence of Heavy Metals in the soil, Bound Nutrients like Phosphorous in the soil , Presence of Pollutants, Presence of Pathogens, Presence of obnoxious Gases like H2S, Ammonia will affect the survival and growth of the inhabitant.

 

Bad water parameters like pH, Salinity, Hardness, Suspended Solids, Dissolved Solids, Turbidity, Algal Blooms, Heavy Metals, Pesticides, Lack of Available N, P and K, Lack of Available Minerals, Lack of D O , Presence of Pollutants, Presence of Pathogens, presence of hazardous gases etc will hamper the growth and survival of the inhabitant.

 

 

Acetobacter Xylinum

• Degrades levulinic acid.

• Produces 3 keto 1,4 Steroids
• Produces Acetic Acid and Nucleotides

• Produces 5 nucleotides by cell culture on hydrocarbons.

• Production of Dienes, 7 – Cyano Steroids.
• Useful in dehydroxylation of cholic acids.
• Useful in steroid conversion.

 

Aspergillus niger

• Produces Sachharifying enzymes, glucoamylase, large amounts of maltase, and less amounts of amylase.
• Produces Beta galactesidase.

 

Aspergillus Oryzae

• Produces Amylase, Protease, Tannase.
• Does not produce aflatoxins.
• when fed to lactating ruminants, it is found to result in an average increase in milk production of about 0.45 kg (1.01 lb.) of milk per day.

 

Bacillus licheniformis

• Produces Enzymes like Keratinase which degrades waste and chitinous exo skeletons of the shrimp dead.
• Produces antibiotics like Bacitracin which suppress the growth of pathogenic microbes.

 

Bacillus megaterium

• Produces digestive enzymes which decompose excessive organic waste in the pond and helps to maintain the pond water medium clean.Very useful in inhibiting growth of Vibrio spp. 

• solubilises Phosphorous in higher pH of the medium.

 

1. Nitrobacter

Converts HNO2 into HNO3. (Nitrite into nitrate); Obligates autotrophs

 

1. Nitrosomonas

Obligates autotrophs; Solubilizes Phosphorous; Converts NH3 into HNO2.

 

 

Bacillus polymyxa

• Produces large quantities of enzymes like amylases which digest many types of carbohydrates, proteins and lipids in aquatic environment.
• Produces  Polymixin, a polypeptide antibiotic which suppress the growth of pathogens.

Polymixin possess the ability to damage cell membrane structure;

• Possesses unusual characteristic to fix nitrogen under anaerobic conditions;
• Solubilises Phosphorous and phosphates;
• Asymbiotic Nitrogen fixer;

• Helps in degrading organic waste

 

Bacillus pumilus Meyer and Gottheil

 

Bacillus subtilis

• Can remain active in excreta resulting in less odor, faster decomposition, and in reduction of solids;
• Degrades proteins (Proteolytic) and Carbon (amylolytic);
• Produces amino acids;
• Produces amylases, Urease and protease enzymes which help in decomposing excessive organic waste in the ponds.;
• Produces bacitracin, which interferes with regeneration of the monophosphate form of bactoprenol from the pyrophosphate form.
• Solubilises Phosphorous;
• Used to modify starches;

• Forms a symbiotic relationship with the hosts in the slime layers of aquatic animals.
• Grows in a wide ranges of  temperatures and pH from 5.5 to 10.
• Helps in denitrification by converting Nitrate into Oxygen and Nitrogen.

• Suppresses growth of undersirable microbes in the medium and as well over the host and inside the gut.

 

Cellulomonas cartae Stackebrandt and Kandler

Cellulomonas gelida (Kellerman et al) Bergey et al

Cellulomonas uda (Kellerman et al) Bergey et al

 

De Sulfo Vibrio desulfuricans

• Produces stable hydrogenase;
• Useful to remove iron from solutions, metal sulfide formations;
• Utilises Sulphates and releases H2S.

 

Lactic acid bacillus

• Produces enzymes like Amylases, Phytases, Proteases and Lipases and also adequate B comlex vitamins which help in in reducing the pH and in preventing pathogens .

• Proved effective in lowering LDL Cholesterol.
• Provides an excellent preventative effect against various diseases of the intestine.
• Increases production of Rotefiers.
• Limits the proliferation of pathogens in rotifiers.
• Provides a source of immunostimulant .
• Useful in the cases of non specific vaginitis / leucorrhoea
• Safe during lactation and in elderly

 

Lactobacillus acidophilus

• Able to help lessen the proliferation of hostile yeasts such as candida albicans. When the intestinal micro flora is disturbed)the lactobacilli can be adversely affected) under the influence of oral antibiotic therapy, or stress conditions, the use of supplemental acidophilus, in food or concentrated form, can reverse such negative processes. The regular use of acidophilus bacteria as a supplement or in food is a protective means against imbalance of the intestinal micro flora.
• Able to help reduce the level of cholesterol thus lessening the dangers of cardiovascular complications.
• Able to suppress undesirable micro-organisms in the intestine, by some competitive means like creation of lactic acid and other inhibitory substances.
• Aids in nutrient uptake;
• Controls effectively E Coli and Staphylococcus aureus.
• Enhance and allow digestion of milk sugar (lactose) by producing the enzyme lactase and generally aid in the digestion of nutrients.
• Fights Candida overgrowth;
• Found to alleviate intestinal disorders, principle being that the ingestion of large numbers of the lactobacilli may result in replacement of undesirable intestinal organisms by harmless and beneficial organisms,
• Helps in cases of chronic constipation and diarrhea by replacing undesirable intestinal organisms;
• Helps in the cases of food poisoning;
• produce lactic acid as a main product from carbohydrates.
• Produces extremely effective natural antibiotic substances that can inhibit 11 known disease causing bacteria;

• Produces enzymes like amylases, phytases, proteases and lipases and also adequate b complex vitamins which help in reducing the ph and in preventing pathogens .

 

Lactobacillus bulgaricus

• Produce natural antibiotic substances
• Enhances digestions of milk sugar by producing the enzyme lactase.
• Inhibits less desirable micro-organisms.

 

Lactobacillus casei

• Found to be effective in the treatment of certain intestinal conditions.

 

Lactobacillus delbrueckii

• Immune Stimulation
• Produces Lactic Acid 

 

L lactis

• Reduces the ability of pathogens to grow and cause infection;
• Especially effective against Listeria monorytogenes, which causes severe food poisoning.

 

Lactobacillus reutri

• Beneficial in treatment of watery diarrhea.
• Controls Cryptosporidium parvum infection;
• Effective in enhancing the growth and development of animal;
• effectively counteract weight losses caused by disease associated stress and competitively reduce Salmonella;
• Produce reuterin, an antimicrobial agent which inhibits growth of other intestinal pathogenic microbes such as Salmonella, Listeria, Escherichia;
• Reduces variability in body weights of the animals;
• Possess resistanceto bile salt and acid.
• Possess the capacity to break down soluble carboxymethyl cellulose, ?-glucan, or xylan. Possess high adhesion efficiency to mucin and mucus.
• Produces an autoaggregation-promoting protein.
• Produces fibrolytic enzymes.

 

 

Rhodococcus+ Rhodobacter 

• Produces L glutamic Acid
• Degrades pond bottom pollution effectively

 

Sacharomyces Boulardii

• Acts as an Immuno modulator
• Alleviates Diarrhoea (especially when Diarrhoea is caused by Clostridium difficile, Crohns Disease and Travellers Diarrhoea).
• helps to improve the DO
• Kills many germs, worms, bacteria, fungi and virus.
• Protects the Gastrointestinal Tract from Cholera.

 

 

Thiobacillus ferroxidans

• Oxidises ferrous ions, Sulphur and sulphides.
• Removes iron pyrites ;

 

Thiobacilus thioxidans

• Controls vibrio

 

Trichoderma reesei

• Produces glucose by enzymatic hydrolysation of cellulose.
• Produces Cellulase.
• Produces D glucanase.
• Produces cell wall lytic enzymes

 

 

 

CITATIONS:

Nogami and Maeda (1992) isolated a bacteria strain from a crustacean culture pond. The bacterial strain was found to improve the growth of crab (Portunus trituberculatus) larvae and repress the growth of other pathogenic bacteria, especially Vibrio spp., but would not kill or inhibit useful micro algae in sea water when it was added into the culture water. Among the bacteria population present in the culture water of the crab larvae, the numbers of Vibrio spp. and pigment bacteria decreased or even became undetectable when the bacteria was added into culture water. The production and survival rate of crab larvae were greatly increased by the addition of the probiotic bacteria into the culture water. They also suggested that the bacterium might improve the physiological state of the crab larvae by serving as a nutrient source during its growth. This bacterium may have a good effect in the crab larval culture as a biocontrolling agent in the future.

 

Austin et al (1992) reported a kind of micro algae (Tetraselmis suecica), which can inhibit pathogenic bacteria of fish. Teraselmis suecica was observed to inhibit Aeromonos hydrophila, A. salmonicida, Serrstia liquefaciens, Vibrio anguillaram, V. salmonicida and Yersnia ruckeri type I. When used as a food supplement, the algal cells inhibited laboratory-induced infection in Atlantic salmon. When used therapeutically, the algal cells and their extracts reduced mortalities caused by A. salmonicida, Ser. liquefaciens, V. anguillaram, V. salmonicida and Yersnia ruckeri type I. They suggested that there may be some bioactive compounds in the algal cells, and there appears to be a significant role for Tetraselmis in the control of fish diseases.

 

Smith and Davey (1993) reported that a fluorescent strain pseudomonad bacteria can competitively inhibit the growth of fish pathogen A. salmonicida. Their results show that the fluorescent pseudomonad is capable of inhibiting the growth of A. salmonicida in culture media and that this inhibition is probably due to competition for free iron. In a challenge test of the Atlantic salmon by A. salmonicida, a statistically significant reduction in the frequency of stress-induced infection in the group of fish bathed in the bacterium fluorescent pseudomonad compared to the control group was observed.

 

Austin et al (1995) reported a probiotic strain of Vibrio alginolyticus, which did not cause any harmful effect in salmonids. By using the cross-streaking method, the probiont was observed to inhibit the fish pathogens. When the freeze-dried culture supernatant was added to the pathogenic bacteria such as V. ordalii, V. anguillarum, A. salmonicida and Y. ruckeri, showed a rapid or steady decline in the number of culturable cells, compared to the controls. Their results indicated that application of the probiont to Atlantic salmon culture led to a reduction in mortalities when challenged with A. salmonicida and to a lesser extent V. anguillarum and V. ordalii. The observation with this probiotic Vibrio is encouraging, and it appears that there is tremendous potential for the use of such probiotics in aquaculture as part of a disease control strategy.

 

Maeda and Nagami (1989) reported some aspects of the biocontrolling method in aquaculture. In their study bacterial strains possessing vibrio static activity which improved the growth of prawn and crab larvae were observed. By applying these bacteria in aquaculture, a biological equilibrium between competing beneficial and deleterious microorganisms was produced, and results show that the population of Vibrio spp., which frequently causes large scale damage to the larval production, was decreased. Survival rate of the crustacean larvae in these experiments showed much higher than those without the addition of bacterial strains. They hope that addition of these strains of bacteria will repress the growth of Vibrio spp., fungi and other pathogenic microorganisms. Their data suggest that controlling the aquaculture ecosystem using bacteria and protozoa is quite possible and if this system is adopted, it will maintain the aquaculture environment in better condition, which will increase the production of fish and crustaceans.

 

Garriques and Arevalo (1995) reported that the use of V. alginolyticus as a probiotic agent may increase survival and growth in P. vannamei postlarvae by competitively excluding potential pathogenic bacteria, and can effectively reduce or eliminate the need for antibiotic prophylaxis in intensive larvae culture system. They believe that in nature a very small percentage of Vibrio sp. is truly pathogenic, and the addition of potentially pathogenic bacteria to aquaculture system through water, algae, and/or Artemia was recognized. In their study, the addition of the bacteria V. alginolyticus as a probiotic to mass larvae culture tanks resulted in increased survival rates and growth over the controls and the antibiotic prophylaxes.

 

Jiravanichpaisal and Chuaychuwong et al (1997) reported the use of Lactobacillus sp. as the probiotic bacteria in the giant tiger shrimp (P. monodon Fabricius). They designed to investigate an effective treatment of Lactobacillus sp. against vibriosis and white spot diseases in P. monodon. They investigated the growth of some probiotic bacteria, and their survival in the 20 ppt sea water for at least 7 days. Inhibiting activity of two Lactobacillus sp. against Vibrio sp., E. coli, Staphylococcus sp. and Bacillus subtilis was determined. Direkbusarakom and Yoshimizu et al (1997) reported Vibrio spp. which dominate in shrimp hatchery against some fish pathogens. Two isolates of Vibrio spp. which are the dominant composition of the flora in shrimp hatchery, were studied for antiviral activity against infectious haematopoietic necrosis virus (IHNV) and Oncorhynchus masou virus (OMV). Both strains of bacteria showed the antiviral activities against IHNV and OMV by reducing the number of plaque. Their results demonstrate the possibility of using the Vibrio flora against the pathogenic viruses in shrimp culture.

 

Sugita and Shibuga (1996) reported the antibacterial abilities of intestinal bacteria in freshwater cultured fish. They isolated bacteria from the intestine of 7 kinds of freshwater cultured fish, and investigated the antibacterial abilities of these bacteria to 18 fish or human common pathogenic bacteria. Their results indicated that the bacteria isolated from intestine of 7 kinds of freshwater cultured fish possess the antibacterial abilities, and the presence of the intestinal bacteria can protect the fish against the infection by pathogenic bacteria. Maeda and Liao (1992) reported on the effect of bacterial strains obtained from soil extracts on the growth of prawn larvae of P. monodon. Higher survival and molt rates of prawn larvae were observed in the experiment treated with soil extract, and the bacterial strain which promoted the growth of prawn larvae was isolated. They have assumed that if a specific bacterium is cultured and added to the prawn ecosystem to the level of 10 million cell/ml, other bacteria may hardly inhibit the same biotype because of protozoan activity which shall be one of the way to biologically control the aquaculture water biotype and ecosystem.

 

Maeda and Nogami et al (1992) have reported the utility of microbial food assemblages in culturing a crab, Portunus trituberculatus. Assemblages of microorganisms were produced by adding several nutrients, urea, glucose and potassium phosphate, to natural seawater with gentle aeration in which bacteria and yeast were prevailing. When these cultured microbes were added to sea water where crab larvae of Portunus trituberculatus were reared, bacteria numbers decreased very rapidly, followed by the decrease in flagellated protozoa and diatoms. Their results suggest that the crab larvae fed on these microorganisms successively. They found some strains of bacteria promoted larval growth, although yeasts did not support its growth. By adopting these assemblages of microorganisms a high yield was obtained for a prawn larva P. japonicus, although the success was not always consistent.

 

Douillet and Langdon (1994) have reported use of probiotics for the culture of larvae of the Pacific oyster (Crassostrea gigas Thunbeerg). They added probiotic bacteria as a food supplement to xenic larval cultures of the oyster Crassostrea gigas which consistently enhanced growth of larvae during different seasons of the year. Probiotic bacteria were added, at 0.1 million cells/ml, to cultures of algal-fed larvae, the proportion of larvae that are set to produce spat, and subsequently the number of spat increased. Manipulation of bacterial population present in bivalve larval cultures is a potentially useful strategy for the enhancement of oyster production. They suggest that the mechanisms of the action of probiotic bacteria are providing essential nutrients that are not present in the algal diets or improving the oyster's digestion by supplying digestive enzymes to the larvae or removing metabolic substances released by bivalves or algae.

 

Maeda and Liao (1994) have reported microbial processes in aquaculture environment and their importance in increasing crustacean production. They suggested that based on the photosynthesis of micro algae mainly, it was clarified that bacteria, protozoa and other microorganisms from microbial food assemblages use the organic matter produced by the algae and that these assemblages play a significant role in the aquatic food chain. The growth of the larvae and their production were markedly promoted by the probiotic bacteria. In their paper, they also described the presence of a bacterial clump, stained with a fluorescent dye, inside the digestive organ of the crab Portunus trituberculatus.

 

 

In China, the studies on probiotics in aquaculture were focused on the photosynthetic bacteria. Qiao Zhenguo et al (1992) have studied three strains of photosynthetic bacteria used in prawn (P. chinensis) diet preparation and their effect. Addition of the photosynthetic bacteria in the food or culture water was found to improve the growth of the prawn and the quality of the water. Cui Jingjin et al (1997) have reported on the application of photosynthetic bacteria in the hatchery rearing of P. chinensis. They used a mixture of several kinds of photosynthetic bacteria (Rhodomonas sp. ) as water cleaner and auxiliary food. Their results showed that the water quality of the pond treated with the bacteria was remarkably improved, the fouling on the shell of the larvae was reduced, the metamorphosis time of the larvae was 1 day or even earlier, and the production of post-larvae was more than that of the control.

 

We also found that some probiotic bacteria can produce some digestive enzymes; these enzymes may improve the digestion of shrimp larvae, thus enhancing the ability of stress resistance and health of the larvae

(Wang Xianghong et al 1997, in press).

 

References

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