INTRODUCTION:

The word probiotic comes from a Greek origin “pro bios” which means “for life” was first coined by Lilly and Stillwell (1965)⁹. Probiotics are beneficial bacteria that maintain the health of humans and animals. Probiotics found in gastrointestinal tract of vertebrates, reduces the growth of pathogens and hence improves the intestinal microbial balance of the host¹². The use of probiotics through dietary supplements enhances innate immunity and provide resistance from pathogens⁴. Supplementation of probiotics has many health benefits such as it reduces serum cholesterol level, improves gastrointestinal function, and lowers the risk of colon cancer. Probiotics are also nutrient reserves for the host as they have the endogenous enzymes present inside the cell and exogenous enzymes secreted by the bacterial cells. These enzymes are released when the cells are lysed by acidic environment of host’s stomach.

These enzymes increase the digestibility rate of animals. Probiotic containing foods are yogurt, soya beverages, tempeh, miso and some juices. Bacteriocins produced by probiotic bacteria are used by food industry so as to reduce the use of chemical preservatives in foods with high risk for pathogen contamination. About 30-40 trillion micro-organisms in humans colonize in the intestinal tract. Major role of the gut microbiota in the host include synthesis of vitamins, digestion, carbohydrate fermentation and prevention of colonization by pathogens. Bacteria present in healthy human gut are either Gram-positive such as Lactobacillus, Ruminococcus, bifidobacterium, and Gram-negative bacteria such as Echerichia.

Most of the probiotics are lactic acid bacteria and they are isolated from animal source. Lactic acid bacteria are Gram-positive organisms which are used in medical and veterinary functions. Lactic acid bacteria prohibit the growth of various gram-positive or gram-negative bacteria, this is attributed to the secretion of lactic and acetic acid, hydrogen peroxide, bacteriocins. Recent reports propose that best sources of Lactic acid bacteria are diary fermented products such as yogurt, cheese and other fermented milk products¹¹. Major part of lactic acid bacteria are Lactobacillus spp. Lactobacillus strains are non spore-forming, usually catalase-negative, non-motile, and facultative anaerobic. Different species of Lactobacillus are: Lactobacillus rhamnosus, L. casei, L. johnsonii and L. acidophilus. These bacteria are reside in our digestive, urinary and genital systems without causing disease. Aquaculture is the rapid growing food production sector in the world but the prevalence of disease is the major threat to aquaculture production. Disease is the major threat to aquaculture production. One of the conventional solution to control the disease is the use of antibiotics, but they have adverse effect on the aquatic organisms when used in excess and over a long time. So probiotics serves as a new aid to control disease and to improve water quality in the aquaculture industry. Water quality is an important factor that affects the prevalence of fish disease. It is essential to maintain water quality to allow the production of disease free fish. Recent reports have shown that bacteria of genus Bacillus are considered as probiotics for water treatment because they have the ability to sequester matter into CO₂ ². It has been verified that bacteria of genus Bacillus decrease nitrite, nitrate and ammonium concentrations in ornamental fish water⁸.

Probiotics are also used for prevention of infectious disease in fish. Aeromonas salmonicida causes disease in fish called furunculosis and it causes huge loss to hatcheries. Probiotics have a good safety record. Side effects of probiotics if occur consists of slight digestion problem such as gas. All probiotics are not same for example if Lactobacillus prevents a disease that does not mean Bifidobacterium have the same effect.

Fig 1: Benefits generated by the Probiotics.

The primary remedial capabilities of Lactobacillus acidophilus and Bifidobacteria are:

· Improve inflammation of intestines.

· Improve irritable bowel syndrome.

· Prevention of colon cancer.

· Prevent high cholesterol level.

· Improve lactose tolerance.

· Prevent gastrointestinal tract diseases.

· Prevent diarrheal diseases.

· Stabilize the gut mucosal barrier.

Probiotics in fish farming:

Probiotics used in aquaculture are different from those terrestrial environment. Aquatic animals have a much closer interaction with the external environment. Aquatic animals take up a lot of pathogens due to breathing and feeding. Therefore, the definition of probiotics for aquatic use should be modified as the aquatic organisms share a complex relationship with their external environment. Irantio and Austin defined probiotics, for aquatic use as “an entire or components of a micro-organism that is beneficial to the health of the host”¹⁵. Probiotics enhance the growth of fishes by increasing their feed conversion efficiency and protein efficiency. The growth rate of marine larvae is increased by the use of probiotics as they yield cell products and micronutrients like essential fatty acids, vitamins, minerals or even enzymes. When added to the feed of Rohu fingerlings, probiotics provide benefits like disease resistance against pathogens, growth enhancement and immune stimulation. In addition to this, the growth of microbiota is also enhanced, harmful pathogens are inhibited and body’s natural defenses are strengthened by the use of probiotics. Probiotics have tendency to attach to the gut mucus and can block the common pathway of infection by pathogens. The growth of pathogens is also inhibited by the production of inhibitory substances which are harmful to their growth. In some cases probiotics help in the completion of larval cycle without the use of antibiotics⁶.

There has been a growing use of probiotics in fish feed and in aquaculture to enhance health benefits in fish. There is a need to manufacture probiotics which can withstand feed processing. Probiotics and their positive effects is a field of extensive research. Although clinical studies on probiotics have initiated, but this field is still being considered in its ‘infancy’. Therefore, wide range of study can be done on probiotics. Also a wide range of probiotic species can be studied viz. Lactobacillus, Bacillus, Pseudomonas etc.⁷ The mechanism of probiotic action is largely unknown. Moreover, there is a risk of transference of resistance against antibodies by probiotics to the human population through fresh water food. Extensive research can be done to either eliminate or reduce this risk. Probiotics have opened a new era of disease control in aquaculture. Probiotics provide a diverse and broad field of research which will not only help in understanding its mode of action but will also help in evaluating the future prospects of probiotics and their safe use. Aquaculture is considered as a means to meet the growing demand for fresh water food. Also, the use of probiotics has increased in recent years¹⁴. In addition to evaluating the properties of probiotics, it is equally important to study the probiotic resistance against antibodies and the risk of transmission of this resistance to other pathogens in gastrointestinal tract and in _{turn to
humans due to consumption of aquaculture products10.}

Aquaculture industry, at present, is the fastest growing food industry in the world but bacterial diseases pose a great threat to this industry. This problem can be tackled by the use of antibiotics and antimicrobial drugs but they have a risk of transference of antimicrobial resistant genes to human environment. This problem can be overcome by the use of probiotics. Probiotics have been defined by a joint FAO/WHO panel as “ live micro-organisms that when administered in adequate amounts confer a health benefit on the host”¹⁶. The isolated probiotic strain was incorporated into the diet of fishes at different concentrations. It was observed that the fishes showed an enhanced growth, specific growth rate and feed conversion efficiency as compared to control groups. These results clearly implied that Bacillus subtilis can be used as a growth enhancing agent in the culture of common carps. In a study by Gohila (2013), rohu fingerlings were fed with a diet containing probiotics. They showed a significant increase in feed conversion ratio, feed conversion efficiency and protein efficiency⁶. These results clearly indicated the importance of probiotics in aquaculture.

Bhatnagar and Lamba (2014), isolated, identified and characterized a gut bacteria, Bacillus cereus from the gut of Cirhinus mrigala. The bacterium was cultured and incorporated in the diet of Cirhinus mrigala. The results estimated a high growth rate of fish, increase in percent gain in body weight, high protein digestibility and a low feed conversion ratio as compared to control groups. The digestion of fishes was also enhanced by supplying digestive enzymes and nutrients¹⁷. It was observed that the use of probiotics increased the beneficial microbial load in fishes and decreased the pathogenic Vibrio spp. by inhibiting them. Also, the concentration of ammonium, nitrite, nitrate and phosphate ions was decreased. Ghosh (2003), isolated Bacillus circulans from the gut of Rohu fingerlings and the cultured isolated strain was used in the diet of Rohu fingerlings⁵. It was observed that experimental groups showed better growth, lower feed conversion ratio and higher protein efficiency than control groups. However, the lipid digestibility was observed to be decrease with increase in the level of Bacillus subtilis. Sahoo et al. (2015), evaluated the probiotic properties of bacteria isolated from the gut of fresh-water fishes (Labeo rohita and Catla catla). Three strains of probiotic bacteria were isolated from Labeo rohita and two from Catla catla. Biochemical tests and PCR detection revealed that probiotic strains from Labeo rohita were Enterococcus avium, Enterococcus pseudoavium and Enterococcus raffinosus and the probiotic strains from Catla catla were Lactobacillus gasseri and Lactobacillus animalis. The probiotic strains from Catla catla are acid and bile resistant and showed inhibitory activities against pathogens like Aeromonas hydrophila. These strains were vancomycin resistant. They also exhibited high cell surface properties like hydrophobicity, auto and co-aggregation. This study showed that Lactobacillus gaseri and Lactobacillus animalis are ideal probiotics which can be used in aquaculture. Gram-negative bacteria can also be used as probiotics¹⁸. In a study by Chaudary and Qazi (2007), the effect of a probiotic, Pseudomonas pseudoalcaligenes was studied on the growth performance of Rohu fingerlings. The experimental groups showed a better growth than the control groups. The experimental groups showed an increase in body weight protein efficiency ratio than the control groups¹. This clearly validates the use of probiotics in aquaculture. Dharamraj and Rajendren (2014), assessed the probiotic properties of Bacillus infantis isolated from the gut of Labeo rohita. Seven strains of bacteria were isolated and one of them exhibited a higher inhibitory effect on pathogenic bacteria. This strain exhibited acid and bile tolerance, significant hydrophobicity and antibiotic resistance³. Based on these results, it was concluded that the isolated probiotic was ideal for use in livestock production and possessed remarkable probiotic properties. Al-Faragi and Alsaphar, 2012, isolated and identified Bacillus sp. from the gut of common carp, Cyprinus carpio. The efficiency of Bacillus sp. against common fish pathogen, Aeromonas hydrophila was also evaluated¹⁹. It was observed that Bacillus sp. inhibited the pathogen after 24 hours and the antibacterial substances were produced _{at highest level in 48 hours.
Isolation of probiotics from the gut of 28 major Indian carps (Labeo rohita,
Catla catla and Cirhinus mrigala) was done and out of all strains
four strains exhibited highest antibacterial activities against Pseudomonas
flouresens, Aeromonas hydrophilla and Edwardsiella tarde5. Biochemical
tests revealed that the strain is of Bacillus subtilis, a potential
probiotic species. The mode of action which has been widely suggested is the
competition for adhesion sites. In a study, it was observed that the presence
of probiotic bacteria inhibit the adhesion of pathogens to the mucus of gut13.
Probiotics have been seen to enhance the immune system of fish. It was seen
that supplementation of probiotic Pseudomonas aeruginosa VSG-2,
prominently increases serum lysozyme and alternative complement pathway (ACP) activities,
phagocytosis and a number of macrophages. Also the levels of serum IgM were
higher in treatment groups than control groups. The fish also had prominently
higher survival rates against Aeromonas hydrophila pathogen.}

_CONCLUSION:

Probiotics are biologically helpful bacteria for the health of vertebrates. From fish gut probiotic strain can be isolated and its commercialization might be done after analyzing all parameters of probiotics. Putative probiotic can be mixed in feed and given to fish which improves not only health of fish but also improves the water quality. Based on the above observations it can be understood that in the present era of highly evolving and pathogenic microorganisms, probiotics provide an alternative and beneficial effect to the aquaculture and probiotics can be used in the prevention of infectious diseases and also for efficient agent for heavy metal removal_.

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Received on 13.07.2018 Modified on 10.09.2018

Research J. Pharm. and Tech 2018; 11(11): 5143-5146.

DOI: 10.5958/0974-360X.2018.00939.3