Probiotics and immunity: a fish perspective.

The growth of aquaculture as an industry has accelerated over the past decades; this has resulted in environmental damages and low productivity of various crops. The need for increased disease resistance, growth of aquatic organisms, and feed efficiency has brought about the use of probiotics in aquaculture practices. The first application of probiotics occurred in 1986, to test their ability to increase growth of hydrobionts (organisms that live in water). Later, probiotics were used to improve water quality and control of bacterial infections. Nowadays, there is documented evidence that probiotics can improve the digestibility of nutrients, increase tolerance to stress, and encourage reproduction. Currently, there are commercial probiotic products prepared from various bacterial species such as Bacillus sp., Lactobacillus sp., Enterococcus sp., Carnobacterium sp., and the yeast Saccharomyces cerevisiae among others, and their use is regulated by careful management recommendations. The present paper shows the current knowledge of the use of probiotics in aquaculture, its antecedents, and safety measures to be carried out and discusses the prospects for study in this field.

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Use of Probiotics in Aquaculture

Digestion of food depends on three main factors: (i) the ingested food and the extent to which the food is susceptible to the effects of digestive enzymes, (ii) the activity of the digestive enzymes and (iii) the length of time the food is exposed to the action of the digestive enzymes. Each of these factors is affected by a multitude of secondary factors. The present review highlights the experimental results on the secondary factor, enzymatic activity and possible contribution of the fish gut microbiota in nutrition. It has been suggested that fish gut microbiota might have positive effects to the digestive processes of fish, and these studies have isolated and identified the enzyme-producing microbiota. In addition to Bacillus genera, Enterobacteriaceae and Acinetobacter, Aeromonas, Flavobacterium, Photobacterium, Pseudomonas, Vibrio, Microbacterium, Micrococcus, Staphylococcus, unidentified anaerobes and yeast are also suggested to be possible contributors. However, in contrast to endothermic animals, it is difficult to conclude the exact contribution of the gastrointestinal microbiota because of the complexity and variable ecology of the digestive tract of different fish species, the presence of stomach and pyloric caeca and the relative intestinal length. The present review will critically evaluate the results to establish whether or not intestinal microbiota do contribute to fish nutrition.

Enzyme‐producing bacteria isolated from fish gut: a review

It is well known that healthy gut microbiota is essential to promote host health and well-being. The intestinal microbiota of endothermic animals as well as fish are classified as autochthonous or indigenous, when they are able to colonize the host's epithelial surface or are associated with the microvilli, or as allochthonous or transient (associated with digesta or are present in the lumen). Furthermore, the gut microbiota of aquatic animals is more fluidic than that of terrestrial vertebrates and is highly sensitive to dietary changes. In fish, it is demonstrated that [a] dietary form (live feeds or pelleted diets), [b] dietary lipid (lipid levels, lipid sources and polyunsaturated fatty acids), [c] protein sources (soybean meal, krill meal and other meal products), [d] functional glycomic ingredients (chitin and cellulose), [e] nutraceuticals (probiotics, prebiotics, synbiotics and immunostimulants), [f] antibiotics, [g] dietary iron and [h] chromic oxide affect the gut microbiota. Furthermore, some information is available on bacterial colonization of the gut enterocyte surface as a result of dietary manipulation which indicates that changes in indigenous microbial populations may have repercussion on secondary host–microbe interactions. The effect of dietary components on the gut microbiota is important to investigate, as the gastrointestinal tract has been suggested as one of the major routes of infection in fish. Possible interactions between dietary components and the protective microbiota colonizing the digestive tract are discussed.

https://biblio.ugent.be/publication/8517580/file/8525700.pdf

Effect of dietary components on the gut microbiota of aquatic animals. A never‐ending story?

Microbial manipulations to improve fish health and production – A Mediterranean perspective

Bacillus subtilis, a probiont isolated from the intestine of
Cirrhinus mrigala (Hamilton), was incorporated in fish feed
at four different concentrations (5 · 108, 5 · 107, 5 · 106
and 5 · 105 cells g)1) and fed to Poecilia reticulata (Peters),
Poecilia sphenops (Valenciennes), Xiphophorus helleri (Heckel)
and Xiphophorus maculatus (Gunther) for a period of
90 days. The growth parameters, proximate composition of
whole body, digestive enzymes and gut microbiology were
monitored at regular monthly intervals. The increments in
length and weight and the survival were significantly higher
(P < 0.05) and the values of food conversions were significantly
lower (P < 0.05) in fishes fed the probiotic feeds.
The administration of B. subtilis in diet resulted in an increase
(P > 0.05) in body ash and protein content and in
the specific activity of protease and amylase in the digestive
tract of all the fishes. The counts of total heterotrophs,
motile aeromonads, presumptive pseudomonads and total
coliforms were significantly lower (P < 0.05) in the gut of
the probiotic fed fishes. Bacillus subtilis persisted in the fish
intestine and in the feed in high numbers during the
feeding period. The high survival and low infectivity recorded
in the probiotic feed fed fishes when challenged by
immersion assay with the pathogenic Aeromonas hydrophila
demonstrate that the probiotic strain confers disease
resistance in live-bearing ornamental fishes. A probiotic
concentration of 106 to 108 cells g)1 is adequate for improved
growth performance and survival and for healthy
gut microenvironment and use of higher concentration of
the probiont did not always lead to significantly better
results.

Dietary probiotic supplementation in growth and health of live-bearing ornamental fishes

A probiotic bacterial strain, Bacillus subtilis, isolated
from the intestine of Cirrhinus mrigala (Hamilton),
was incorporated in ¢sh feed at four diierent concentrations
(5 � 108 cells g�2, 5� 107 cells g�2,
5 � 106cells g�1 and 5 � 105 cells g�1) and fed to
four species of livebearing ornamental ¢sh, Poecilia
reticulata (Peters), Poecilia sphenops (Valenciennes),
Xiphophorus helleri (Heckel) and Xiphophorus maculatus
(Gunther) for one year duration to observe the effect
of dietary probiotic supplementation on their
reproductive performance. Sixty virgin females of
each species were stocked separately in circular FRP
tanks (350 L) and fed diets with varying levels of probiotic
cells and control feed. Broodstock performance
was evaluated based on gonadosomatic index (GSI),
fecundity and fry production of female broodstock.
The results showed that supplementation of feed
with probiotics increased signi¢cantly (Po0.05) the
GSI, fecundity and fry production of spawning females
and length and weight of fry in all the four species
of ¢sh. The number of dead and deformed fry
were also signi¢cantly lower (Po0.05) in ¢sh fed
with the probiotic feeds.The use of higher concentration
of the probiont in diet did not always lead to signi¢
cantly improved reproductive performance of the
spawners. Collectively, this study showed that female
livebearers bene¢t from inclusion of probiotics in diet
during their reproductive stages.

Effect of probiotic on reproductive performance in female livebearing ornamental fish

Probiotic strains were isolated from the intestines of 28 Indian major carps (Labeo rohita, Catla catla, Cirrhinus mrigala) cultured in sewage-fed ponds. Intestinal microflora were isolated, counted, and identified, and their in vitro antibacterial properties were determined. The double layer method revealed that four strains (SG1, SG2, SG3, SG4) elicited antagonism against the pathogen Pseudomonas fluorescens. Using cross streak and parallel streak methods, SG4 maximally inhibited the fish pathogens Pseudomonas fluorescens, Aeromonas hydrophila, and Edwardsiella tarda. Therefore, SG4 was chosen for further study as a probiont. SG4 was nonpathogenic to C. mrigala fingerlings, and adhered well to stainless steel, high density polyethylene, and glass plate substrates. Biochemical tests showed that SG4 was endospore-forming, aerobic, motile, rod-shaped Bacillus subtilis. However, since in vitro experiments can only give an indication of in vivo success, future research should include large-scale in vivo experiments.

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Isolation of Putative Probionts from the Intestines of Indian Major Carps

Bacillus subtilis isolated from the intestine of Cirrhinus mrigala (Hamilton) was incorporated into the rearing water of Poecilia reticulata (Peters), Poecilia sphenops (Valenciennes), Xiphophorus helleri (Heckel) and Xiphophorus maculatus (Gunther) at four different concentrations (5 × 108 cells ml−1, 5 × 107 cells ml−1, 5 × 106 cells ml−1 and 5 × 105 cells ml−1) and its effect on fish growth performance and survival, water quality parameters and bacterial population of water were assessed. The results showed that the addition of bacterial cells in the rearing water resulted in greater survival and a faster growth rate and, hence, greater length and weight increments of the livebearers. The use of a bioaugmentor in the rearing water of the livebearing fishes resulted in significantly lower (P < 0.05) concentrations of dissolved organic matter and total ammonium nitrogen. The counts of motile aeromonads and total coliforms recorded in the water of bioaugmented tanks were also lower than that in the control tank. Bioaugmentation between 106 and 108 cells ml−1 in the rearing water is sufficient in establishing a bioaugmentor and the use of a higher concentration of bacterial cells did not always lead to significantly better results.

Chittaranjan Sahu

Papers

Dietary probiotic supplementation in growth and health of live-bearing ornamental fishes

Effect of probiotic on reproductive performance in female livebearing ornamental fish

Isolation of Putative Probionts from the Intestines of Indian Major Carps

Bioaugmentation in the growth and water quality of livebearing ornamental fishes

Bacterial load associated with culture of ornamental fishes in glass aquarium