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

Symbiotic bacteria often help their hosts acquire nutrients from their diet, showing trends of co-evolution and independent acquisition by hosts from the same trophic levels. While these trends hint at important roles for biotic factors, the effects of the abiotic environment on symbiotic community composition remain comparably understudied. In this investigation, we examined the influence of abiotic and biotic factors on the gut bacterial communities of fish from different taxa, trophic levels and habitats. Phylogenetic and statistical analyses of 25 16S rRNA libraries revealed that salinity, trophic level and possibly host phylogeny shape the composition of fish gut bacteria. When analysed alongside bacterial communities from other environments, fish gut communities typically clustered with gut communities from mammals and insects. Similar consideration of individual phylotypes (vs. communities) revealed evolutionary ties between fish gut microbes and symbionts of animals, as many of the bacteria from the guts of herbivorous fish were closely related to those from mammals. Our results indicate that fish harbour more specialized gut communities than previously recognized. They also highlight a trend of convergent acquisition of similar bacterial communities by fish and mammals, raising the possibility that fish were the first to evolve symbioses resembling those found among extant gut fermenting mammals.

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Environmental and ecological factors that shape the gut bacterial communities of fish: a meta‐analysis

Indigenous bacterial flora play a critical role in the lives of their vertebrate hosts. In human and mouse models it is increasingly clear that innate and adaptive immunity develop in close consort with the commensal microbiome. Furthermore several aspects of digestion and nutrient metabolism are governed by intestinal microflora. Research on teleosts has responded relatively slowly to the revolution in microbiomics. Nonetheless, progress has been made in biotic and gnotobiotic zebrafish models, defining a core microbiome and describing its role in development. However, microbiome research in other teleost species, especially those important from an aquaculture perspective, has been relatively slow. In this review, we examine progress in teleost microbiome research to date. We discuss teleost microbiomes in health and disease, microbiome ontogeny, prospects for successful microbiome manipulation (especially in an aquaculture setting) and attempt to identify important future research themes. We predict an explosion in research in this sector in line with the increasing global demand for fish protein, and the need to find sustainable approaches to improve aquaculture yield. The reduced cost and increasing ease of next generation sequencing technologies provides the technological backing, and the next 10 years will be an exciting time for teleost microbiome research.

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Teleost microbiomes: the state of the art in their characterization, manipulation and importance in aquaculture and fisheries

Oxidative stress defines a condition in which the prooxidant–antioxidant balance in the cell is disturbed, resulting in DNA hydroxylation, protein denaturation, lipid peroxidation, and apoptosis, ultimately compromising cells’ viability Probiotics have been known for many beneficial health effects, and the consumption of probiotics alone or in food shows that strain-specific probiotics can present antioxidant activity and reduce damages caused by oxidation However, the oxidation-resistant ability of probiotics, especially the underling mechanisms, is not properly understood In this view, there is interest to figure out the antioxidant property of probiotics and summarize the mode of action of probiotic bacteria in antioxidation Therefore, in the present paper, the antioxidant mechanisms of probiotics have been reviewed in terms of their ability to improve the antioxidant system and their ability to decrease radical generation Since in recent years, oxidative stress has been associated with an altered gut microbiota, the effects of probiotics on intestinal flora composition are also elaborated

https://www.mdpi.com/2072-6643/9/5/521/pdf

Antioxidant Properties of Probiotic Bacteria.

The body of work relating to the gut microbiota of fish is dwarfed by that on humans and mammals. However, it is a field that has had historical interest and has grown significantly along with the expansion of the aquaculture industry and developments in microbiome research. Research is now moving quickly in this field. Much recent focus has been on nutritional manipulation and modification of the gut microbiota to meet the needs of fish farming, while trying to maintain host health and welfare. However, the diversity amongst fish means that baseline data from wild fish and a clear understanding of the role that specific gut microbiota play is still lacking. We review here the factors shaping marine fish gut microbiota and highlight gaps in the research.

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The Gut Microbiota of Marine Fish.

Probiotic applications of two dominant gut Bacillus strains with antagonistic activity improved the growth performance and immune responses of grouper Epinephelus coioides

Although the gut microbiota of fish has been studied extensively using traditional or molecular techniques, little information is available on the correlation between gut microbiota and growth of host fish. In the present study, the gut microbiota of two groups of juvenile grouper Epinephelus coioides, slow growing (SG) and fast growing (FG) grouper at 75 days post-hatch (DPH), were investigated by using standard isolation and characterization procedures. The results showed that 4 Vibrio specieswere isolated and comprised 12.3% of the total gut bacteria in SG grouper, whereas only two Vibrio species were isolated and comprised 3.6% of the total bacteria in FG grouper. At the same time, Bacillus pumilus, Bacillus clausii and Psychroacter sp. were only isolated and dominated in the gut of FG fish. The 3 species showed antagonistic effect on pathogenic Vibrio, this may cause the lower number and less species of Vibrio in the gut of FG grouper and suggesting fast growing fish might harbor a favorable microbiota. The number of total cultivable aerobic and facultative anaerobic bacteria was similar in the gut of two groups, 5.4×106 CFU/g and 9.0×106CFU/g in SG and FG group, respectively. Besides those most common bacteria such as Vibrio spp., Pseudomonas spp. and Acinetobacter spp., several Gram-positive and Gram-negative bacteria not normally in the gut of marine fish were also isolated from both groups of fish. The bacteria in the gut of grouper could be classified into three groups belonging to γ-proteobacteria, β-proteobacteria and Bacilli class.

	 

	Key words: Gut microbiota, fast growing grouper, slow growing grouper,Epinephelus coioides

Gut microbiota of fast and slow growing grouper Epinephelus coioides

The effect of dietary administration of Lactococcus lactis MM1 and Enterococcus faecium MM4, two strains of lactic acid bacteria isolated from the gut of juvenile grouper Epinephelus coioides, on the growth, feed utilization, digestive enzymes and immune response of juvenile E coioides was evaluated The fish were fed for 60 days with three different diets: control diet (without probiotic), diet P1 supplemented with 10 × 108 CFU g−1L lactis or diet P2 with 10 × 108 CFU g−1E faecium Although growth and feed intake decreased slightly, significant improvement of feed utilization was observed in fish fed diet P1 and diet P2 for 60 days The hepatopancreatic protease activities in the two probiotic treatments were significantly higher than that in the control The phagocytic activity, serum superoxide dismutase activity and complement component 4 (C4) and IgM levels were not significantly affected by diet P1 and diet P2 Serum complement component 3 (C3) levels in the two treatments were significantly higher than that in the control Significant increased serum lysozyme activity was observed in fish fed the diet P1, while significant decreased lysozyme activity was observed in fish fed the diet P2 compared with the fish fed the control diet There was a significant interaction effect between diet and administration date for the complement C4 The study demonstrates potential for L lactis MM1 and E faecium MM4 to improve the feed utilization and modulate the immune function in E coioides

Effect of Lactococcus lactis and Enterococcus faecium on growth performance, digestive enzymes and immune response of grouper Epinephelus coioides

A 60-day feeding trial was conducted to assess the effect of incorporating dietary Psychrobacter sp., one predominant bacterium with antagonistic activity in the gut of fast-growing grouper Epinephelus coioides, on the growth, feed utilization, digestive enzymes and immune responses of E. coioides at regular monthly intervals. The fish were fed with control diet (without probiont) or probiotic diet supplemented with 1.0 × 108 CFU g−1Psychrobacter sp. No significant improvement in weight gain (WG) and specific growth ratio (SGR) were observed in the probiotic group, but a significant improvement in feed conversion ratio (FCR) was observed in fish fed the probiotic diet for 60 days. Although not statistically significant, enhanced hepatopancreatic protease and lipase activities and intestinal amylase activity were observed in probiotic group at day 60. A slightly increase in phagocytic activity and phagocytic index was observed in fish fed probiotic diet for 60 days. Serum lysozyme activity showed no significant differences between the probiotic group and the control group during the whole experiment period, while an increasing trend of superoxide dismutase (SOD) activity in the probiotic group was observed. Serum complement component 3 (C3) level of the probiotic group was higher than that of control in the whole feeding period, while complement component 4 (C4) level of the probiotic group was significantly higher than that of the control at day 60. The results of the current study firstly demonstrated potential for Psychrobacter sp. as a novel probiont to improve feed utilization, digestive enzymes and innate immunity in E. coioides.

Effect of dietary administration of Psychrobacter sp. on the growth, feed utilization, digestive enzymes and immune responses of grouper Epinephelus coioides

Hong-Ling Yang

Papers

Probiotic applications of two dominant gut Bacillus strains with antagonistic activity improved the growth performance and immune responses of grouper Epinephelus coioides

Gut microbiota of fast and slow growing grouper Epinephelus coioides

Effect of Lactococcus lactis and Enterococcus faecium on growth performance, digestive enzymes and immune response of grouper Epinephelus coioides

Effect of dietary administration of Psychrobacter sp. on the growth, feed utilization, digestive enzymes and immune responses of grouper Epinephelus coioides

Application of autochthonous Bacillus bioencapsulated in copepod to grouper Epinephelus coioides larvae