Degree of importance of the properties that a probiotic candidate must have.
One of the problems of the aquaculture industry is the presence of pathogenic microorganisms whose proliferation is enhanced when the healthy quality of the culture systems do not meet comply with physical-chemical-biological parameters. In order to improve these problems, less aggressive alternatives to the environment have been sought. This is why probiotic bacteria are proposed as an alternative to the same systems where they will be applied, since they generate greater interest in not presenting a threat to the ecosystem, favor survival, improve the immune system of organisms and have antibacterial properties against pathogenic bacteria. This chapter reviews current research related to the search for marine probiotics for application in the aquaculture industry. Additionally, we deliver results from our work related to the research and application of probiotics. The reported studies demonstrate the positive effects of marine bacteria for their aquaculture application. The evidences found in our work allow us to conclude that larval survival is favored by the application of probiotics in the use of vectors such as rotifers, artemia and biofilms. However, depending on the species of interest, it is necessary to study the market for the biotechnological application of probiotics, to evaluate the feasibility of its production on a larger scale and its commercial feasibility.
- Seriola lalandi
In recent years, the use of antibiotics in aquaculture has been reduced due to the diverse environmental problems that it generates in the ecosystems, as for example, the selection of bacterial strains resistant to antibiotics. The incorporation of antibiotics to the culture species, besides eliminating the pathogenic microbiota, also eliminates bacteria that are beneficial for the same organism. Consequently, the accumulation of these chemicals in the organisms is not safe for human being who is the final consumer. The tendency today is to consume 100% natural foods, in search of a healthier and longer life. Likewise, the care of the environment over time has been regulated in different areas, privileging initiatives that have an environmental vision as a way to promote the care of the planet. In this area, the application of probiotics in fish culture mainly of commercial interest has been investigated for several decades. In this chapter, a bibliographical review of the recent probiotic studies in fish culture and the main results obtained from work on the use of probiotics in
2. Updated definition of probiotics in aquaculture
The word probiotic was first introduced by  to describe “substances secreted by one microorganism that stimulate the growth of another.” The name probiotic comes from the Greek “pro bios,” which means “for life” . Arora & Baldi  indicate that to date, there is no legal definition for the term probiotic. However, these authors define it as viable microorganisms with beneficial effect on the host. Akhter et al. indicate that probiotics are microorganisms that are administered orally in a sufficient amount to alter the microbiota (by implantation or colonization) of the specific host and lead to benefits for the host’s health . On the other hand, Banerjee et al. define probiotics as living microorganisms that confer beneficial effects to the host (improves immunity, helps digestion, protects against pathogens, improves water quality, and promotes growth and reproduction), and can be used as an alternative to antibiotics  (Figure 1). Probiotics include Gram-positive, Gram-negative bacteria, and many other organisms such as yeasts, bacteriophage, and single-celled algae . In the field of aquaculture, the concept of probiotic should be defined taking into account other influencing factors that differentiate it from terrestrial probiotics. For example, Verschuere et al. extend this definition as “a living microbial complement that has a beneficial effect in the host by modifying the microbial community associated with the host or environment, ensuring a better utilization of the feed or improving the nutritional value, improving the host's response against a disease, or by improving the quality of its environment” .
Das et al. suggest that probiotics are a new tool in disease control and improved water quality in the aquaculture industry. Currently, probiotics have become fashionable in the worldwide market as a dietary supplement . The interest in its consumption is related to be within the category of functional/natural foods. Rapid consumer awareness is due to the currently proven therapeutic benefits of probiotics. The benefits associated with probiotics are related to nutrient contribution, to promote survival, to improve the host immune system , and to promote growth and/or antibacterial properties against pathogenic bacteria . In addition, probiotics isolated from the same systems where they will be applied, generate greater interest by not presenting a threat to the surrounding ecosystem.
The aquaculture industry is one of the fastest growing food producing sectors in the world, as well as of significant economic importance, expectations of development estimate that much of the food of marine origin and of sweet water in the future will be provided by aquaculture. However, closed crops have threatened industry because of the proliferation of pathogens that until recently were controlled with the addition of antibiotics. The development of bacteria resistant to antibiotics means an enormous risk of transmission from the environment to the human (Pandiyan et al 2013). The development of bacteria resistant to antibiotics means an enormous risk of transmission from the environment to the human . In addition, the use of antibiotics does not discriminate and equally eliminates the beneficial microbiota in the gastrointestinal system of the organisms of interest, as well as, it accumulates in organisms affecting to man as a final consumer . Because of these problems, a global trend has been created that has led to the search for healthy alternatives with the environment to control the pathogens that cause diseases of commercial interest.
The definition of probiotics has evolved over the years, integrating new terms that are related to the new investigations regarding its application in situ. However, the magnitude of the benefit of probiotics will depend on: the concentration of the probiotic; the use of one or a mixture of probiotics of different species; the species and sanitary quality of the host; the stage of development of the host receiving the probiotic supplement (larva, juvenile and/or adult); and the physical-chemical-biological conditions of the environment. Finally, there are many interactions involved that also define the success or failure of probiotic application in culture systems. For this reason, it is fundamental to standardize the protocols, independent for each host species to be treated, since, the success of a probiotic in a specific host, does not guarantee the same beneficial result in another species of host.
3. Influence of diet and water quality on the health fish
Water quality is one of the criteria associated with outbreaks of fish diseases in crops. Therefore, it is essential to maintain water quality parameters that allow the production of disease-free fish . Improving water quality, avoiding the accumulation of organic, nitrogen, ammonia, and nitrite waste are constant concerns in aquaculture crops. High concentrations of these compounds can be extremely damaging and cause massive mortalities . In nature, these toxic substances are transformed into safer forms by the oxidizing bacteria of ammonia (ammonia to nitrite) and oxidizing bacteria of nitrites (nitrite to nitrate) .
It has been argued that probiotic bacteria can be used as ecological biocontrol or bioremediation agent for the sustainable development of aquaculture [13, 14, 15]. Among the benefits attributed to probiotics are: decreased algae growth, decreased organic load, increased nutrient concentration, increased beneficial bacterial population, inhibition of potential pathogens, and increased concentration of dissolved oxygen . Studies have shown that bacteria of the genus
The application of probiotics for fish culture requires rigorous measures that determine its effectiveness. One of them is related to the abiotic (physical-chemical) or biotic (biological) factors that will stimulate the proliferation and dominance of the probiotic only if the conditions of its surroundings are favorable for this one. The application of probiotic can be done directly to the culture water or mixed with the inoculum of “green water,” which is the entrance of microalgae in high concentrations, commonly used in fish culture for food consumption in the initial phase of the larval culture (2 days after hatching). Another pathway of probiotic entry in same fish culture is through live feed that fish receive as rotifers (up to approximately day 19 after hatching) (Figure 2), and then the addition of
4. Considerations for the selection of probiotics in aquaculture
According to Dawood et al. , a probiotic microorganism can meet the needs to develop successful aquaculture because it increases the key factors of yield in growth and disease resistance. Microorganisms intended to be used as probiotics in aquaculture should perform functions that should be considered safe not only for aquatic hosts but also for their environments and humans . According to FAO , the probiotic effect on food can have the desired impact only if it contains at least 106–107 live probiotic bacteria per gram or milliliter.
Marine microorganisms have been recognized as potential sources of relatively more stable enzymes than homologous enzymes in terrestrial microorganisms; among them, the salinity, pressure, temperature, and lighting conditions differ. Marine microbial enzymes may enhance host digestion or molecular signals involved in the quorum perception in pathogens for aquaculture disease control .
It is essential that the strain selected as probiotic does not pose a risk to the host because of the secretion of antibacterial toxins. The preselection measures are very important and should be taken to evaluate their safety before being categorized as probiotic. In this regard, there are countries that have developed standards for the application of food additives with microorganisms . Some of these norms are related to favoring potential probiotic bacteria isolated from the organism of interest to treat, mainly of the digestive system, since they have a greater capacity of adhesion to gastrointestinal mucus and tissues, compared to the foreign bacteria that are usually transient  as well as resistant to low pH.
The mechanism of action of each probiotic in specific is difficult to elucidate, because there are a variety of factors that interact between the probiotic and the surrounding environment. However, Table 1 highlights essential properties to qualify as a probiotic candidate.
5. Application of probiotics in aquaculture of fish
There is currently a variety of research focused on the probiotic search for fish culture. Table 2 below provides information based on a review of the last 5 years of research on the use of probiotics in fish aquaculture.
|Enhances the immune|||
|Modulates the digestive microbiota, an increase in growth|||
|Anguilla japonica||Increased in weight, efficiency in food and protein|||
|Asian seabass||Improved either the growth performance or disease resistance of Asian seabass against |||
|Increased larval survival|||
|Increased larval survival|||
|Decreases mortality and improves growth|||
|Increased the value of biochemical components|||
|Growth performance and feed efficiency increased|||
|Decreased susceptibility to disease|||
|Juvenile rainbow trout||Resistance against |||
|Produces extracellular enzymes that may have a role in the host digestive processes|||
|Protective effect against Vibriosis caused by |||
|Tilapia||Enhanced the growth performance and modulated some hematological parameters.|||
|Catfish||Increased the activity of digestive enzymes and the growth of catfish|||
|Growth-promoting agent and Increases growth|||
|Increases larval survival|||
|Increased the performance of zootechnical parameters|||
|Capability of improving growth performance and enhancing disease resistance by inmunomodulation|||
|Fish||Inhibitory activity against fish pathogens|||
|Fish||Inhibitory activity against the pathogen |||
|Improvement protection against pathogen outbreaks and|||
|Improves immune response and stress|||
|Antimicrobial activity against the turbot pathogens |||
|Resistance to |||
|Favoring growth, stimulation of the immune system and protection of diseases|||
From this literature review, we can highlight the novel investigations carried out in
6. Preliminary results of the probiotic search and application in
In this section, we will introduce the results of research carried out in our laboratory regarding the use of probiotics in
6.1. Isolation of the probiotic
6.2. Increased survival of
S. lalandiusing Pseudoalteromonassp. (SLP1-MESO) as probiotic
In order to evaluate the effect of the probiotic potential of
6.3. Cultivation of
S. lalandilarvae supplemented with probiotics in a mesocosmos system
In order to verify the probiotic effectiveness of
6.4. Use of biofilm as transfer vector of the probiotic
The use of fixed biofilms meshes (Nylon Sefar Switzerland, 450 μm) was evaluated as a vector to incorporate specific microalga-probiotic food and as a biological control for the benefit of
Finally, the analysis of the results obtained in these four research works would indicate that the bacterium
7. Conclusion and future perspectives
The marine microbial world does not stop surprising us, for its varied potential beneficial to animal health. Based on the literature cited in this chapter, it is evident that the probiotic search for fish application is wide. However, research must be strengthening with new biotechnological processes that allow the mass production and application of probiotics on an industrial scale at an attractive cost. In order to advance in this area and transfer the results of the research from laboratory to the industry, we must overcome some non-minor gaps, such as the legal permit that involves working with living organisms for human consumption. Despite this, it is comforting the increase in worldwide support of respect to the use of probiotics, is becoming a trend in the search for natural solutions to care the environment and to take advantage of what nature offers us.
The authors of this chapter continue to concentrate their research on the application of probiotics in the larval phase of organisms of commercial importance such as fish, molluscs, and currently echinoderms. We have the complete conviction that our specific marine wealth, located in front of the most arid desert in the world, will provide us with the solution to optimize aquaculture in phase larval stages, which will allow to increase the sustainability of aquaculture activity in Chile and South America.
The authors are grateful to the projects D10I1050 and D10E1050 of Fondef—CONICYT for supporting our research.