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OVERVIEW OF THE USE OF PROBIOTICS IN AQUACULTURE (PART I)

In Africa, a key consideration on the background of technology transfer to the aquaculture sector is that it should be done with respect to the protection of biological diversity of aquatic ecosystems and the potential impact on self-reliance and the economy of rural communities and people’s livelihoods.

The use of probiotics in aquaculture is increasing with the socio-economic demands of the sector; Thanks to the evolution of the state of knowledge of the gastro-intestinal microbiota of fish, and the activity of certain lactic probiotics is exploited to produce functional foods with preventive and therapeutic characteristics.

  1. Introduction

Aquaculture, which is now the fastest growing foodproducing sector in the world, is moving in new directions, intensifying and diversifying. With the increase in the intensification and commercialization of aquaculture production come many challenges, such as combatting diseases and epizootics, broodstock improvement and domestication, development of appropriate feedstuffs and feeding mechanisms, hatchery and grow-out technology, as well as water-quality management. Of these, disease outbreaks are one of the important problems that affect aquaculture production, suppressing both economic and social development in many countries. Moreover, the availability of feed for aquaculture is another significant challenge in the intensifying aquaculture industry, as feed accounts for up to 70% of operating costs for most aquaculture species. Feed quality and feeding methods therefore need to be thoroughly considered in order to improve growth performance and feed efficiency of the cultured animals. Several previous reports have suggested that probiotic supplementation can reduce disease outbreaks by enhancing the immune system of fish and shrimp, and can decrease culture costs by improving the growth and feed efficiency of fish. In addition, by improving animal physiology, the application of probiotics can lead to an improvement in water quality, as better feed efficiency may result in fish producing less waste. The application of probiotics in aquaculture has been widely used as a means of controlling disease, enhancing immune response, providing nutritional and enzymatic contributions to the digestion of the host, and improving water quality. Probiotics are also regarded as an environmentally friendly treatment method. The probiotics may be added to feed as live microorganisms to create a balanced indigenous microfloral community in the gastrointestinal tract. Moreover, probiotics are being considered for use as therapeutic agents and some farmers are already using them preferentially over antibiotics. The use of probiotics, which control pathogens through a variety of mechanisms, is increasingly viewed as an alternative to antibiotic treatment. This review summarizes studies on probiotics and evaluates further applications of probiotics in aquaculture.

  1. Definition of probiotic

The term probiotic has its origins in Greek words meaning “for life”. It was originally used by Lilley and Stillwell (1965) to describe one of the substances produced by protozoans that stimulates other microorganisms, and it was later used to describe animal feed supplements that benefit the host animal (Fuller, 1989). Fuller (1989) revised the definition to “a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance”. This definition highlights the essential component of probiotics as being live cells and not only “substances”. Other definitions used in aquaculture indicate that a probiotic is a live microbial food supplement that confers health benefits or disease resistance to the host (Lara-Flores and Aguirre-Guzman, 2009). The concept of aquatic probiotics is a relatively new one, and methods for evaluating the efficacy of probiotics are needed. Fuller (1989) proposed that a good probiotic has the following characteristics:

(1) effectiveness in application;

(2) nonpathogenic and non-toxic;

(3) existing as viable cells, preferably in large numbers;

(4) surviving and being actively involved in the metabolism of the gut environment and

(5) being stabilized and remaining viable during long periods of storage and under field conditions.

The difference in the intestinal flora of aquatic and terrestrial animals is a consequence of the differences in the surrounding environment. The intestinal microbiota of aquatic animals, therefore, mostly resembles the microbiota in the water environment. In aquatic animals, probiotic strains with two sources, indigenous and exogenous microbiota, have been isolated. Gram-negative facultative anaerobic bacteria, Vibrio and Pseudomonas, are the predominant indigenous microbiota of marine fish species. Other major indigenous microbiota of freshwater fish species include Aeromonas, Plesiomonas, representatives of the family Enterobacteriaceae, and obligate anaerobic bacteria of the genera Bacteroides, Fusobacterium and Eubacterium, but lactic acid bacteria are generally subdominant in fishes. However, the population dynamics of the indigenous gut microflora that colonize the gut are very complex, with many interrelationships among different microorganisms and among microorganisms and the host (Fuller, 1989). The maintenance and stability of microbial flora within aquatic animals is related to external environmental factors (Lara-Flores, 2011). This stability is not exhibited in bivalve larvae because of the short time for the transit of bacteria in bivalve larvae. Moreover, the effect of probiotic using on intestinal flora balance was defined and demonstrated only for some cases (Lara-Flores and Aguirre-Guzman, 2009). Tannock (1997) defined probiotics as “living microbial cells administered as dietary supplements with the aim of improving health”.

Source: https://www.researchgate.net/publication/274255141_Overview_of_the_use_of_probiotics_in_aquaculture.

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