Emerging trends of Probiotics in Aquaculture
Aquaculture is the farming of aquatic organisms by intervention in the rearing process to enhance production and private ownership of the stock being cultivated. The aquaculture as an industry has grown by leaps and bounds in past 10–15 years. While the boon was an economic welcome but the resultant side effects have been 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 earliest use of probiotics was to increase growth of hydrobionts . 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.
The term “probiotic” comes from Greek pro and bios meaning prolife The earliest recognition of the positive role played by some bacteria among farmers was when they consumed pathogen-containing milk and that “reliance on gut microbes for food made it possible to take steps to change the flora of our bodies and to replace harmful microbes by beneficial microbes .Later on use of the term to describe a microbial feed/food supplement was by defined as -organisms and substances that contribute to intestinal microbial balance.
Knowledge of probiotics has increased, currently it is known that these microorganisms have an antimicrobial effect through modifying the intestinal microbiota, secreting antibacterial substances (bacteriocins and organic acids), competing with pathogens to prevent their adhesion to the intestine, competing for nutrients necessary for pathogen survival, and producing an antitoxin effect. Probiotics are also capable of modulating the immune system, regulating allergic response of the body.
In contrast to terrestrial animals, gastrointestinal microbiota of aquatic species is particularly dependent on the external environment due to the flow of water passing through the digestive tract. Thus, the majority of bacteria are transient in the intestine, due to constant intake of water and food, together with microorganisms present in them. Although in the gastrointestinal tract (GIT) of aquatic animals have been reported potentially pathogenic bacteria such as Salmonella, Listeria, and Escherichia coli, probiotic bacteria and other microorganisms have also been identified. These include gram-positive bacteria such as Bacillus, Carnobacterium, Enterococcus, and several species of Lactobacillus; gram-negative, facultative anaerobic such as Vibrio and Pseudomonas, as well as certain fungi, yeasts, and algae.
The interest in probiotics as an environmentally friendly alternative is increasing .At present, there are several commercial preparations of probiotics that contain one or more live microorganisms, which have been introduced to improve the cultivation of aquatic organisms. Probiotics can be used as a food additive added directly to the culture tank or mixed with food.
The lactic acid-producing bacteria have been the focus of much interest. The human probiotic, Lactobacillus rhamnosus was used in rainbow trout for 51 days to reduce mortality by Aeromonas salmonicida, the causative agent of the fish disease “furunculosis” (one of the major fish diseases in many parts of world). Mortality was reduced from 52.6 to 18.9% when 109 cells g−1 were administered with feed, when probiotic dose was increased .Studies with Penaeus vannamei showed that using mixed cultures of probiotics increases survival, feed conversion, and the final production of farmed shrimp . Some commercial aquaculture products included prebiotics in their formulation, such as mannans, glucans, and yucca extract that further increase the beneficial effects of the product
Currently, commercial products are available in liquid or powder presentations, and various technologies have been developed for improvement on the case of fermentation processes, the interest has been focused on optimizing the fermentation conditions to increase the viability and functionality of probiotics, improving performance The production is carried out in batch cultures due to the difficulty of industrial scale operation of continuous systems Recently, systems have been developed for immobilization of probiotics, especially using microencapsulation. Microbial cells at high density are encapsulated in a colloidal matrix using alginate, chitosan, carboxymethylcellulose, or pectin to physically and chemically protect the microorganisms. The methods commonly used for microencapsulation of probiotics are the emulsion, extrusion, spray drying, and adhesion to starch
The need for sustainable aquaculture has promoted research into the use of probiotics on aquatic organisms. The initial interest was focused on their use as growth promoters and to improve the health of animals; however, new areas have been found, such as their effect on reproduction or stress tolerance, although this requires a more scientific development.
Probiotics have been used in aquaculture to increase the growth of cultivated species, in reality it is not known whether these products increase the appetite, or if, by their nature, improve digestibility. Rotifers are indispensable as the first live feed for larvae of most cultured aquatic species, due to their small size they are more accessible to larvae, for example, the nauplii of brine shrimp, which is a very common live feed. Lactic acid bacteria has been used to increase the growth of the rotifer Brachionus plicatilis and obtain best results with the addition of Lactococcus casei ssp. casei, Pediococcus acidilactici, and Lactobacillus lactis ssp. lactis.
The use of probiotics as growth promoters of edible fishes has been reported. Diet of Nile tilapia (Oreochromis niloticus) was amended with a probiotic Streptococcus strain, increasing significantly the content of crude protein and crude lipid in the fish, also weight has increased from 0.154 g to 6.164 g in 9 weeks of culture Due to the commercial importance of this species, the effect of supplementing diet with probiotics produced an increase of 115.3% when commercial formulation was used at a concentration of 2%
Examples of growth improvement of ornamental fishes include swordtail (Xiphophorus helleri, X. maculatus) and guppy, (Poecilia reticulate, P. sphenops), their feed was supplemented with Bacillus subtilis and Streptomyces, finding significative increases in growth and survival of Xiphophorus and Poecilia after 90 and 50 days of administration, respectively