Biological Mechanisms
The effects of probiotics in aquaculture facilities stem from the following biological mechanisms:
- Competition for nutrients & energy sources. All microorganisms require chemical elements for growth. Aquatic pathogens require Fe (iron) for growth and proliferation. Probiotics out-compete pathogens for Fe, thus limiting pathogen growth.
- Manipulation of bacterial communities. In aquatic environments, hosts and microorganisms share the same ecosystem. By modifying the bacterial community in an aquatic medium the composition of gut microbiota is modified as well.
- Production of inhibitory compounds. Release of chemicals having a bactericidal or bacteriostatic effect - Lactobacillus spp., Pseudomonas fluorescens and Streptococcus lactis - produces bacteriostatic substances; several marine bacteria (V. alginolyticus) produce bacteriolytic enzymes against pathogenic Vibrio spp; several freshwater bacteria (Alteromonas spp.) produce bacteriolytic enzymes against Aeromonas salmonicida and A. Hydrophila spp.
- Competition for adhesion sites (intestines and gills). Adhesion to enteric mucus is necessary for many pathogenic bacteria to become established in fish intestines. Colonization with a probiotic that is well adapted to the existing intestinal environment reduces adhesion sites for pathogens.
- Enhancement of the immune response. Probiotics enhance non-specific immune response systems of animals and render them more resistant to infections by viruses, bacteria, fungi and parasites.
- Improvement of water quality. Probiotics offer a well document effect of improving water quality due to nitrifying abilities, mostly by Gram + bacteria which are good converters of organic matter back to CO2.
Technology
