Biotechnology and Bioinformatics (1+1)

6.4.2.The use of probiotics in aquaculture

The research on use of probiotics in aquatic animals is increasing with the demand for environment friendly aquaculture. As an alternative strategy to antibiotic use in aquatic disease management, probiotics have recently attracted extensive attention in aquaculture. However, the use of terrestrial bacterial species as probiotics for aquaculture has had limited success, as bacterial strain characteristics are dependent upon the environment in which they thrive. Therefore, isolating potential probiotic bacteria from the marine environment in which they grow optimally is a better approach.

The common organisms in probiotic products are Aspergillus oryzae, Lactobacillus acidophilus, L. bulgaricus, L. plantarium, Bifidobacterium bifidium, Streptococcus lactis and Saccharomyces cerevisiae.

Other bacteria that have been used successfully as probiotics belong to the genus Vibrio and Bacillus, and the species Thalassobacter utilis.

These products can be administered through water or incorporated in the feed. Probiotics have been particularly useful in the early stages of larval growth since the gut of the newly hatched larvae is sterile and administering probiotics through water at this stage helps to build up beneficial bacteria much faster than the normal course.

The benefits of the supplements include

• improved feed value,
• enzymatic contribution to digestion,
• inhibition of pathogenic microorganisms,
• antimutagenic and anticarcinogenic activity,
• growth promoting factors, and increase immune response.

Improved water quality has especially been associated with probiotics. It has been reported that use of Bacillus sp. improved water quality, survival and growth rates and the health status of juvenile Penaeus monodon and reduced the pathogenic vibrios. Recent research also shows that the use of commercial probiotics in Penaeus vannamei ponds can reduce concentrations of nitrogen and phosphorus and increase the shrimp yields.

The future application for probiotics in aquaculture looks bright. There is an ever-increasing demand for aquaculture products and a similar increase in the search for alternatives to antibiotics. The field of probiotics intended for aquacultured animals is now attracting considerable attention and a number of commercial products are available, particularly directed at shrimp larval culture.

Probiotics have also been used in a big way as pond cleaners in aquaculture. Probiotic bacteria directly uptake or decompose the organic matter or toxic material and improve the quality of water. The microbial cultures produce a variety of enzymes like amylase, protease, lipase, xylanase and cellulase in high concentrations than the native bacteria, which help in degrading waste. These bacteria have a wide range of tolerance for salinity, temperature, pH which usually exist in aquaculture operations.

The use of antibiotics in aquaculture is banned due to rejection of export consignments of marine products. Hence usage of probiotics is propagated to counter the effect of viral and bacterial infections in commercial aquaculture.

The pond probiotics also have a special blend of denitrifying bacteria that remove the algae’s primary source of food, nitrogen from the water. This drastic reduction in nitrogen concentration makes it difficult for the algae to bloom. The balance between phytoplankton, zooplankton and beneficial bacteria during culture period play a crucial role in the maintenance of pond health. There is yet no definitive parameter to judge the efficacy of probiotics. A quick and easy microbiological testing kit would be very useful in evaluating pond health on a daily basis. The usage of probiotics has been a subject of intense research all over the world and has been accepted as an alternative for antibiotics.