Future of probiotic application in aquaculture: prebiotics and synbiotics.

Abstract

Recent intensification in aquaculture in India has resulted in deterioration in pond environment exposing the animals to stressful conditions. Such animals are more susceptible to opportunistic pathogens especially those leading to vibriosis, resulting in severe economic loss. Extensive use of antibiotics for prevention of bacterial infections leads to the development of antibiotic resistance and export restrictions. Probiotics Administration of probiotics is widely practised both in human and veterinary medicine as an alternative to antibiotics. In recent years application of probiotics has gained importance in aquaculture, especially in intensive shrimp culture systems which are mainly export-oriented. Though only gut acting probiotics are used in human and veterinary used in human and veterinary medicine, products used in aquaculture are classified as gut acting, soil and water probiotics. Probiotics are defined as a live microbial mixture which has a beneficial effect on the host by: or microbial modifying the gut environmental community; ensuing improved use of the feed or enhancing its nutritional value; enhancing the host response towards disease; and improving the quality of its ambient environment. During initial days of probiotics application, products used to be in lower concentrations/numbers. To counteract this, farmers used to culture the probiotics to increase the concentration by fermenting for 24-48 hrs in pond site. Then it is applied in shrimp culture ponds. As the technology improved, commercial probiotics in highly concentrated form are available in the market which could be directly applied in the ponds. These products have long shelf life and method of application is also simple. Several mechanisms have been attributed to the beneficial effects of probiotics which include competitive exclusion of pathogenic bacteria, helps digestion and provide nutrients. utilise utilise organic matter, enhance immunity and improves water quality. Generally probiotic bacteria are selected based on the ability of the bacteria to inhibit shrimp specific pathogen (vibrios) and to survive pH and enzymes of host gut environment More importantly, these bacteria should be able to colonise the gut epithelium, induce beneficial effect through enhanced nutrition and immune response and lastly probiotic bacteria should be amenable for industrial production and storage. Hence, the criteria used for selection of probiotics for application in different aquaculture systems are very crucial Bacterial species commonly selected as probiotics for use in aquaculture are Lactobacillus, Carnobacterium, Vibrio, Bacillus, Pseudomonas, Aeromonas Flavobacterium, etc. Since, economically important aquatic organisms are grown in a variety of environments, an array of probiotic bacterial species are used depending upon the salinity, pH, and temperature of the pond. A recent report on the availability of spurious probiotic products in Indian market has raised many doubts on their efficacy in the minds of technicians and farmers. Common problems of such products are inclusion of inappropriate species of bacteria and at too low densities, to be effective in target pond environment. There is a need to strictly regulate the manufacture and use of these probiotics to obtain their intended prophylactic and therapeutic effect. Such regulations are strictly monitored by European Food Safety Authority (EFSA) in European Union, Food and Drug Administration (FDA) in the US and by Health Food and Nutrition Food Association in Japan. Unfortunately, there is no such regulatory body in India to specifically monitor the sale and use of substandard probiotic products. It is important for farmers to understand that probiotics are prophylactic but not therapeutic agents, hence they need continuous application throughout the culture period and the intended effect will be slow to realise