Replacing bad bugs with good bugs
Science Centres: Fisheries
Probiotics have been defined as ‘a mono- or mixed-culture of live microorganisms that, applied to animal or man, affect beneficially the host by improving the properties of the indigenous microflora’.
Basically, there are good bacteria and bad bacteria. Probiotics is the use of good bacteria to exclude or replace bad bacteria. A common form of this principle is the use of yogurt to control thrush in human beings. At NIWA we are developing probiotics for use in the aquaculture industry.
Globally, aquaculture is expanding rapidly. The FAO estimates that by 2020 half of the world’s seafood demand will be met by aquaculture. However, in aquaculture, species are often unavoidably subjected to stress brought on by culture conditions, which in turn alters the normal bacterial balance between good/non-pathogenic and bad/pathogenic bacteria. Bad bacteria may begin to dominate, creating detrimental effects in the cultured species, such as reductions in growth, performance, and survival.
Currently the shrimp (or prawn) industry accounts for 4% of the world’s cultured aquatic species and nets about US$10 billion per annum, but, like other aquaculture industries, it is beset by diseases, most of which are due to bacteria. Antibiotics have been used in an attempt to control bacteria, particularly Vibrio harveyi, but the effectiveness of antibiotics is now poor due to the development of resistance. Many farms in the Philippines have ceased production, and in Thailand shrimp production dropped due to disease problems from 250,000 t per year to 150,000 t in 1997. This highlights the need for alternative treatments such as those offered by probiotics.
Historically, disease outbreaks have been controlled by good hatchery practice and, as a last resort, antibiotics. However, there are many problems associated with the prolonged use of antibiotics, such as the creation of resistant bacterial strains potentially harmful to the cultured species and aquaculturists alike! In response to this, and the need for more responsible sustainable aquaculture, many aquaculture facilities are actively seeking alternatives for the control and treatment of diseases. The hatchery stage of production appears to be the most vulnerable to disease outbreak because, for many species, the larval stage of production is often the most susceptible to opportunistic infections.
The NIWA bioactives team within the National Centre for Fisheries & Aquaculture is developing probiotics for aquaculture. Suitable bacteria are isolated and identified, and methods are then developed to effectively deliver ‘good’ bacteria to a variety of target aquaculture animals at the appropriate life history stage.