Probiotic Application in a Shrimp Hatchery

by Laurence Evans - Mtunzini Prawns of South Africa

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All penaeid shrimp hatcheries encounter bacterial problems that impact on production. Antibiotic treatments to control pathogenic bacterial problems yields varying results. However, most effective antibiotics are not approved for aquaculture use and some like chloramphenicol are now banned. In the early 90's some hatcheries in Taiwan and Thailand were promoting the use of  probiotics, but these ideas were not readily accepted  by the more scientific operations (Gomes, 1992). Today the concept of probiotics is reviewed by leading scientists (Verschuere et al, 2000). Verschuere et al defines aquaculture probiotics as "a live microbial adjunct which has a beneficial effect on the host by modifying the host-associated or ambient microbial community, by ensuring improved use of the feed or enhancing its nutritional value, by enhancing the host response towards disease, or by improving the quality of its ambient environment." 
Alken Murray has taken this definition a bit further, in that specific probiotic blends are designed to handle specific functions, such as ALKEN CLEAR-FLO 1005 (a dry, synergistic blend of fourteen spore-forming Bacillus strains and eight gram-negative vegetative strains of bacteria) for sludge decomposition in aquaculture ponds. Another probiotic, ALKEN CLEAR-FLO 1006, is a  blend of natural bacteria specifically designed to discourage disease proliferation in aquatic environments by enhancing immune response of cultured species while eliminating specific pollutants that foster pathogenic Vibrio spp. and other disease causing species. This formula uses six gram-positive Bacillus and ten gram-negative vegetative strains that aggressively consume a broad spectrum of pollutants, including surfactants, fats, sugars, starch, and nominal amounts of pesticides and hydrocarbons, while eliminating the formation of hydrogen sulphide.
Bacterial problems of penaeid larval stages are typically described as follows, "In zoea syndrome, larvae stop feeding at zoea 2 stage and spend like 4-5 days without moulting to the next stage.  Larvae don't eat, have no faeces, and are totally white and without lipids.  Mortalities can go up to 80-90%.  It's caused by a Vibrio spp.  Some of the prevention methods used in Ecuador are: reducing the stocking period of the hatchery to no more than 3 days, probiotics and strong asepsis (sanitisation).  Some of the treatments used (mostly with not very good results) are antibiotics, and sacrifice." (Marcillo, 2003). I have experience bacterial outbreaks where initially healthy zoea 1 are all dead within 12 hours.
With the use of antibiotics (or to a smaller degree) disinfectants to kill bacteria, some bacteria survive (either strains of the pathogen or others) because they carry genes for resistance (Moriarty, 1999). These will then grow rapidly because their competitors are removed. Over a short period of time, antibiotic resistant bacterial strains develop and flourish. Most of the bacteria found at aquaculture sites are harmless to humans and the aquaculture species (ASIARESIST Project, 2003). They comprise a significant part of normal aquatic ecological systems and are found in large numbers. There is a risk of developing antibiotic resistance in these benign or beneficial bacteria, as bacteria have the capacity to transfer genetic information between themselves. A potential human or aquaculture species pathogen could acquire the genetic information required for antibiotic resistance from the much more numerous members of the normal bacterial community. Consequently, the use of and continued research into the use of probiotics is a much more sustainable endeavour in the long-term.

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