Researcher Diane Kapareiko sampling cultivated oysters. (Photo: NOAA / deq.state.va.us)
Scientists identify promising alternative to antibiotics for shellfish farms
Tuesday, January 31, 2012, 23:40 (GMT + 9)
Shellfish farmers are increasingly using probiotic bacteria instead of antibiotics and other antimicrobials for disease prevention in their crops. Probiotic bacteria can be used to improve survival, nutrition and disease prevention in larvae grown in shellfish hatcheries in an environmentally friendly way.
Researchers at the National Oceanic and Atmospheric Administration's (NOAA) Milford Laboratory in Milford, Connecticut have found that naturally-occurring bacteria isolated from the digestive glands of adult eastern oysters (Crassostrea virginica) and northern bay scallops (Argopecten irradians irradians) could be used as potential probiotic candidates in oyster larviculture.
Two related research studies published in the Journal of Shellfish Research identify a new probiotic bacterium, OY15, shown to significantly boost larval survival in pilot-scale trials during the first two weeks of life -- the most critical stage and when mortality rates are the highest.
“We are cautiously optimistic that this probiotic candidate, OY15, will offer a number of significant benefits to the shellfish industry”, said Gary Wikfors, co-author of both studies and head of the Milford Laboratory's Biotechnology Branch.
|Five-day old oyster larvae under 10x magnification. (Photo: NEFSC/NOAA)
Hatcheries produce shellfish seed to supplement natural seed, which is often limited by factors such loss of habitat, contamination from pollution and climate change. The result is significant financial losses to commercial growers and to production of farmed shellfish, which makes up 25 per cent of the total world aquaculture product.
The use of probiotics for disease prevention and improved nutrition in shellfish aquaculture is growing, but development of probiotics that can be used in aquaculture is a multistep process requiring fundamental research and full-scale trials.
“The objective of the first part of this study was to isolate and evaluate new probiotic bacteria which, when incorporated into foods used in shellfish hatcheries, might significantly improve larval survival”, said co-author Diane Kapareiko, a microbiologist at the Milford Laboratory.
Wikfords noted that the team conducted a very cautious, step-by-step study to find the best candidates under various scenarios.
"Our bench-scale challenge studies indicated that oyster larvae exposed to probiotic candidate OY15 had the highest survival rate, and that the survival of pathogen-challenged larvae was further improved by the presence of OY15 compared to the pathogen alone. It is somewhat analogous to a human building up immunity to a certain organism by being exposed to it, but without the involvement of antibodies”, he explained.
The scientists isolated 26 candidate probiotic bacteria from oysters and scallops, of which 16 had an inhibitory effect against a known shellfish-larval pathogen (B183) of the Vibrio species of bacteria. Further screening for safe use in culturing the oyster larvae and their microalgal feed indicated which probiotic candidates would be the most effective.
Positive effects of OY15 were seen on the survival of oyster larvae, on growth of phytoplankton used as larval feed and upon oyster survival during pilot-scale larviculture conditions, Kapareiko told.
By Natalia Real