But a team of researchers at the National Oceanic and Atmospheric Administration (NOAA) Milford Marine Labs have found that naturally-occurring bacteria isolated from the digestive glands of adult eastern oysters (Crassostrea virginica) and northern bay scallops (Argopecten irradians irradians) may 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, designated OY15, which has been shown to significantly improve larval survival in pilot-scale trials during the first two weeks of life, the most critical stage for the organism when mortality rates are among the highest.
Known to the public for their use in yogurt and other foods to improve human digestion and health, probiotic bacteria isolated from other sources can also be used to improve survival, nutrition and disease prevention in larvae grown in shellfish hatcheries.
With shellfish aquaculture being the name of the game on the Cape and The Islands, this sort of news should interest the shellfish farmer looking for alternatives to the usual antibiotics to fight bacterial disease.
Antimicrobial drugs approved for use in aquaculture in some countries, but not the US, have traditionally been used to treat bacterial diseases, but overuse of antibiotics can result in the development of resistant strains of bacterial pathogens. The use of probiotic bacteria has become increasingly popular for improved nutrition, healthy digestion and disease prevention and is used in human foods like yogurt and in pet foods.
Hatcheries produce shellfish seed to supplement natural seed, which is often limited by loss of habitat, contamination from pollution, climate change and other factors. Bacterial diseases caused mainly by pathogenic bacteria such as Vibrio are a major cause of mortality in hatchery shellfish, particularly at the very early larval stage. This can lead to significant financial losses to commercial growers and to production of farmed shellfish, which accounts for 25 percent of the total world aquaculture product.
Hatcheries produce shellfish seed to supplement natural seed, which is often limited by loss of habitat, contamination from pollution, climate change and other factors. Bacterial diseases caused mainly by pathogenic bacteria such as Vibrio are a major cause of mortality in hatchery shellfish, particularly at the very early larval stage. This can lead to significant financial losses to commercial growers and to production of farmed shellfish, which accounts for 25 percent of the total world aquaculture product.
As demand for environmentally-friendly aquaculture grows, the use of probiotics for disease prevention and improved nutrition in shellfish aquaculture is also growing. While a number of research studies have shown promise, development of probiotics that can be used in aquaculture is a multistep process requiring fundamental research and full-scale trials, Milford Lab researchers explained.
“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, in a statement. The second part of the study was to test the new probiotic candidate on the survival of oyster larvae in pilot-scale trials during their first two weeks of life.
The Milford 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 inhibit growth of the pathogen most effectively and therefore could confer a protective effect upon oyster larval survival.
Lab studies indicated that survival of two-day old oyster larvae during two-week pilot scale trials improved when supplemented with the probiotic candidate OY15 strain. Four treatments were conducted: a larval control with no bacteria, a pathogen control with larvae and pathogen B183 only, a probiotic control with larvae and probiotic candidate OY15 only, and a combination treatment comprised of larvae and both probiotic and pathogen.
