Dr. Andrea Larsen, one of Mote Marine Laboratory’s postdoctoral research fellows, studies the relationship between fish and bacteria, hoping to improve the fish-farming industry. 

PHOTOS BY GENE POLLUX.

THE PROBLEM

Seafood is one of the largest natural resource trade deficits in the United States, second only to oil. The United States is the second largest consumer of seafood, but remained only 15th in terms of farmed production in 2012, meaning the country imports more fish than it farms. But a major limitation to expanding the aquaculture industry is disease. With such a large number of fish in a small area, coupled with organic nutrients ideal for bacteria growth and a stressful environment, opportunistic pathogens attack and cause disease in the fish. While in the past they were treated with antibiotics, a rise in resistant microorganisms and public concern over ingesting antibiotic-treated fish have led to searching for a new, more effective solution.

THE SCIENCE

Mote wants to solve this problem by developing new probiotics, which are beneficial bacterial supplements, designed to counteract these pathogens by boosting immune system function, increasing digestion capabilities, potentially making them grow faster and producing compounds limiting the growth of the disease-causing pathogens. Scientists typically work to isolate a bacterium and then determine whether it is useful, but this results in a trial-and-error system. Using sequence-based methods, Larsen hopes to work backward, looking at the DNA of bacteria and only isolating varieties she knows are good. “Obviously it’s not very effective or efficient to grow each one and try each one as a probiotic, so I’m hoping that it will help streamline the process,” Larsen says.  

By collecting tissue from the fish larvae of several species—red drum, common snook and pompano—Larsen performs DNA extractions and sequencing. To determine which bacteria are doing more good than bad, she looks for patterns in the types that are present and more prominent in the surviving fish versus those that are dying. With this information, Mote will examine the relationships between the bacteria and fish, and once scientists find promising beneficial bacteria, they begin growing probiotics for use in trials.  

THE FUTURE

The goal of Larsen’s research is to find a cocktail of several different probiotics that improve fish health and lower levels of disease within the aquacultures. In particular, Larsen hopes to use bacteria native to the fish. Other research in the field uses bacteria from terrestrial animals like cows, but using bacteria naturally present in the fish would be more efficient. Finding successful probiotics would not only improve the fish-farming industry, but also have positive implications for stock enhancement practices, aquariums and even human health. “I’m hoping to find a bacterial species that can be used as a probiotic in a wide range of fish species,” Larsen says. “Something that helps to not only inhibit the growth of those opportunistic pathogens, but also might help the fish grow faster, maybe help them digest food better or uptake nutrients better.”