BUGS & MORE BUGS:  USING PROBIOTICS AND THE FISH GUT MICROBIOME TO PRODUCE HEALTHY FISH FOR HUMAN CONSUMPTION.  

An urgent need exists in aquaculture of domestic seafood to develop microbial control strategies without jeopardizing productivity or encouraging the development of antibiotic resistance. An alternative to antimicrobials in disease control and production enhancement may be probiotics. Probiotics are viable cell preparations that have beneficial effects on the health of a host, by improving its intestinal balance via improved feed value, enzymatic contribution to digestion, inhibition of pathogenic microorganisms, antimutagenic and anticarcinogenic activities, growth-promoting factors, and an increased immune response. In contrast to terrestrial animals, gut microbiota of aquatic species are dependent on food, as well as water flowing through the intestine. The majority of gut bacteria can be transient and change as a function of feed type, or food/water quality. Over five years we have investigated the effects of different types of probiotics (single strain vs multiple strain) on the growth, metabolism and gut health in juvenile stages of the freshwater, Mozambique Tilapia (Oreochromis mossambicus) and the marine fish, Red Drum (Scienops ocellatus). For tilapia, a single strain of probiotic was used Lactobascillus rhamnosus IMC 501 in a dose response experiment; 0, 5, 10, 15, & 20 x 10¹¹CFU/g fishmeal. Results for growth showed the greatest (33.9%) increase at 10 x 10¹¹ CFU/g fishmeal compared to control over the 28-day experiment.  Results for metabolic rates (mgO₂ l^-1g^-1h^-1) showed an increase in metabolic rate with increasing probiotic concentrations. This may have been due to the changing composition of the gut microflora with time. QPCR and deep sequencing microbial techniques are being carried out to determine if growth and metabolic efficiency are governed by changes in gut microfloral complexity. Work on red drum has shown similar increases in growth rate (18%) in juveniles grown using a multi-strain probiotic (See poster by Busby & Hunt von Herbing.)