Jackson Estuarine Laboratory


Microbiology of summer flounder Paralichthys dentatus fingerling production at a marine fish hatchery


The microbiology of summer flounder, Paralichthys dentatus, fingerling production was monitored over the course of 10 production cycles during 1996–1999 at a commercial marine fish hatchery. Samples of the rearing water, fish larvae and live feed were analyzed to quantify the total heterotrophic bacteria (marine agar) and total presumptive vibrios. Selected bacterial isolates were characterized to the group or species level. The tank water was compared between two larviculture methods to see if greenwater densities or the timing of fish movements could affect the tank microbiology. The extensive use of phytoplankton as rotifer enrichment and as greenwater reduced the incidence of vibrios as a percentage of total heterotrophs in the rotifers and water. Rinsed enriched Artemia had high levels of vibrios, and the fish larvae experienced increased mortality during the period of Artemia feeding although known bacterial fish pathogens were not detected at significant levels. The microbiota of the rearing water and fish intestine were similar to that of the live feed being utilized at the time of the sampling. A succession of bacterial phenotypes was observed in the rearing water and the fish intestine from day 1 to day 90 post-hatch, and the fish larvae showed evidence of the development of a stable indigenous microbiota during and after metamorphosis. Acinetobacter, Agrobacterium, Flavobacterium, Moraxella and Pseudomonas were the dominant bacterial groups in phytoplankton, rotifers and the early larval fish and tanks.

However, Artemia and older larval stages and tanks showed a shift towards the microbiota with higher levels of Vibrio and Enterobacter. Bacillus was detected in juvenile fish but not in larval stages. The results provide a database for analyzing the role of the microbiota in health and disease of summer flounder and suggest that this microbiota may be amenable to probiotic type manipulations.

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