Abstract:
The presence of bacteria in the blood is often considered a sign of disease but a number of studies have identified bacteria in the blood of apparently healthy individuals. Discovering a healthy blood microbiome would impact the way we view fish health and have major implications for disease diagnosis in aquatic organisms. Based on results of previous studies that detected bacteria in the blood and internal organs of apparently healthy fish (Arias et al. 2013, Larsen et al. unpublished data), we hypothesized we would find diverse bacterial sequences within the blood of Red Drum Sciaenops ocellatus. We extracted DNA from whole blood and sequenced the bacterial 16S rRNA with universal primers using Illumina paired-end sequencing to identify any bacteria present within the blood.
We sampled two communities of identically reared cultured Red Drum to compare blood microbiomes and immune parameters within cohorts of the same species. We tested various blood and immune parameters (hematocrit, lysozyme activity, superoxide dismutase activity (SOD), plasma protein electrophoresis profiles) to determine if the presence of bacteria resulted in an immune reaction in the fish. A total of 138 bacterial species were identified within the blood of the apparently healthy Red Drum examined. Microbiomes differed significantly between communities as indicated by analysis of similarities. Differences in microbiome structure were correlated with total protein, hematocrit, lysozyme, and plasma protein abundances (albumin, alpha1, beta1, and beta2 globulins). No difference was found between albumin:globulin ratios of the two cohorts, suggesting no inflammatory response in these fish. Our hypothesis was supported by the various bacterial DNA sequences we found and consistent immune parameter results.
