Health Parameters and Blood Bacterial Assemblages of Healthy Captive Red Drum Sciaenops ocellatus: Implications for Aquaculture and Fish Health Management.

The newly-emerging tissue microbiota hypothesis suggests that bacteria found in blood and tissues play a role in host health, as these bacterial communities have been associated with various non-communicable diseases such as obesity, liver disease, and cardiovascular disease. Numerous reports identify bacteria in the blood of healthy finfish, indicating bacteremia may not always indicate disease. Current research priorities in aquaculture include the development of technologies and practices that will allow effective reduction in antibiotic use for prevention and treatment of disease. Overall, a better understanding of fish health is needed, particularly among species selected for commercial-scale production. This study investigated blood parameters of cultured Red Drum, Sciaenops ocellatus, with the tissue microbiota hypothesis in mind. Bacterial assemblages within the blood were characterized using next-generation sequencing and compared to various blood parameters including innate immune function enzymes between two fish cohorts reared in aquaculture. A total of 137 prokaryotic operational taxonomic units (OTUs) were identified from the blood of Red Drum. Microbiota diversity and structure varied greatly among individuals, with number of OTUs ranging from 4 to 58; however, predicted metagenomic function was highly similar between individuals and was dominated by metabolism of carbohydrates and amino acids and membrane transport. Communities were dominated by Proteobacteria, followed by Bacteroidetes, Firmicutes, and Actinobacteria. The most commonly identified genera included Acinetobacter, Bacillus, Corynebacterium, and Pseudomonas. Three genera previously identified as containing marine fish pathogens were detected: Corynebacterium, Pantoea, and Chryseobacterium. A subset of bacterial OTUs were positively correlated with superoxide dismutase activity and negatively correlated with lysozyme activity, indicating a relationship between blood microbiota and the innate immune system. The results of this study provide further evidence for the tissue microbiota hypothesis and demonstrate the potential for these communities to be linked to immunological parameters often used as biomarkers for fish health. This article is protected by copyright. All rights reserved.