Salinity presents economic and technical challenges in land-based recirculating systems in the U.S. warm water marine finfish aquaculture industry. In addition to influencing osmoregulation and osmotic stress of fish larvae , salinity can influence the larvae microbiome. Salinity is a primary abiotic determinant of diversity of free-living prokaryotic microorganisms within an aquaculture system since different microbial taxa thrive at different salinities. System microbiota affect colonization of fish tissues including skin, gills, and gut. Fish microbiota can also modulate host metabolic pathways and activate host-microbiota interactions in response to osmotic stress. S tudies suggest that m icrobial populations vary between freshwater and marine water fish species, and those reared in lower salinities may comprise fewer beneficial bacteria and more opportunistic pathogens. Identifying favorable and unfavorable microb es in both the fish microbiome and aquaculture system at different salinities can have implications for health management and disease suppression during development in larviculture.
Our study aims to optimize hatchery production of Florida Pompano (Trachinotus carolinus) by determining changes in the microbiomes of the fish and tank water when subjected to different salinities in larviculture . Larvae were reared at different salinities of 10, 20, or 30 ppt in triplicate and larvae samples were collected every three days until time of weaning (24 days post hatch ). Total genomic DNA (gDNA) was extracted from homogenized whole larvae samples using the Qiagen Blood and Tissue Kit. In tandem with larvae sampling events, environmental DNA (eDNA) was concentrated from 500 mL of tank system water using Smith-Root eDNA filter packs. Total eDNA was extracted from the filters using the Qiagen DNeasy PowerWater Kit. High-throughput DNA sequencing (16S metabarcoding on Illumina's HiSeq 2500 System ) was used to identify the prokaryotic taxonom y within Florida Pompano gDNA and corresponding water eDNA from each salinity treatment.
We hypothesized that the micro bial composition of Florida Pompano larvae and tank water would change between different salinities, with opportunistic pathogenic microbes such as Vibrio species being more abundant at 10 ppt. Additionally , bacterial members of the fish microbiome at important developmental milestones should be comparable to those found in the system environment. This study will help determine the lowest salinity required for successful hatchery production of Florida Pompano based on salinity tolerances specific to the fish larvae and a healthy microbiome. Our findings will also allow for the identification of targets for probiotics in near-future diet studies as well as potential early indicators of common aquaculture diseases.