No abstract

Southern Bluefin Tuna Mucosal Microbiome had more similar microbial communities compared to other families. The finding that mucosal microbial communities are more similar in phylogenetically related fish species exposes an opportunity to develop mackerel as a model for tuna microbiome and parasite research.

No abstract

The parasitic blood flukes Cardicola forsteri and C. orientalis are an ongoing health concern for Southern Bluefin Tuna Thunnus maccoyii (SBT) ranched in Australia. In this study we compared the effect of treatment, company, and ranching year on blood fluke infections in ranched SBT. SBT were sampled during the 2018 and 2019 ranching seasons from praziquantel (PZQ) treated pontoons and untreated pontoons managed by two companies. Severity of infection was diagnosed by several criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. PZQ treatment remains highly effective against C. forsteri infection. Prevalence and intensity of Cardicola spp. infection was lower in 2019 than 2018 for Company A in treated pontoons at week 12 and week 17 of ranching, and lower for Company A than Company B in untreated pontoons at month 5 of ranching. Results indicate re-infection may be less likely in the environment near Company A pontoons, and consistent years of treatment may have lowered the parasite load in the environment. qPCR demonstrated higher sensitivity when comparing diagnostic methods for C. forsteri in heart, and higher specificity when comparing diagnostic methods for Cardicola spp. in gills. Continuing to monitor blood fluke infections in ranched SBT can help to detect changes in drug efficacy over time and help industry to develop a best practice for treatment.

25 Aquaculture is the fastest growing primary industry worldwide. Marine finfish culture in open 26 ocean net pens, or pontoons, is one of the largest growth areas and is currently the only way to 27 rear high value fish such as bluefin tuna. Ranching involves catching wild juveniles, stocking in 28 floating net pens and fattening for four to eight months. Tuna experience several parasite-29 induced disease challenges in culture that can be mitigated by application of praziquantel 30 (PZQ) as a therapeutic. In this study, we characterized the microbiome of ranched southern 31 Bluefin Tuna, Thunnus maccoyii, across four anatomic sites (gill, skin, digesta, and anterior 32 kidney) and evaluated environmental and pathological factors that influence microbiome 33 composition, including the impact of PZQ treatment on microbiome stability. Southern bluefin 34 tuna gill, skin, and digesta microbiome communities are unique and potentially influenced by 35 husbandry practices, location of pontoon growout pens, and treatment with the antiparasitic 36 PZQ. There was no significant relationship between the fish mucosal microbiome and incidence 37 or abundance of adult blood fluke in the heart or fluke egg density in the gill. An enhanced 38 Southern Bluefin Tuna mucosal microbiome 2 This is a provisional file, not the final typeset article understanding of microbiome diversity and function in high-value farmed fish species such as 39 bluefin tuna is needed to optimize fish health and improve aquaculture yield. Comparison of 40 the bluefin tuna microbiome to other fish species, including Seriola lalandi (yellowtail kingfish), 41 a common farmed species from Australia, and Scomber japonicus (Pacific mackerel), a wild 42 caught Scombrid relative of tuna, showed the two Scombrids had more similar microbial 43 communities compared to other families. The finding that mucosal microbial communities are 44 more similar in phylogenetically related fish species exposes an opportunity to develop 45 mackerel as a model for tuna microbiome and parasite research. 46