Annual variability of infection with Cardicola forsteri and Cardicola orientalis in ranched and wild southern bluefin tuna (Thunnus maccoyii)

Neumann, L.; Bridle, Andrew R.; Leef, MJ; Nowak, Barbara F.

doi:10.1016/j.aquaculture.2017.12.042

Cited by 13 publications

(17 citation statements)

References 30 publications

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“…DNA presence corresponded with the presence of eggs in histological sections of heart and gills. C. forsteri was the most common species which is consistent with results since 2013 [9,13] but in contrast with reports from 2008 to 2012 [14] suggesting that there has been a change in the blood fluke dynamics infection, possibly caused by praziquantel treatment used by the industry since 2013 [9]. The increase in C. forsteri in gills at harvest as measured by qPCR indicates an increase in the number of eggs in the gills.…”

Section: Discussionsupporting

confidence: 86%

“…This is due to reinfection after treatment and the eggs being resistant to praziquantel treatment [ 15 ] and in contrast to qPCR results for heart where there was no significant difference between transfer and harvest for each cohort. Overall, the severity of infection was within the range reported previously from ranched SBT [ 9 , 13 ].…”

Section: Discussionsupporting

confidence: 80%

“…Samples of gills and internal organs were fixed in 10% phosphate buffered formalin and processed for histology using routine procedures. Heart and gill samples were collected to determine the severity of infection with blood flukes using adult counts in heart flushes [ 16 ] and real-time qPCR [ 13 ]. Unless processed fresh (heart flushes), the samples were stored frozen after being fixed in RNAlater.…”

Section: Methodsmentioning

confidence: 99%

“…The severity of infection with blood flukes was determined at each sampling point. Based on our previous experience [ 4 , 13 , 14 , 16 ], industry records and lack of disease signs, presence of other pathogens was not investigated. The severity of infection with blood flukes was determined in several ways, including prevalence (percentage of fish affected) and intensity (infection severity/number of infected fish) and count of adult blood flukes in heart flushes and copy number of ITS2 rDNA in heart and gill samples.…”

Section: Methodsmentioning

confidence: 99%

“…The severity of infection with blood flukes was determined in several ways, including prevalence (percentage of fish affected) and intensity (infection severity/number of infected fish) and count of adult blood flukes in heart flushes and copy number of ITS2 rDNA in heart and gill samples. The copy number was calculated for Cardicola forsteri and Cardicola orientalis using species-specific primers and quantified polymerase chain reaction (qPCR) as previously described [ 13 ].…”

Section: Methodsmentioning

confidence: 99%

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Changes in the Splenic Melanomacrophage Centre Surface Area in Southern Bluefin Tuna (Thunnus maccoyii) Are Associated with Blood Fluke Infections

Nowak

Dang

Webber³

et al. 2021

Pathogens

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Melanomacrophage centres (MMCs) are aggregates of macrophages accumulating various pigments. They have been proposed as an indicator of fish immune response. Blood flukes are common parasites in farmed fish. Two cohorts of wild Southern Bluefin Tuna (Thunnus maccoyi) were examined at transfer, before treatment against blood flukes (pre-treatment) and at harvest. MMCs were assessed in histological sections using image analysis, while Cardicola forsteri and Cardicola orientalis infection severity was determined using qPCR, count of adult flukes in heart flushes and count of eggs in gill filaments. Fish from both cohorts showed the same pattern in the changes in the surface area of MMCs. The surface area of splenic MMCs increased over the ranching duration and was positively correlated to the PCR determined copy numbers of Cardicola forsteri ITS2 rDNA in the gills of those fish. However, the infection with blood fluke was more variable, both between cohorts and individuals within the same cohort. Eggs of blood fluke were detected in renal MMCs using histology. Cardicola forsteri had a higher prevalence than Cardicola orientalis. This study contributes to our understanding of blood fluke infections in Southern Bluefin Tuna and their interactions with MMCs.

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