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

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