Inter-annual and intra-annual variability in blood variables and parasitic loads of wild Thunnus maccoyii

The health of southern bluefin tuna (SBT), Thunnus maccoyii, in the Great Australian Bight was assessed. Samples were obtained over 3 years (2010–2012) and over five individual schools in 2012. Several blood variables and parasite loads were measured and used as indicators of SBT health. The health of wild SBT varied among years and among schools sampled within the same month. Haemoglobin and the humoral immune parameters lysozyme and alternative complement activity explained the majority of the variation. Haemoglobin concentration, lysozyme activity, alternative complement activity, and lactate were lower in wild SBT sampled in 2010 than in 2011 and 2012. The extent to which the health differences in wild SBT may affect ranched SBT is currently unknown. Benchmark values were set for various blood parameters and parasite loads in wild SBT.