Swimming activity during harvest of southern bluefin tuna (SBT) should be reduced as much as is practical. This study of the effects of husbandry and handling techniques on flesh characteristics could not demonstrate any significant changes in the flesh colour arising from the treatments applied, but it did show a clear relationship between harvest activity and body temperature in SBT on landing.
The more that SBT struggle on capture, the hotter they become. If the objective is to chill the tuna as soon as possible after harvest, then reducing the initial temperature on the tuna is a good strategy. In this study, SBT were successfully sedated to achieve “rested harvest” using a purpose-built floating enclosure and anaesthetics such as carbon dioxide and Aqui-S. Of course, just because this study couldn’t show an effect of harvest and other alternative practices on flesh colour doesn’t necessarily mean that there isn’t any effect.
Tuna showing high levels of activity on harvest are landed with physiological and biochemical symptoms consistent with stress, and it is a general axiom that stress leads to poor flesh quality in fish and terrestrial livestock. It could simply be that existing methods of flesh colour measurement cannot meet the challenge posed by sampling fish in the narrow window of opportunity before the freshly-killed carcasses leave Port Lincoln. Another approach is probably required, perhaps by collecting data from carcasses exported to Japan.