The effects of pre-harvest stress and harvest method on the stress response, rigor onset, muscle pH and drip loss in barramundi (Lates calcarifer)

Barramundi (Lates calcarifer) farming is a significant sector of the Australian aquaculture industry with production technology rivalling that found in the salmonid or kingfish species. It is evident however that one area of production, the final harvest stage, still has room for improvement to maintain the optimum quality of the farmed domestic product. There is considerable literature that suggests harvest methods involving stress and excessive exercise contribute significantly to final flesh quality in fish. In this study the effect of harvest method on the final flesh quality was evaluated in barramundi. Harvest size barramundi were exposed to either a rested harvest technique (utilising the aquatic anaesthetic AQUI-S), or an alternative technique which aimed to simulate the harvest conditions commonly observed on Australian barramundi farms (involving air exposure and exercise prior to slaughter). Results show that time to full rigor onset was significantly delayed (12 h) in rested fish compared to the simulated harvest treatment (3 h). Flesh pH was also significantly higher and remained this way until 18 h post-harvest in rested fish. There was no difference in drip loss from flesh samples obtained from each of the two harvest methods over 4 days storage at 2-4 °C. Furthermore, in additional barramundi exposed to the simulated conventional harvest technique and not killed, but allowed to recover, significant elevations in plasma cortisol, glucose and lactate were observed. To our knowledge, this investigation presents the first information on the stress response and the effects of stress at harvest on flesh quality in barramundi. These preliminary results validate the use of rested harvest as an alternative method of improving barramundi quality and thereby further differentiating Australian product from foreign imports.