Effects of acute salinity stress on the survival and haemolymph biochemistry of juvenile tropical rock lobster, Panulirus ornatus, at different moult stages

Abstract

The tropical rock lobster, Panulirus ornatus, is emerging as an important species for onshore aquaculture development, with commercial grow out of lobsters from the juvenile to harvest phase likely to be conducted in outdoor raceways or pond culture systems in tropical regions of Australia. In these areas, climate has a large impact on the prevailing environmental conditions, including torrential rain and extended periods of heat waves, which can rapidly reduce or increase pond salinity for hours to weeks. The impacts of moulting on the salinity tolerance of P. ornatus survival and physiology are unknown. This study investigated the survival (LC50) and haemolymph biochemistry of P. ornatus juveniles when acutely exposed for 48 h to different salinities (10, 15, 20, 25, 30, 34, 40, 45, 50, 55, and 60 ppt) at three stages of the moult cycle (post-, inter- and pre-moult). Moult stage significantly impacted the survival of lobsters at low salinity (<34 ppt), which ranged from LC5048 = 12.5 ppt for post-moult lobster to LC5048 = 20.0 for pre-moult. There was no significant effect of moult stage on high salinity (>34 ppt) tolerance of lobsters which ranged from LC5048 = 50.5–54.5 ppt. Haemolymph osmolarity showed inter-moult lobsters to be weak hyper-regulators, with post- and pre-moult being hyper-osmoconfromers. Moult-stage significantly affected haemolymph oxyhaemocyanin and protein concentration, with pre-moults having the highest values and post-moult the lowest, with no impact of salinity treatments. At 50, and 55 ppt, oxyhaemocyanin was significantly elevated above total protein concentration compared to 34 ppt with no effect of the moult stage. While at 55 ppt, superoxide dismutase (SOD) activity was significantly lower compared to 25, 40, 45, and 50 ppt with no effect of moult stage. Our results suggest a salinity tolerance range between 20 and 40 ppt, beyond this, lobsters experience oxidative stress due to the breakdown of osmoregulation. This study provides an improved understanding of the survival and physiological impacts of acute salinity change on P. ornatus that is essential for optimising productivity protocols for the onshore aquaculture of the species.