Life on the edge: physiological problems in penaeid prawns Litopenaeus stylirostris, living on the low side of their thermopreferendum

The underlying physiological mechanisms explaining why the adult penaeid prawn Litopenaeus stylirostris cannot successfully face heavy stressful events on the low edge of its thermopreferendum (20–22°C) were studied during the austral winter. Prawns were studied during recovery from net fishing and rapid transfer from outdoor earthen ponds into indoor facilities. This was assimilated to a predator–prey interaction. O 2 -consumption, hemolymph osmotic pressure (OP h ), arterial O 2 partial pressure (PO 2 ), a–v O 2 -capacitance and mortality rates were analysed. Data were compared to similar challenges performed at 28°C during the austral summer. At 20–22°C, mortality of up to 70% was observed after 2 days whereas at 28°C, maximum mortality was 3–5%. Mortality occurred when OP h shifted towards equilibrium with seawater, the resting O 2 -consumption, the a–v O 2 -capacitance and the arterial PO 2 went down to minimal values. These events can be counterbalanced by transiently hyper-oxygenating the hemolymph or by blocking the OP h shift in isosmotic water (Wabete et al. in Aquaculture 260:181–193, 2006 ): both led to a dramatic decrease in mortality. It is concluded that in penaeid prawns L. stylirostris , a mismatch between O 2 -demand and O 2 -supply contributes to setting the geographical limits for this animal species through an impairment of their hemolymph O 2 -carrying capacity during heavy stressful events like chasing by predators.