Effect of holding duration on the immune system of western rock lobster, Panulirus cygnus

Live holding of lobsters is a major part of the post-harvest process in lobster fisheries. Following capture, animals are placed in factory tanks and held for varying lengths of time for recovery from stress due to handling, air exposure, disturbance and environmental variations. The aim of the present study was to determine the pattern of response of a range of immune and physiological parameters over varying holding periods and assess their possible application as a measure of recovery from stress of post-harvest procedures and in the determination of an appropriate duration of acclimation prior to live transport. The effect of holding duration on the following immune parameters: total haemocyte counts (THC), haemolymph clotting times, haemolymph pH, haemolymph protein concentration and the differential proportion of haemocytes, was assessed. Lobsters brought to the factory were placed in holding tanks and sampled over a period of up to 10 days. Two studies were conducted, the first on lobsters from different catch groups and the second on lobsters from the same day's catch from the same area. Experiments were conducted on adult animals (10-12 animals/treatment group) with a different group of lobsters being sampled at each time point. Various immune parameters showed alterations with time during holding. A consistent observation was significantly prolonged clotting times following four days of holding. The haemolymph pH showed a strong positive correlation to clotting time and the hyaline cell proportion showed a strong negative correlation with semi-granular cells. Although the levels of THC, clotting time and differential cell counts after one day of holding were similar to those observed in other studies on rested post-harvest lobsters, suggesting that the lobsters had recovered from the acute stress of capture and transport, subsequent alterations in pH, clotting time and differential cell counts indicated other physiological adjustments were still occurring for up to 4 days post capture. Overall the results suggest that though the effects of post-harvest procedures on the immune parameters appear to be resolved after a short duration of holding at low temperatures, no single immune parameter can provide predictable indication of the acclimation process.