A physiological investigation into methods of improving the post-capture survival of both the southern rock lobster, Jasus edwardsii, and the western rock lobster, Panulirus cygnus
Creators: name: Crear, BJ
Publisher: name: University Of Tasmania
Year: 2023

description: The southern and western rock lobsters (Jasus edwardsii and Panulirus cygnus, respectively) form the basis of two of the major seafood export industries in Australia; between them earning over $500 M export dollars yearly. Although a major portion of the catch is exported as 'whole-cooked' or 'tailed' products, an increasing share of the catch is exported live. The majority of lobsters arrive at the processing sheds as live lobsters. However, a lack of basic physiological information has impeded advances in the design and management of transport and holding systems, often resulting in a deterioration of the physiological condition of some lobsters. Such physiological deterioration may result in the final product choice for the processors being limited, leading to a reduced value of the catch. The aim of this study was to develop an understanding of the physiology of lobsters, especially in relation to factors the lobsters may be subjected to during post-capture handling practices. This information could be used to redefine postcapture handling practices and holding system design and management. Standard oxygen consumption of both species increased in response to increases in temperature and body weight. Activity had the greatest effect on oxygen consumption rates, causing an approximate 3-fold increase above standard rates. The increase in oxygen consumption due to activity decreased at temperatures approaching the upper and lower extremes of each species. After a period of activity and emersion oxygen consumption remained elevated for up to 8 hours. A marked diurnal rhythm was evident, with a 48% and 87% (J. edwardsii and P. cygnus, respectively) increase in oxygen consumption at night. This was largely related to increased activity at night. Feeding resulted in a substantial (greater than 2-fold in P. cygnus) and sustained (up to 48 hours) increase in oxygen consumption. Both species were essentially oxygen regulators, able to maintain standard rates of oxygen consumption down to around 30% water oxygen saturation. Below that oxygen level the lobsters became oxygen conformers. Activity resulted in an approximate doubling of the water oxygen level at which lobsters acted as oxygen conformers. The total ammonia nitrogen (TAN) excretion rates of both species increased with increases in temperature and body weight. Activity had minor influence on the TAN excretion rate. A diurnal rhythm was evident in J. edwardsii but not in P. cygnus. Feeding had a large affect on the TAN excretion rate, with an approximate 6-fold increase occurring in each species. The excretion rates remained high for over 24 hours post-prandial. The effect of the dissolved oxygen level on recovery of P. cygnus from a period of activity/emersion was investigated. Based on the rate of recovery of various physiological parameters (oxygen consumption, haemolymph ammonia, lactate, glucose, and pH), the maintenance of water oxygen levels close to 100% saturation is recommended. Water oxygen levels less than 60% saturation slowed the rate of recovery. All lobsters recovering in water with oxygen levels less than 20% saturation died. Carrying P. cygnus out of water imposes physiological disturbances to the lobsters. The severity of the disturbances increased when the relative humidity was lower and when wind was present. Spraying water over the lobsters prevents some of the physiological consequences of emersion, such as decreases in pH and haemolymph ammonia buildup, however it does not prevent haemolymph lactate increases. Therefore, lobsters still rely on anaerobic metabolism when emersed in sprays. There was no evidence that failure of lobsters to recover from a period of emersion was caused by gill damage. A half hour period of emersion/handling at 23¬¨‚àûC caused large physiological disturbances of P. cygnus. Halving the emersion/handling time did not decrease the extent of the physiological disturbances. Slow-chilling the lobsters to 11¬¨‚àûC prior to emersion/handling, was an effective means of decreasing the physiological disturbances associated with emersion. This study has developed our understanding of the physiological responses of the southern and western rock lobsters to factors affecting them during postcapture processes, and will allow the design and management of rock lobster holding facilities to be based on a sound scientific basis. It also represents a major contribution to knowledge on respiration and nitrogen metabolism of large decapod crustaceans.