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

摘要

The southern and western rock lobsters (Jasus edwardsii and Panulirusudcygnus, respectively) form the basis of two of the major seafood export industriesudin Australia; between them earning over $500 M export dollars yearly. Although audmajor portion of the catch is exported as 'whole-cooked' or 'tailed' products, anudincreasing share of the catch is exported live. The majority of lobsters arrive at theudprocessing sheds as live lobsters. However, a lack of basic physiologicaludinformation has impeded advances in the design and management of transport andudholding systems, often resulting in a deterioration of the physiological conditionudof some lobsters. Such physiological deterioration may result in the final productudchoice for the processors being limited, leading to a reduced value of the catch.udThe aim of this study was to develop an understanding of the physiology ofudlobsters, especially in relation to factors the lobsters may be subjected to duringudpost-capture handling practices. This information could be used to redefine postcaptureudhandling practices and holding system design and management.udStandard oxygen consumption of both species increased in response toudincreases in temperature and body weight. Activity had the greatest effect onudoxygen consumption rates, causing an approximate 3-fold increase above standardudrates. The increase in oxygen consumption due to activity decreased atudtemperatures approaching the upper and lower extremes of each species. After audperiod of activity and emersion oxygen consumption remained elevated for up to 8udhours. A marked diurnal rhythm was evident, with a 48% and 87% (J. edwardsiiudand P. cygnus, respectively) increase in oxygen consumption at night. This wasudlargely related to increased activity at night. Feeding resulted in a substantialud(greater than 2-fold in P. cygnus) and sustained (up to 48 hours) increase inudoxygen consumption. Both species were essentially oxygen regulators, able toudmaintain standard rates of oxygen consumption down to around 30% waterudoxygen saturation. Below that oxygen level the lobsters became oxygenudconformers. Activity resulted in an approximate doubling of the water oxygenudlevel at which lobsters acted as oxygen conformers. udThe total ammonia nitrogen (TAN) excretion rates of both speciesudincreased with increases in temperature and body weight. Activity had minor influence on the TAN excretion rate. A diurnal rhythm was evident in J. edwardsiiudbut not in P. cygnus. Feeding had a large affect on the TAN excretion rate, with anudapproximate 6-fold increase occurring in each species. The excretion ratesudremained high for over 24 hours post-prandial.udThe effect of the dissolved oxygen level on recovery of P. cygnus from audperiod of activity/emersion was investigated. Based on the rate of recovery ofudvarious physiological parameters (oxygen consumption, haemolymph ammonia,udlactate, glucose, and pH), the maintenance of water oxygen levels close to 100%udsaturation is recommended. Water oxygen levels less than 60% saturation slowedudthe rate of recovery. All lobsters recovering in water with oxygen levels less thanud20% saturation died.udCarrying P. cygnus out of water imposes physiological disturbances to theudlobsters. The severity of the disturbances increased when the relative humidityudwas lower and when wind was present. Spraying water over the lobsters preventsudsome of the physiological consequences of emersion, such as decreases in pH andudhaemolymph ammonia buildup, however it does not prevent haemolymph lactateudincreases. Therefore, lobsters still rely on anaerobic metabolism when emersed inudsprays. There was no evidence that failure of lobsters to recover from a period ofudemersion was caused by gill damage.udA half hour period of emersion/handling at 23°C caused largeudphysiological disturbances of P. cygnus. Halving the emersion/handling time didudnot decrease the extent of the physiological disturbances. Slow-chilling theudlobsters to 11°C prior to emersion/handling, was an effective means of decreasingudthe physiological disturbances associated with emersion. udThis study has developed our understanding of the physiological responsesudof the southern and western rock lobsters to factors affecting them during postcaptureudprocesses, and will allow the design and management of rock lobsterudholding facilities to be based on a sound scientific basis. It also represents a majorudcontribution to knowledge on respiration and nitrogen metabolism of largeuddecapod crustaceans.