Environmental physiology of cultured early-stage southern rock lobster (Jasus edwardsii Hutton, 1875) larvae

The aim of this project was to define more clearly the culture conditions for the propagation of the southern rock lobster (Jasus echvardsii) in relation to environmental bioenergetic constraints. The effects of temperature and photoperiod on the first three stages of development were first studied in small-scale culture experiments. Larvae reared at 18°C developed faster and reached a larger size at stage IV than larvae cultured at 14°C. Development through stage II was shorter under continuous light. However, the pattern of response to photoperiod shifted at stage III when growth was highest in all the light/dark phase treatments than under continuous light. The influence of temperature and light intensity in early-stage larvae was further investigated through behavioural and physiological studies. Results obtained in stages I, II and III larvae indicated an energetic imbalance at high temperature (~22°C). The behavioural response of stage I larvae to light intensity suggested that light may be used to control behaviour in culture conditions. Early-stage larvae showed higher oxygen consumption, nitrogen excretion, and feed intake under light than in the dark. This may be due to the demonstrated increased activity under light conditions. A technique based on the chemical immobilisation of larvae was developed to assess the effect of temperature on the standard metabolic rate and the energetic cost of swimming in phyllosomas. Estimates of larval locomotor activity at different temperatures obtained through measurements of oxygen consumption were in agreement with behavioural response under the same conditions. The water quality requirements off. edwardsii larvae were determined for dissolved oxygen, salinity, and ammonia. A critical oxygen tension of `4.3` `ml` `O_2` `1^-1` was found for stage I larvae at 18°C. Stage I larvae were found to be stenohaline and a 3 ppt departure from normal salinity (34 ppt) during culture had a significant effect on growth. The cost of osmoregulation was examined in newly-hatched larvae and in stage I phyllosomas acclimated or not to sub-normal salinities. Safe levels of total ammonia concentration determined for stages I, II, III, and IV were `2.65` `mg` `1^-1`, `3.83` `mg` `1^-1`, `4.37` `mg` `1^-1`, and `2.98` `mg` `1^-1`, respectively. The results documented throughout this thesis highlighted the significance of environmental manipulation to achieve greater survival and growth during the larval development of J. edwardsii. In addition, information on the environmental physiology and behaviour of early-stage larvae provided an insight into an integrated approach, which at term will allow for the definition of system and dietary requirements of all developmental stages.