Environmental parameters

Throughout the course of this study, it was evident that the quality of phyllosoma differed dependant upon various environmental, physiological and nutritional factors primarily resulting from conditions that broodstock were subjected to. One of the early findings demonstrated that while elevated

temperatures accelerated embryonic development, reduced the incubation period by almost one-half and increased the duration of larval availability by 2 months (Tong et al., 2000; Smith et al., 2002), this was achieved to the detriment of larval competency (Chapter 2). The definition of larval competency used during this study is based on the survival and growth potential of larvae. This is especially

se en

les bient incubated animals. This is a situation

is

wi he impact of size may not be as

are

population. To date, poor larval survival has also been demonstrated in captivity

an

temperature to artificially reduce the period of embryonic development and as a consequence, produce smaller less competent phyllosoma larvae. The emphasis on the production of out-of-season larvae should instead be focused on phase shifting groups of broodstock to produce larvae at different times of the year under

simulated ambient conditions. Such a regime may involve having a group of broodstock 6 months out-of-phase with the normal ambient season. A 6-month pertinent when selecting J. edwardsii larvae for culture, where the larval pha

compasses 11 moult stages, numerous instars and takes in excess of 300 days to complete (Kittaka, 1994). During this study it was found that the use of elevated embryonic temperatures had the adverse effect of producing smaller larvae that are

s likely to survive compared to am

that is further exacerbated by culture, as the typical growth pattern for crustaceans for body size post-ecdysis to be proportional to the size of their previous exoskeleton (Kunish and Anger, 1984; Lovrich and Vinuesa, 1995). In a species

th a shorter and less complex life history t

significant. In their natural environment the odds of J. edwardsii larvae surviving low, with a life-time egg production of 1.6 x 106 (Pollock, 1997) from which only one male and female need to survive to maturity to maintain a stable wild

and poses a significant impasse to closing the life-cycle of J. edwardsii. Therefore, it is essential that efforts to raise larvae are concentrated on producing the largest

out-of-phase season could be achieved in a controlled environment whereby the changes in water temperature and photoperiod, major cues for maturation in crustaceans, that would occur during a 12-month ambient period (9.5 - 18ºC and 8.5 – 15.3 h daylight, respectively), would be slowed to take 18 months to complete. This would effectively place this group of broodstock 6 months out-of- phase with the ambient season. At this time a 12-month temperature and photo period cycle would be reverted to, albiet 6 months out-of-phase with ambient conditions. Similarly, groups of broodstock may be shifted to 3 and 9 months out- of-phase if desired.

9.1.3. Physiological parameters

There were a number of physiological determinants of larval competency noted during this study (Chapter 3). Predominant among these was establishing that large females produce large competent phyllosoma compared to those from smaller females. Why this occurs is not obvious although theories such as the

establishment of a hierarchical system whereby large females have preferential access to food, shelter and males (MacDiarmid, 1989; MacDiarmid and Kittaka, 2000) may contribute to an explanation. As a consequence, a preliminary step to producing viable phyllosoma should include the targeting of large broodstock in preference to smaller animals.

The range of morphological changes that occurred at maturity were similar to those experienced in other spiny lobster species (Kubo, 1938; Gordon, 1960; Berry, 1971), in spite of apparent precocious maturation of females in captivity. This suggests that the alteration of certain morphological traits by J. edwardsii at maturity i.e., the elongation of the walking legs in males and the increased length and width of the abdominal segment in females, are secondary sexual

characteristics initiated or preceded by maturation cues. Cues that initiate

maturation are undefined in this and most crustacean species, however it has been suggested that size at onset of maturity may be influenced by various

1993). This is a fertile area of research worth pursuing for those interested in maintaining somatic growth rather than inducing reproductive development.

The smaller number of viable phyllosoma obtained at hatch compared to the predicted egg number (Chapter 3) raises a number of questions that should be addressed with future studies. The prominent question: Is the large reduction in fecundity representative of what occurs in the wild, i.e., is this normal, or is it the result of hatchery practices?” If the latter is found to be primarily responsible for the reduction in viable phyllosoma at hatch, many of the current animal husbandry processes will need to be examined with a view to minimizing losses and perhaps reducing their impact upon those larvae that are hatching. However, these losses may also occur in the wild, in which case the traditional estimate of fecundity based on egg numbers needs to be reassessed downwards.