Michael P. Bruce

Lipid reserves used by pueruli of the spiny lobster Jasus edwardsii in crossing the continental shelf of New Zealand

Lipid is known to fuel the movement of the nektonic puerulus stage of the spiny lobster Jasus edwardsii across the continental shelf of New Zealand. Lipid class analysis of pueruli caught from two locations across the continental shelf showed that phospholipid predominated (86-96% of total lipid), with only smaller proportions of sterol (0.9-8.7%) and diacylglycerol (1.2-7.6%). Only traces of triacylglycerol, hydrocarbon and wax ester were present (<0.1% of total lipid). Comparison of the lipid class content of pueruli caught onshore and offshore showed that phospholipid reserves are primarily utilised during this important phase in the lifecycle and that diacylglycerol plays a less significant secondary role. Histology identified concentrations of phospholipid in fat bodies located in the haemocoel. The use of phospholipid as the dominant storage medium in the puerulus stage is unlike many other marine taxa, including crustacea, which tend to use triacylglycerol and wax ester. The use of phospholipid as a storage medium may well be related to its characteristic transparency, an important feature of this nektonic stage of lobster development that is highly vulnerable to pelagic visual predators.

Developing yellowtail kingfish (Seriola lalandi) and hāpuku (Polyprion oxygeneios) for New Zealand aquaculture

Two high value species, yellowtail kingfish (Seriola lalandi) and hāpuku (groper, Polyprion oxygeneios), have been identified as suitable new candidates for New Zealand aquaculture. This paper reviews the research by NIWA and collaborators conducted to test the biological, technological and economic feasibility of farming these two species. NIWA now has the capability to produce sufficient kingfish fingerlings per year to meet the needs of the early stages of an industry. Advances in hāpuku aquaculture have also been significant, from spawning in captivity through to the selection of juveniles for improved growth. Recently, the first spawning of captive hāpuku F1 broodstock and production of F2 eggs, larvae and juveniles was achieved. Although hāpuku larval survival remains variable, the ability to close the life cycle, and the availability of domesticated broodstock, provide a significant step forward and increase the chances of this species being commercially farmed.

Accommodating the cost of growth and swimming in fish-the applicability of exercise-induced growth to juvenile hapuku (Polyprion oxygeneios).

Induced-swimming can improve the growth and feed conversion efficiency of finfish aquaculture species, such as salmonids and Seriola sp., but some species, such as Atlantic cod, show no or a negative productivity response to exercise. As a possible explanation for these species-specific differences, a recent hypothesis proposed that the applicability of exercise training, as well as the exercise regime for optimal growth gain (ERopt growth), was dependent upon the size of available aerobic metabolic scope (AMS). This study aimed to test this hypothesis by measuring the growth and swimming metabolism of hapuku, Polyprion oxygeneios, to different exercise regimes and then reconciling the metabolic costs of swimming and specific dynamic action (SDA) against AMS. Two 8-week growth trials were conducted with ERs of 0.0, 0.25, 0.5, 0.75, 1, and 1.5 body lengths per second (BL s−1). Fish in the first trial showed a modest 4.8% increase in SGR over static controls in the region 0.5–0.75 BL s−1 whereas the fish in trial 2 showed no significant effect of ER on growth performance. Reconciling the SDA of hapuku with the metabolic costs of swimming showed that hapuku AMS is sufficient to support growth and swimming at all ERs. The current study therefore suggests that exercise-induced growth is independent of AMS and is driven by other factors.

Temperature effects on the embryo development and hatching of the spiny lobster Sagmariasus verreauxi

Abstract Factors affecting the development of the embryos and production of larvae of the spiny lobster Sagmariasus verreauxi were investigated. Mature lobsters were collected from the fishery in New Zealand and held in captivity until they moulted, mated, and extruded eggs. For females, moulting took place in winter (July/August) and mating occurred 58–88 days later in early spring. The ovigerous females were then held at three temperatures and embryo development monitored at approximately weekly intervals. Mean times to hatch were 55, 75, and 130 days at 20°C, 17°C, and 13°C respectively. The total number of larvae that hatched from each female ranged from 0.97 to 1.4 million. The theoretical temperature at which embryo development ceases (a biological zero) for S. verreauxi, of 9.4°C, was calculated from data on the appearance of the median eye, the eyes and the chromatophores, and the time to hatch. An eye index formula was also derived to allow prediction of time to hatch at a range of temperatures using the cumulative difference between the rearing temperature and the biological zero. First instar phyllosomas from embryos reared at 20°C were significantly smaller than those from 17°C and 13°C but there was no significant difference in fitness. This study shows that hatching can be spread over a number of months, without significantly affecting larval quality, simply by manipulating holding temperature.

Exercise training reduces the flesh firmness of juvenile hāpuku (Polyprion oxygeneios) with a hypertrophic reduction in muscle fibre density

Consumers base the organoleptic quality of fish on factors such as texture, which can be altered by exercise. The effect of exercise on the fillet firmness of hāpuku (Polyprion oxygeneios) was investigated to determine whether exercise would yield a firmer and more desirable product. To achieve this, the firmness and muscle fibre density (MFD) of fillets from fish exercised for 8 weeks at 0.0, 0.75 or 1.5 body lengths/second (BL s−1) was assessed. Firmness was significantly lower in the 0.75 BL s−1 and 1.5 BL s−1 exercised fish than the 0.0 BL s−1 group. MFD was also significantly lower in the exercise treatments. This is explained by an increase in the median fibre size with exercise implying that exercise stimulated muscle fibre hypertrophy, leading to lowered MFD. Assuming that firmer flesh is perceived to be more desirable, exercise may have little value in the production of hāpuku.