Philip J. James

A comparison of the effect of urchin size and diet on gonad yield and quality in the sea urchin Evechinus chloroticus Valenciennes

We compared the gonad-enhancing effects of two diets (NIWA and NIFA diets) in two size classes of sea urchins (Evechinus chloroticus): small and large urchins with a test diameter of 75.6xa0±xa01.2xa0mm and 93.8xa0±xa00.5xa0mm, weighing 174.8xa0±xa07.9xa0g and 315xa0±xa05.6xa0g, respectively. After eightxa0weeks being fed prepared diets, urchin gonad index (GI) had significantly surpassed that of the initial and final samples of wild urchins. Urchins in the NIWA/small treatment had a larger GI than the NIFA/small and NIFA/large treatments. The NIWA/large treatment had a larger GI than the NIFA/large treatment. The overall percentage increase in GI for the NIWA/small, NIWA/large, NIFA/small and NIFA/large treatments were 183%, 135%, 132% and 85%, respectively. In terms of gonad colour (CIELAB), there were no significant differences in gonad redness (a*) or yellowness (b*) between experimental treatments, but there was a significant difference in gonad lightness (L*) with small urchins fed both diets having lighter-coloured gonads than the large urchins fed both diets. Sensory assessment of gonads revealed that gonads from small urchins fed both diets were rated as being of better colouration and more uniform in colour than gonads from large urchins. Gonads of urchins fed the NIFA diet were rated as being less bitter and of better overall taste than gonads from urchins fed the NIWA diet. This study shows that feeding prepared diets to E. chloroticus can significantly increase gonad yield but that different diets can affect the magnitude of GI increase and the taste of gonads, and that smaller urchins appear more suitable for gonad enhancement.

Evaluation of visible implant fluorescent elastomer (VIE) as a tagging technique for spiny lobsters (Jasus edwardsii)

Tagging crustaceans for growth studies is often difficult because external tags/marks may be shed or cause mortalities during moulting. In this investigation, the effectiveness of visible implant fluorescent elastomer (VIE) as an invasive tagging technique for spiny lobsters (Jasus edwardsii) was investigated over a 6-month period. Tagged lobsters were either tagged with the tag running transversely across the ventral abdominal superficial flexor muscle block (transverse VIE) in the second abdominal segment, or in-line with the ventral abdominal superficial flexor muscle block (longitudinal VIE). Non-tagged lobsters were used as the control. At the conclusion of the investigation there were no differences in growth or survival between tagged lobsters and untagged controls and tag retention rates were 100% for both tagging treatments over the 6-month period. Tag visibility was high after six months in both tagging treatments, although higher in the longitudinal VIE treatment. Tag fragmentation was frequent in the transverse VIE treatment, but infrequent in the longitudinal VIE treatment. We conclude that VIE is an effective tagging technique for J. edwardsii in terms of the high degree of tag visibility, retention, and non-detrimental impact on the growth and survival of tagged animals, provided the VIE tag is injected in-line with the orientation of the muscle fibres/tissue.

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.