Abstract:
A series of experiments testing the effects of seasonality, temperature and photoperiod were carried out to investigate the effects of biotic (gametogenesis) and abiotic factors (temperature and photoperiod) on roe enhancement of Evechinus chloroticus. Urchins were collected and held at 10, 14 and 18 °C and in 6, 12 and 18 h light in three 10-week experiments during spring, summer and winter. Groups of 20 urchins (mean test diameter = 85.9 ± 0.2 mm; mean wet weight = 264.4 ± 1.5 g) were held in baskets and fed ad libitum a formulated moist feed. Seasonal effects on the final urchin gonad index (GI) of each experiment reflected the initial GI of the urchins at the beginning of each experiment. There were seasonal effects observed for the increase in GI values in the experimental urchins but these were restricted to a slightly higher increase in GI in summer. Urchins held at 18 °C had significantly higher GI values and larger increases in GI than those held at 14 °C, except in summer when there was no significant difference between the final GI values of these two temperature treatments. Urchins held at 14 °C had significantly greater gonad growth and increase in GI than those held at 10 °C in each of the three experiments. In terms of the economics of roe enhancement, the benefits of increases in GI must be weighed against any increase in holding temperatures in land-based holding systems, or in transporting urchins to sites with warmer ambient temperatures in sea-based holding systems. Photoperiod appeared to have no effect on gonad growth except in summer when the short day treatment (6 h L) had significantly lower GI and increase in GI than the other treatments (12 or 18 h L). Season had an effect on gonad colour, temperature had a limited effect on gonad yellowness and photoperiod had no effect. None of the experimental factors had a significant effect on urchin survival. The reproductive stage of the experimental urchins advanced with increasing temperature. Seasonal changes in the reproductive cycle of E. chloroticus do not appear to have a significant effect on gonad growth other than during periods when there is a high percentage of urchins in the “spent” stage (summer).