Long term roe enhancement of Evechinus chloroticus

Abstract

The effects of roe enhancement on gonad growth and colour, survival, and reproductive development in Evechinus chloroticus were tested in a 27-week experiment. Urchins were collected on 28 July 2006 and held at 14 °C and 12:12 h light/dark in groups of 18 urchins (mean test diameter = 92.6 ± 0.5 mm; mean wet weight = 316.5 ± 5.5 g) per basket and fed ad libitum a formulated moist feed. The urchins were sampled at the beginning of the experiment and every three weeks after, for 27 weeks. The maximum GI value of roe enhanced E. chloroticus is likely to be reached within 12 weeks and the most economic roe enhancement period is likely to be 9 weeks in terms of optimising returns for minimal holding costs. There were no effects on survival from long term roe enhancement and changes in lightness of the gonads of urchins held in the trial occurred as a result of the urchins feeding on the artificial diet rather than being exposed to long term enhancement. The experimental conditions effected the reproductive development of E. chloroticus during the experiment. Although the gonads of the experimental urchins progressed through the reproductive stages at a similar rate to those taken from the wild source population at the same times, the former was less advanced after 12 weeks and more advanced after 27 weeks. The 27-week result is possibly due to the early initiation of the photoperiod cue for gametogenesis during the experiment. The experimental results indicate that the cue for gametogenesis occurs in the wild population in mid September at the latest. The results from this study support the hypothesis that food availability is the strongest driver of gonad enhancement (increase in gonad size) in E. chloroticus, but that other environmental factors have an influence on both gonad size and the gametogenic cycle of this species.