3.2. Fertilization and hatching rates
The average fertilization rate was 98 ± 1% with no significant difference between treatments. The average hatching rate was 85 ± 2% and no significant differences between treatments were observed. These values are similar to those observed in previous studies where the same spawning trigger was used (Liu et al., 2007).
3.3. Histology
Both diets supported development of ovaries and testes over the trial period with no significant differences between treatments and, at the end of the trial, all induced-individuals produced viable gametes as demonstrated by the high fertilization rate obtained in both treatments. As no significant difference between treatments was recorded, histology data from individuals in the two treatment groups were pooled in order to describe gametogenesis of the entire population under the experimental conditions. At the beginning of the trial the majority of individuals (90%) were found to be at the recovery stage (stage I) with a few individuals still in the spent stage (stage VI). At day 30 the population was less homogeneous and 10% of the individuals were still at stage I, whereas the rest were equally divided between stage II and III. By day 60 most of the urchin population (75%) was in stage III with the remainder at stage II and at day 90 only 30% were still at stage III while 70% progressed to stage IV (Fig. 1).