five raja species are displayed in the ‘ray reef’ at dolfinarium harderwijk and, from 1993–2001, 41,772 eggs were laid, of which 39% contained a yolk sac and 3% hatched successfully. different egg-laying periods were distinguished between species. no annual differences in the egg-laying period were observed for raja microocellata, while hatching periods, and thus incubation periods (4.8–7.0 months), differed significantly. no correlation between seawater temperature and incubation time was found.