Survival of ovulated oocytes of the European catfish

Survival of Silurus glanis ovulated oocytes (ova) measured by the capacity of normal development i.e. percentage of normal and abnormal hatched larvae after in vivo and in vitro storage and exposure to sperm activating or immobilizing solutions and urine was studied. In the case of ovulated oocytes left in the ovaries, total hatching and abnormal hatched larvae (in % of hatching) were respectively 74 and 8.2% immediately after ovulation, 77 and 8.6% after 2 h, 54 and 18% after 4 h, and 38 and 50% after 6 h of storage. Four and 6 h stay of ovulated oocytes in ovaries resulted in a significant increase of abnormal hatched larvae (p < 0.01). For the ova stored in vitro, the capacity to undertake a full embryonic development after fertilization was not significantly changed either after 8.5 h at 19 °C or 3.5 h at 25 °C; there was no ova survival at all after 3.5 h storage at 8 °C, 12 h at 19 °C and 8.5 h at 25 °C. There was a significant increase of abnormal larvae after 3.5 h at 25 °C (74%, p < 0.001) and after 8.5 h at 19 °C (37%, p < 0.05). Exposure of non inseminated ova to water buffered to pH 7.0 (5 mM Tris-HCl) to sperm activating solution (17 or 41 mM NaCl, 5 mM Tris-HCl, pH 8.0) or to immobilizing solution (200 mM NaCl, 30 mM Tris-HCl, pH 7.0) resulted in a regular and rapid decrease of their capacity of development; this was 10% of normal hatched larvae within 4 min in water, and within 6-8 min in the NaCl solutions. A similar situation was observed after exposure to urine with a loss of embryonic development of 30% within 3 min. These results indicate that all steps of the whole procedure of gamete collection and artificial insemination should be carried out rapidly as soon as possible after ovulation.