Effects of storage time, sex steroids and media composition on egg viability of rainbow trout (Oncorhynchus mykiss)

The effects of storage time and media composition with or without steroids on the viability of unfertilized eggs from rainbow trout (Oncorhynchus mykiss) were studied. In this study, the percentages of eyed and hatched eggs were used as proxies for egg viability. Unfertilized eggs were stored in coelomic fluid (CF), steroid-free coelomic fluid (SFCF), SFCF + 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P), SFCF + estradiol-17β (E2), SFCF + 11-ketotestosterone (11-KT), artificial media (Cortland), Cortland + SFCF, Cortland + 17,20β-P, Cortland + E2 or Cortland + 11-KT at 4 °C for 0, 4, 7, 10 or 15 days prior to fertilization. Accordingly, viability of eggs tended to decrease during storage for 7 days in all media, as hatching rates decreased from 57 ± 16.8% to 46 ± 16.9%. By 10 days of storage, only eggs in CF were fertilizable, yielding rates of eying and hatching of 38 ± 22.0% and 16 ± 9.3%, respectively. None of the eggs reached the eyed stage when stored for 15 days. The osmolality of media increased and the pH decreased during storage. Water uptake during hardening decreased with storage time. We conclude that natural fluids bathing the eggs of trout are superior in maintaining egg viability than a suite of other media, and that key bioactive steroids do not affect storage. However, storage is impaired in steroid-free CF, suggesting that some unidentified charcoal-adsorbable components in CF are important for maintenance of viability.