PARENT SESSION
1D Bioassays for specific hazards (estrogenic effects, genotoxicity, neurotoxicity, ...)
9:00 AM to 7:00 PM, Tuesday, 08 May 2001

(T/EH031) Effects of different cryoprotectants to oyster gametes and embryos : a preliminary step to establish cryopreservation protocols.

Nascimento, Iracema Andrade¹, Leite, Maria Bernadete Neiva L.¹, de Araujo, Milena Maria Sampaio¹, Sansone, Giovanni², Pereira, Solange Andrade¹, ^{1 2}

ABSTRACT- Aquaculture is a worldwide developing activity. However the progress of this development is dependent on the availability of advanced biotechnology that can provide continuous seed production, regardless of the spawning season, what can reduce the broodstock management costs. Cryopreservation is a valuable solution for this purpose. Besides, it allows the preservation of mutant germe lines or to select broodstock. The benefits of cryopreservation has been demonstrated for mammals and fishes, and some achievements have been reported for invertebrates; however high fragility is reported for oysters, which results confirm that an optimal cryopreservation method developed for one species is not always applicable to gametes or embryos of other species. One of the reasons is the difference in toxicological responses to cryoprotectants. The object of the present study was to determine the toxicological effects on C.rhizophorae gametes and embryos of cryoprotectants such as Dimethyl Sulfoxide (DMSO), Glycerol (G), Ethylene Glycerol (EG), Propylene Glycerol (PG) and Methanol (MET). Gametes (oocytes and spermatozoa) and embryos (trochophorae) were exposed for 10, 20 and 30 minutes to a range of concentrations (5, 10, 15 ou 20%) of those cryoprotectants, as previously utilized for different invertebrate species. The differences between exposition times were not statistically significant (p>0.05). However oyster gametes became increasingly susceptible to the cryoprotectants as their concentrations were increased. The trochophere stage embryos were more resistant to cryoprotectant exposure. Not only the cryoprotectant substances, but also their critical concentrations (EC₅₀ and EC₁) were markedly different for gametes and embryos. For both gametes, G and MET have been more toxic (EC₅₀-24h respectively of 3.46 and 4.52% for oocytes and 2.07 and 11.21% for spermatozoa) than EG, PG or DMSO. For trochophore embryos however, these cryoprotectants, especially PG ,have been more toxic (EC₅₀-24h for PG = 23.56%) than the Glycerol or Methanol.

Key words: cryoprotectant , effects, oyster gametes, oyster embryos