LOPEZ, J.P.; PODRABSKY, J.E.; SOMERO, G.N.: Anoxia-induced Quiescence in Embryos of The Annual Killifish Austrofundulus limnaeus

The annual killifish Austrofundulus limnaeus inhabits ephemeral ponds in the coastal desert of the Maracaibo basin in Venezuela. Embryos of A. limnaeus are deposited into the muddy substrate of these ponds and are thus likely exposed to severe hypoxia or anoxia during development. To investigate anoxia tolerance, embryos at various developmental stages between fertilization and diapause II were sealed into glass bottles filled with anoxic (nitrogen purged) embryo medium containing 0.5 mg/ml sodium sulfite. Treatments of differing concentrations of sodium sulfite had no significant effects on survivorship. Survival and rate of development were quantified at various time points during a 90 day exposure to anoxia at 25�C. Development is arrested during exposure to anoxia as evidenced by a lack of developmental progress even after extended incubations in anoxic medium. Survival was correlated with the developmental stage of the embryos. Tolerance in early embryos (1 and 2 days postfertilization) was lowest with LT50 values of 1.0 � 0.05 (mean � S.E.M.) and 0.84 � 0.02 days, respectively. Embryos in diapause II had the highest tolerance of anoxia with a mean LT50 of 74.5 � 5.5 days. After 90 days of anoxia, survivorship of diapause II embryos was 33%. Survival after one week of normoxic recovery was similar to initial survival values for exposures less than 30 days. Longer exposures caused a significant decrease in recovery. The extended survival of embryos in diapause II may be related to the pronounced metabolic depression associated with this developmental stage. The mechanisms that support extended survival of anoxia remain unknown. This study indicates that embryos of A. limnaeus may be the most anoxia tolerant vertebrate yet described.