Effects of hypoxia and elevated ammonia concentration on the viability of red snapper embryos and early larvae

The effects of hypoxic conditions and elevated ammonia concentrations on the viability of embryos and newly hatched larvae of the red snapper (Lutjanus campechanus) were investigated. In all experiments, tested levels of hypoxia or ammonia concentrations were applied to embryos and unfed newly hatched larvae from three different spawns. Exposures began at 1h post fertilization (pf) and lasted until all individuals in a group had expired. Survival rates were monitored daily in duplicates for each spawn in each treatment. Fertilized eggs exposed to 2mgL−1 dissolved oxygen (29% saturation) showed complete mortality before hatch while 81% of embryos in control groups (>85% saturation) hatched and subsequently maintained high survival until 5days pf. Exposure to a moderate hypoxia (target 3mgL−1, 43% saturation) reduced significantly the hatch rate and subsequent survival rates; the magnitude of the difference in survival rate between control and exposed groups increased from 10% at hatch to 45% at 5days pf. When oxygen concentration was maintained high (83% saturation) until 36h pf and then progressively reduced to reach 3mgL−1 at 2days pf, the survival of exposed embryos and larvae did not differ significantly from those recorded in control groups, although potential delayed or cumulative effects of the treatment after 4days pf could not be evaluated in this experiment.