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

Abstract

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.Embryos exposed to 10mgL−1 total ammonia (TA-N), which corresponded to unionized ammonia (UIA-N) concentrations ranging between 0.307 and 0.468mgL−1 in the conditions of the experiment, exhibited significantly reduced hatch rates and complete mortality between 3 and 4days pf; the latter period corresponds to the onset of exogenous feeding of red snapper. In contrast, control groups (TA-N<0.26mgL−1, UIA-N<0.006mgL−1) maintained high survival rates beyond 5days pf indicating potential to successfully initiate exogenous feeding. Exposure to 1mgL−1 TA-N (0.020mgL−1<UIA-N<0.054mgL−1) did not alter significantly survival with respect to control groups. Significant interactions between the spawn and the tolerance to hypoxia or elevated ammonia were detected in both experiments, indicating that variations among spawns need to be accounted for when determining safe levels for hatchery production. Statement of relevanceAchieving a reliable supply of high quality eggs and larvae is one of the main challenges of the developing marine aquaculture industry.Most studies to date have focused on maternal determinants of egg quality but the viability of embryos and newly hatched larvae can be impacted after fertilization if environmental conditions become unfavorable due to intensive hatchery conditions; this topic is poorly documented in marine fishes to date.This study provides data on the effects of two major stressors acting under high density culture (hypoxia and elevated ammonia concentration) on embryos and newly hatched larvae of the red snapper; the results highlight the importance to consider variations among spawns/parents when determining safe levels for hatchery production and also the high sensitivity of red snapper to these stresses, suggesting that this topic should be investigated in other marine offshore species.Relevance of the research to commercial aquaculture.The research contributes to control egg quality.