Assessment of early life stage mahi-mahi windows of sensitivity during acute exposures to Deepwater Horizon crude oil.

Windows of exposure to a weathered Deepwater Horizon oil sample (slick A) were examined for early life stage mahi-mahi (Coryphaena hippurus) to determine whether there are developmental periods of enhanced sensitivity during the course of a standard 96-h bioassay. Survival was assessed at 96 h following oil exposures ranging from 2 h to 96 h and targeting 3 general periods of development, namely the prehatch phase, the period surrounding hatch, and the posthatch phase. In addition, 3 different oil preparations were used: high- and low-energy water accommodated fractions of oil and very thin surface slicks of oil (∼1 µm). The latter 2 were used to distinguish between effects due to direct contact with the slick itself and the water underlying the slick. Considering the data from all 3 exposure regimes, it was determined that the period near or including hatch was likely the most sensitive. Furthermore, toxicity was not enhanced by direct contact with slick oil. These findings are environmentally relevant given that the concentrations of polycyclic aromatic hydrocarbons eliciting mortality from exposures during the sensitive periods of development were below or near concentrations measured during the active spill phase. Environ Toxicol Chem 2017;36:1887-1895. © 2016 SETAC.

A novel system for embryo-larval toxicity testing of pelagic fish: Applications for impact assessment of Deepwater Horizon crude oil.

Key differences in the developmental process of pelagic fish embryos, in comparison to embryos of standard test fish species, present challenges to obtaining sufficient control survival needed to successfully perform traditional toxicity testing bioassays. Many of these challenges relate to the change in buoyancy, from positive to negative, of pelagic fish embryos that occurs just prior to hatch. A novel exposure system, the pelagic embryo-larval exposure chamber (PELEC), has been developed to conduct successful bioassays on the early life stages (ELSs; embryos/larvae) of pelagic fish. Using this unique recirculating upwelling system, it was possible to significantly improve control survival in pelagic fish ELS bioassays compared to commonly used static exposure methods. Results demonstrate that control performance of mahi-mahi (Coryphaena hippurus) embryos in the PELEC system, measured as percent survival after 96-hrs, significantly outperformed agitated static exposure and static exposure systems. Similar significant improvements in 72-hr control survival were obtained with yellowfin tuna (Thunnus albacares). The PELEC system was subsequently used to test the effects of photo-induced toxicity of crude oil to mahi-mahi ELSs over the course of 96-hrs. Results indicate a greater than 9-fold increase in toxicity of Deepwater Horizon (DWH) crude oil during co-exposure to ambient sunlight compared to filtered ambient sunlight, revealing the importance of including natural sunlight in 96-hr DWH crude oil bioassays as well as the PELEC system's potential application in ecotoxicological assessments.

Acute embryonic or juvenile exposure to Deepwater Horizon crude oil impairs the swimming performance of mahi-mahi (Coryphaena hippurus).

The Deepwater Horizon incident likely resulted in exposure of commercially and ecologically important fish species to crude oil during the sensitive early life stages. We show that brief exposure of a water-accommodated fraction of oil from the spill to mahi-mahi as juveniles, or as embryos/larvae that were then raised for ∼25 days to juveniles, reduces their swimming performance. These physiological deficits, likely attributable to polycyclic aromatic hydrocarbons (PAHs), occurred at environmentally realistic exposure concentrations. Specifically, a 48 h exposure of 1.2 ± 0.6 µg L(-1) ΣPAHs (geometric mean ± SEM) to embryos/larvae that were then raised to juvenile stage or a 24 h exposure of 30 ± 7 µg L(-1) ΣPAHs (geometric mean ± SEM) directly to juveniles resulted in 37% and 22% decreases in critical swimming velocities (Ucrit), respectively. Oil-exposed larvae from the 48 h exposure showed a 4.5-fold increase in the incidence of pericardial and yolk sac edema relative to controls. However, this larval cardiotoxicity did not manifest in a reduced aerobic scope in the surviving juveniles. Instead, respirometric analyses point to a reduction in swimming efficiency as a potential alternative or contributing mechanism for the observed decreases in Ucrit.

Effects of potassium ion supplementation on survival and ion regulation in Gulf killifish Fundulus grandis larvae reared in ion deficient saline waters.

Teleost fish often live in an environment in which osmoregulatory mechanisms are critical for survival and largely unknown in larval fish. The effects of a single important marine ion (K(+)) on survival and ion regulation of larval Gulf killifish, an estuarine, euryhaline teleost, were determined. A four-week study was completed in four separate recirculating systems with newly hatched larvae. Salinity in all four systems was maintained between 9.5 and 10‰. Two systems were maintained using crystal salt (99.6% NaCl) with K(+) supplementation (1.31±0.04mmol/L and 2.06±0.04mmol/L K(+); mean±SEM), one was maintained with crystal salt and no K(+) supplementation (0.33±0.05mmol/L K(+)), the fourth system was maintained using a standard marine mix salt (2.96±0.04mmol/L K(+)), the salt mix also included standard ranges of other ions such as calcium and magnesium. Larvae were sampled throughout the experiment for dry mass, Na(+)/K(+)-ATPase (NKA) activity, whole body ion composition, relative gene expression (NKA, Na(+)/K(+)/2Cl(-) cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR)), and immunocytochemistry staining for NKA, NKCC, and CFTR. Larvae stocked into water with no K(+) supplementation resulted in 100% mortality within 24h. Mortality and dry mass were significantly influenced by K(+) concentration (P≤0.05). No differences were observed among treatment groups for NKA activity. At 1dph NKA mRNA expression was higher in the 0.3mmol [K(+)] group than in other treatment groups and at 7dph differences in intestinal NKA and CFTR staining were observed. These data indicate that the rearing of larval Gulf killifish may be possible in ion deficient water utilizing specific ion supplementation.