Jasmine Nahrgang

Petroleum-derived water-accommodated fractions (WAFs) contain complex mixtures of hydrocarbons and water-soluble compounds. While the toxicity of polycyclic aromatic hydrocarbons (PAHs) is well established, the contribution of more polar compounds to the overall toxicity of the crude oil WAFs remains less understood, but they are still assumed to contribute significantly to the toxicity of the mixtures. In this study, we used an effect-directed analysis (EDA) approach to assessed and compared the biological effects of a WAF extract and its chemical fractions, i.e. saturates, monocyclic aromatic hydrocarbons (MAHs), naphthalenes (NAPs), PAHs, and resins, using luciferase reporter gene assays and gene expression of precision-cut liver slices from Atlantic cod (Gadus morhua). Chemical characterization (GC×GC-MS) revealed a wide array of chemical structures in the WAF extract and its fractions. The resins fraction accounted for the largest number of distinct chemicals (~189), followed by the saturates (~130) and MAHs (~100), whereas the NAPs and PAHs fractions contained fewer compounds (~40 and ~35, respectively). Reporter gene assays revealed that both the WAF extract and the resins fraction induced dose-dependent activation of the Atlantic cod aryl hydrocarbon receptor (gmAhr2a) and zebrafish pregnane X receptor (zfPxr), whereas Atlantic cod estrogen receptor alpha (gmEra) and peroxisome proliferator-activated receptor alpha 1 (gmPpara1) were unresponsive. Consistent with the receptor-mediated responses, the WAF extract and the resins fraction strongly induced mRNA expression of cytochrome P450 1a (cyp1a) in PCLS. In silico toxicity screening of the top 30 most abundant compounds in the resins fraction, resulted in the selection of eight chemicals for single-compound testing of receptor-mediated activity. Among these eight compounds, phenalene-1-one, 7-methyl-2,3-dihydroinden-1-one, and 10H-antracen-9-one, activated one or more receptors. These findings support the hypothesis that the chemically diverse polar resin fraction contributes to the receptor-mediated activity of crude oil WAF, with individual oxygenated constituents likely accounting for part of the observed responses.

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Crude oil and its water-soluble fractions (WSF) are highly toxic to early life stages of fishes, while exposed adults are often considered more resilient. However, research suggests that parental exposure can result in toxic effects in subsequent generations. This study investigated the impact of a crude oil WSF on Atlantic cod ( Gadus morhua ) broodstock and the subsequent maternal effects on their offspring. Mature Atlantic cod at late gametogenesis were exposed for 20 days to either a crude oil WSF or to control conditions. Over the following month, fish from both groups were repeatedly strip-spawned, and egg batches were fertilized in vitro using pooled sperm from control males. Maternally exposed offspring had accumulated levels of petroleum-derived aromatic hydrocarbons, including monoaromatic and polyaromatic hydrocarbons (PAHs). However, the profile of accumulated compounds was skewed towards lower-molecular weight compounds compared to the exposure water. Crude oil WSF exposure appeared to accelerate spawning readiness in females, resulting in smaller egg diameters in strip-spawned eggs. Additionally, sperm from oil-exposed males showed reduced curvilinear velocity and linearity. Despite these impacts, no significant differences in larval malformations or cardiac activity were observed. Our findings highlight the importance of advancing our understanding of intergenerational impacts of crude oil contamination on key fish species to accurately assess the long-term ecological consequences of petroleum pollution.

Crude oil-derived water-accommodated fractions (WAFs) are complex mixtures containing bioavailable constituents. We applied an automated zebrafish behavior-based assay to assess potential neuroactivity following exposure to WAF and chemical fractions including polycyclic aromatic hydrocarbons (PAHs), resin, naphthalene (NAP), monoaromatic hydrocarbon (MAH), and saturate fractions. Zebrafish larvae were exposed to WAF concentrations (9.8-100%, 1 g/L loading) and assessed using the 26-end point visual and acoustic motor response assay at 5 day postfertilization. WAF exposure elicited concentration-dependent behavioral effects, including reduced dark-period activity, impaired acoustic startle responses, and inappropriate activity during light and typically quiescent interstimulus periods. All WAF fractions were neuroactive, eliciting dark-phase hypoactivity and fraction-specific hyperactivity patterns. Exposure to PAH, MAH, or NAP fractions also impaired habituation learning. Comprehensive two-dimensional gas chromatography-mass spectrometry identified phenanthrene, 2-methylanthracene, and ethyl 4-ethoxybenzoate as the dominant PAHs. In contrast, the resin fraction was chemically diverse. Behavioral profiles of zebrafish exposed to PAH fraction constituents or an artificial mixture recapitulated WAF-like effects. Neurobehavioral fingerprinting predicted that WAF neuroactivity may arise from structurally diverse chemical classes disrupting multiple molecular targets, including disruption of peroxisome proliferator-activated receptor delta- or gamma-aminobutyric acid type A receptor-dependent signaling. Taken together, integration of chemical fractionation, high-resolution behavior phenotyping, and mode-of-action fingerprinting supports mechanistic dissection of environmentally relevant mixtures.

Magnetic resonance imaging (MRI) was applied to determine the sex of polar cod (Boreogadus saida Lepechin, 1774) (Actinopterygii: Gadidae) and to follow the gonadal development in individual animals over time. Individual unanaesthetised fish were transferred to a measurement chamber inside a preclinical 9.4 T MRI scanner and continuously perfused with aerated seawater. A screening procedure at an average of 3.5 h, consisting of a set of MRI scans of different orientations, was repeated every 4 weeks on the same set of reproducing B. saida (n = 10) with a body length of about 20 cm. Adapted multi‐slice flow‐compensated fast low‐angle shot (FcFLASH) and rapid acquisition with relaxation enhancement (RARE) protocols with an in‐plane resolution of 313 μm and an acquisition time of 2.5 min were used to visualise the morphology of various organs, including the gonads within the field of view (FOV). The MR images provided high resolution, enabling specific sex determination, calculation of gonad volumes, and determination of oocyte sizes. Gonad maturation was followed over 4 months from November 2021 until shortly before spawning in February 2022. The gonad volume increased by 2.3–25.5% for males and by 11.5–760.7% for females during the observation period. From October to February, the oocyte diameter increased from 427 μm (n = 1) to 1346 ± 27 μm (n = 4). Interestingly, individual oocytes showed changes in MR contrast over time that can be attributed to the morphological development of the oocytes. The results fit well with previous literature data from classical invasive studies. The presented approach has great potential for various ecophysiological applications such as monitoring natural or delayed development of internal organs or sex determination under different environmental conditions.

Genomic rearrangements have in recent years gained attention due to their evolutionary role in processes related to adaptation to local environmental conditions as well as diversification and speciation. In this study, we report on genomic rearrangements in the cold-water adapted polar cod ( Boreogadus saida ), a keystone Arctic fish species. By taking advantage of a new chromosome-level genome assembly in combination with whole-genome population sequencing data from specimens across the northern Barents Sea and adjacent regions, we identified a substantial number of larger chromosomal inversions (n=20) and characterized the previously identified chromosomal fusions (n=5). These genomic features — encompassing over 20% of the genome — exhibited genetic divergence, strong internal linkage disequilibrium, and signals of selection. Two of the identified inversions were associated with the two previously described hemoglobin clusters, while a third chromosomal region was found to differentiate between males and females. Moreover, clustering analyses on genotype frequencies of inversions revealed sub- structuring according to five geographic sub-groups suggesting sub-populations and/or the existence of cryptic ecotypes. These results provide novel insights into the impact of genomic rearrangements in population divergence and thus, potentially local adaptation, especially in species with high gene flow.

Fish early life stages are well known for their sensitivity to crude oil exposure. However, the effect of crude oil exposure on adults and their gametes during their spawning period is not well studied. Polar cod, a key arctic fish, may be at risk for crude oil exposure during this potentially sensitive life stage. Additionally, this species experiences lower food availability during their spawning season, with unknown combined consequences. In the present study, wild-caught polar cod were exposed to decreasing levels of a water-soluble fraction (WSF) of crude oil or control conditions and fed either at a low or high feed ration to assess the combined effect of both stressors. Samples were taken during late gonadal development, during active spawning (spawning window), and in the post-spawning period. Histology analysis of gonads from fish sampled during the spawning window showed that oil-exposed polar cod were more likely to have spawned compared to controls. Oil-exposed females had 947 differentially regulated hepatic genes, and their eggs had a higher polycyclic aromatic hydrocarbon body burden compared to controls. Feed ration did not consistently affect polar cod's response to oil exposure for the endpoints measured, however, did alone result in decreases in some sperm motility parameters. These results suggest that polar cod's spawning period is a sensitive life event to crude oil exposure, while feed limitation may play a minor role for this supposedly capital breeder. The effects of adult exposure to crude oil on gamete quality and the next generation warrant further investigation.

The rise in offshore oil and gas operations, maritime shipping, and tourism in northern latitudes enhances the risk of oil spills to sub-Arctic and Arctic coastal environments. Therefore, there is a need to understand the potential adverse effects of petroleum on key species in these areas. Here, we investigated the effects of oil exposure on the early life stages of capelin (Mallotus villosus), an ecologically and commercially important Barents Sea forage fish species that spawns along the coast of Northern Norway. Capelin embryos were exposed to five different concentrations (corresponding to 0.5–19 µg/L total PAHs) of water-soluble fraction (WSF) of crude oil from 6 days post fertilization (dpf) until hatch (25 dpf), and development of larvae in clean seawater was monitored until 52 dpf. None of the investigated endpoints (embryo development, larval length, heart rate, arrhythmia, and larval mortality) showed any effects. Our results suggest that the early life stages of capelin may be more robust to crude oil exposure than similar life stages of other fish species.