From Transcriptomic Dysregulation to Behavioral Impairment: Mechanistic Effects of Weathered Brazilian Oil on Early Life Stage Fish

Abstract The 2019–2020 oil spill along the northeastern coast of Brazil affected coastal reef ecosystems and the organisms that inhabit these environments. To characterize the toxicity of persistent weathered oil residues to early life stage fish, embryonic zebrafish (Danio rerio) were exposed to environmentally relevant concentrations of a water-accommodated fraction (WAF) prepared from weathered oil recovered following the spill. Embryos were exposed from 24 to 168 h postfertilization (hpf) to low (2.14 μg ∑PAH60 L–1) and high (17.1 μg ∑PAH60 L–1) concentrations representative of chronic postspill exposure conditions. Transcriptomic profiling revealed early alterations in pathways associated with connective tissue, cardiovascular, and respiratory development at 48 hpf, which corresponded with a significant reduction in heart rate at 72 hpf. By 96 and 168 hpf, molecular responses shifted toward visual system dysfunction, including pathways related to photoreceptor development and phototransduction. Histological evaluation confirmed significant thinning of retinal layers, consistent with impaired retinal development or photoreceptor degeneration. These structural changes translated to functional impairment, as larvae exhibited a 40% reduction in optokinetic response. These integrated analyses identify mechanistic targets of weathered oil toxicity and establish molecular to behavioral relationships that improve understanding of chronic oil spill impacts on early life stage fish.