Transcriptomic responses and apoptosis in larval red drum (Sciaenops ocellatus) co-exposed to crude oil and ultraviolet (UV) radiation.

Ultraviolet (UV) radiation can significantly increase the toxicity of polycyclic aromatic hydrocarbons (PAHs) in crude oil to early life stage (ELS) fishes through photo-induced /photo-enhanced toxicity. However, little is known about the sub-lethal effects and mechanisms of photo-induced PAH toxicity in ELS fishes. The present study investigated apoptosis and global transcriptomic effects in larval red drum (Sciaenops ocellatus) (24-72 h post-fertilization) following co-exposure to oil (0.29-0.30 µg/L ∑PAH50) and UV. Apoptosis was quantified using the TUNEL assay, and transcriptomic effects were assessed using RNA sequencing analysis. Apoptotic fluorescence was greatest in the eyes and skin following 24 and 48 h co-exposure to oil and UV, indicating photo-induced toxicity. Consistent with these phenotypic responses, pathways associated with phototransduction, eye development, and dermatological disease were among the top predicted pathways impacted. The present study is the first to provide global transcriptomic analysis of UV and oil co-exposure in an ELS fish.

Exposure to Crude Oil Induces Retinal Apoptosis and Impairs Visual Function in Fish.

Polycyclic aromatic hydrocarbons (PAHs) present in crude oil are known to impair visual development in fish. However, the underlying mechanism of PAH-induced toxicity to the visual system of fish is not understood. Embryonic zebrafish (Danio rerio) at 4 h post fertilization were exposed to weathered crude oil and assessed for visual function using an optokinetic response, with subsequent samples taken for immunohistochemistry and gene expression analysis. Cardiotoxicity was also assessed by measuring the heart rate, stroke volume, and cardiac output, as cardiac performance has been proposed to be a contributing factor to eye-associated malformations following oil exposure. Larvae exposed to the highest concentrations of crude oil (89.8 µg/L) exhibited an increased occurrence of bradycardia, though no changes in stroke volume or cardiac output were observed. However, genes important in eye development and phototransduction were downregulated in oil-exposed larvae, with an increased occurrence of cellular apoptosis, reduced neuronal connection, and reduced optokinetic behavioral response in zebrafish larvae.