Ecotoxicological effects of crude oil on Danio rerio early life stages: a molecular, morphological and behavioral approach focused on swim bladder development.

Proper development and inflation of the swim bladder is essential for swimming and foraging behavior in fish. To characterize the effects of the Brazilian oil spill that occurred between 2019 and 2020 to early life stage fish, the expression of genes involved in swim bladder development were targeted, with biochemical assays, morphology, and behavior assessed. The swim bladder was focused on due to recent findings of being a target of polycyclic aromatic hydrocarbons (PAHs) present in oil. Zebrafish (Danio rerio) were exposed to oil water accommodated fractions (WAFs) at concentrations measured following the spill, 1.12 to 71.8 total PAHs (μg-ΣPAHt L-1). Larvae exposed to 4.49 and 17.9 μg-ΣPAHt L-1 had a downregulation in the expression of swim bladder development genes, hb9, sox2, has2, and elovl1a, at 48 hours post fertilization (hpf). Downregulation in these genes was associated with a high frequency of uninflated swim bladders at 96 and 168 hpf, with uninflated swim bladders detected in 100% of 96 to 168 hpf larvae exposed to 35.9 and 71.8 μg-ΣPAHt L-1. SOD and CAT levels were inhibited in larvae exposed to 1.12 and 2.24 μg-ΣPAHt L-1, respectively. There was an increase in GST and GSH levels in exposed larvae. Average swimming speed and distance were reduced in larvae exposed to 1.12 μg-ΣPAHt L-1. This suggests that complex mixtures of PAHs from crude oil can inhibit the transcription of genes involved in swim bladder tissue development and proper swim-up behavior, which may have implications for the viability and success of developing larvae, impacting recruitment.