Embryonic exposure to cadmium (II) and chromium (VI) induce behavioral alterations, oxidative stress and immunotoxicity in zebrafish (Danio rerio)

• Effects of Cd and Cr on the different endpoints in early life stage of zebrafish are evaluated.
• Cd and Cr influence free swimming activities and the swimming behaviors of larval zebrafish.
• Cd and Cr exposures induce oxidative stress of the larval zebrafish.
• Cd and Cr increase the mRNA levels of genes related to the innate immune system in zebrafish larvae.

Cadmium (Cd) and chromium (Cr) are considered as the main environmental contaminants which have serious risks for health. Firstly, we observed that the hatchability was significantly decreased by exposure to 10 μM Cd for 60 and 96 h post fertilization (hpf). And some abnormalities in embryos and larvae were observed especially in the 10 μM Cd treated group. Moreover, the free swimming activities and the swimming behaviors of the larval zebrafish in response to the stimulation of light-to-dark photoperiod transition were significantly influenced by both Cd and Cr treatments. Secondly, Cd and Cr exposure induced the changes in oxidative stress of the larval zebrafish. The malondialdehyde (MDA) levels increased and the glutathione (GSH) contents decreased significantly after the exposure to Cd or Cr for 96 hpf. Cd or Cr affected not only the activities of superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione S-transferase (GST), but also the transcriptional levels of their respective genes. Thirdly, with regard to the immune response, the mRNA levels of the main cytokines including tumor necrosis factor α (TNFα), interleukin-6 (IL-6) and interleukin-1 β (IL-1β) in the larvae increased significantly after the exposure to Cd and Cr for 96 hpf. Our results suggested that Cd and Cr have the potential to cause behavior alterations, oxidative stress and immunotoxicity in the larval zebrafish.