The induction of a radiation-induced bystander effect in fish transcends taxonomic group and trophic level

PURPOSE: To extend the investigations of bystander effect induction in fish of the same species as the irradiated fish, to bystander effect induction between fish species and between trophic levels. MATERIALS AND METHODS: To investigate interspecies bystander effect induction, zebrafish and medaka were irradiated with a 0.5 Gy X-ray dose and then swum with non-irradiated fish of the same and opposite species. To investigate trophic level bystander effect induction, California blackworms were irradiated with the same X-ray dose and then fed to non-irradiated rainbow trout. RESULTS: Reductions in clonogenic survival of the HPV-G (non-transformed human keratinocytes, immortalized with the human papilloma virus) reporter cell line, treated with tissue explant media, revealed that zebrafish and medaka induced a pro-apoptotic bystander effect in the other species and that, in trout, the normally anti-apoptotic effect caused by the consumption of non-irradiated blackworms was significantly reduced or lost if the blackworms had been irradiated. CONCLUSIONS: These results are the first to show that a radiation- induced bystander effect can transcend taxonomic group and trophic level in fish. This provides further evidence that bystander signals are widespread and conserved and may be transmitted through an ecosystem, as well as between individuals of the same species.