Aetokthonotoxin (AETX) is a formally undescribed neurotoxin produced by the cyanobacterium Aetokthonos hydrillicola (Ah). Animals that consume Ah-colonized vegetation may develop vacuolar myelinopathy (VM), a neurological condition causing motor impairment and death. We quantified AETX concentrations in the gastrointestinal tracts and fillets of secondary and tertiary consumer fishes from an Ah-inhabited reservoir. We also created a laboratory food chain involving Ah, an omnivorous fish, and a carnivorous fish to determine the trophic transferability of AETX in fishes. Finally, we used a swim chamber to quantify sublethal effects of AETX in fishes. Although AETX bioaccumulated in fishes, evidence of AETX biomagnification was not found. Fish did not develop VM, nor did AETX affect fish swimming performance. AETX accumulation in primary consumers should be quantified to determine the ecological risk of AETX in various food chains. Mammalian bioassays are also recommended to help determine the risk of AETX consumption in humans.