A previous investigation (McDonald et al., 2021) into uptake of metals by the benthic estuarine fish, the blue-spot goby Pseudogobius sp. (Perciformes: Gobiidae) resulted in no detectable uptake of dissolved cadmium (Cd) or zinc (Zn) radiotracers after 60 hours exposure. Radiation counts in live animals were consistently below detection limits, even when exposure was at high total metal concentrations (3.5 and 1,240 µg/L for Cd and Zn respectively). Based on the analysis of exposure water radioactivity, lack of sorption of metals to exposure containers, and regular confirmation of detector instrumentation, we confidently concluded that the lack of aqueous uptake was genuine. A complementary set of experiments were undertaken at the International Atomic Energy Agency (IAEA) radioecology laboratories with a similar benthic estuarine/marine fish, the sand goby Pomatoschistus minutus (Perciformes: Gobiidae), which also resulted in no detectable uptake of Cd and Zn after 2.5 days exposure. This paper describes the methods and results of the two studies and provides a discussion on the potential explanations for no bioaccumulation of aqueous Cd and Zn as well as the importance of reporting non-significant results in ecotoxicology.