Ring test of an embryo‐larval toxicity test with zebrafish (brachydanio rerio) using chromium and zinc as toxicants

A protocol for determination of “no‐effect” concentrations on hatch and survival in the zebrafish ( Brachydanio rerio ) has been evaluated at five laboratories for variability using chromium (K 2 Cr 2 O 7 ) and zinc (ZnSO 4 × 7H 2 O) as toxicants. Repeatability ( r ) and reproducibility ( R ), expressed as C.V. (coefficient of variation), for logarithmic median survival time ranged between 1% and 9% for r and between 1% and 29% for R depending upon concentration of toxicant. Variability increased at high concentrations, especially for zinc. For logarithmic median hatching time, C.V. for r ranged from 6% to 24% and for R between 11% and 27% for the various concentrations of chromium and zinc. Estimated logarithmic “no‐effect” concentrations on survival of zinc and chromium had a C.V. for r below 10% and a C.V. for R below 15% for zinc and below 25% for chromium. Zinc delayed the time to hatch at lower concentrations than those that reduced survival time, for the estimated logarithmic “no‐effect” concentrations of zinc on hatch r was around 75% and R around 100%. The “no‐effect” concentrations based on all nine or ten tests from the five laboratories were 15 mg Cr/L and 0.5 mg Zn/L. Because of the cumulative toxicity of chromium in fish the chronic “safe” concentration may be considerably lower, but the “no‐effect” concentration of 0.5 mg Zn/L for effects on hatching time is consistent with the chronic “safe” concentration found in other species of fish at the same hardness (100 mg/L expressed as CaCO 3 ).