Copepods are largely used in toxicity tests. The nauplii of these organisms are more sensitive to contaminants than the adult stage. The aim of the present study was to test a protocol for the use of nauplii of the copepod Tisbe biminiensis in the ecotoxicological assessment of seawater. The sensitivity of these organisms to zinc sulphate (ZnSO4·7H2O) was also determined. The following conditions were established for the protocol based on the best development of nauplii to copepodites: 72-h duration, the microalga Chaetocerus gracilis at 2.5×105cellsmL−1 as feed and incubation temperature of 28°C. In the zinc sulphate sensitivity tests, EC50−72h and LC50/72h were 3.25±0.59mgL−1 and 3.46±0.72mgL−1, respectively, as estimated by the final number of copepodites and total number of live animals in relation to the mean number of inoculated nauplii. The estimated NOEC was 2.0mgL−1. The test developed is fast and not labour intensive. T. biminiensis nauplii exhibit sensitivity to zinc sulphate similar to that of other species of copepods employed in water toxicity tests, demonstrating the usefulness of these organisms in ecotoxicological studies involving samples of environmental seawater. •A practical toxicity test with Tisbe biminiensis nauplii to marine water was defined.•T. biminiensis nauplii sensitivity to zinc is similar to other copepod species.•The EC50−72h and LC50−72h of T. biminiensis nauplii to zinc were similar.