Toxicity of a commercial herbicide containing terbutryn and triasulfuron to seabream (Sparus aurata L.) larvae: a comparison with the Microtox test

The present study aimed to compare the sensitivity of larvae of the gilthead seabream (Sparus aurata), a valuable fish species of the Spanish South Atlantic littoral, with the extensively used Microtox test on a commercial herbicide formulation containing terbutryn (59.4%) and triasulfuron (0.6%). To this purpose, mortality displayed by endogenous feeding S. aurata larvae exposed during 72h post-hatching to nominal concentrations of the commercial formulation and bioluminescence of the marine bacterium Vibrio fischeri were compared. Histomorphological changes were also studied. Clearly, the S. aurata assay was the more sensitive indicator of toxicity for this herbicide. The 72-h concentration lethal to 50% of the individuals (LC50) found for yolk sac larvae was 1.41mg/L. This value was more than one order of magnitude below the 15-min EC50 found for V. fischeri (15.94mg/L). Growth of the larvae was not significantly affected by a terbutryn–triasulfuron mixture at concentrations up to 1.56mg/L, the maximum at which there was some proportion of survival.