TEFLUTHRIN-INDUCED MASS MORTALITY OF FARMED RAINBOW TROUT (ONCORHYNCHUS MYKISS) IN SERBIA: A CASE STUDY

We present the first documented case of mass mortality in farmed rainbow trout (Oncorhynchus mykiss) linked to tefluthrin contamination in a freshwater stream. In June 2013, a twelve-day pollution event occurred in the Rogačica River, Republic of Serbia, resulting in the death of approximately 160,000 trout fingerlings and yearlings, with a total biomass of 4,190 kg. Water samples were analyzed for pesticide residues using liquid chromatography–tandem mass spectrometry (LC-MS/MS) with an Agilent 1260 Infinity LC system (Agilent Technologies, USA) coupled to a 6460 Triple Quad LC/MS mass spectrometer. Water analysis revealed tefluthrin concentrations of 2.04 and 0.52 μg/L, representing 9- to 34-fold exceedances of the reported 96 h LC50 for rainbow trout (0.06 μg/L). The contamination originated from washing pesticide-coated corn seed in a local distillery, representing a previously undocumented source of aquatic pesticide pollution. This case highlights the vulnerability of aquaculture to agricultural pesticides, the particular sensitivity of early life stages of salmonids to pyrethroids, and the need for improved regulatory and biosecurity measures to prevent similar events.