Toxicological Effects of Diuron Exposure on Javanese Medaka (Oryzias javanicus): Insights from a Tropical Estuarine Fish Model

Abstract

Diuron, a biocide widely used in agriculture and offshore industries, can cause acute toxicity in aquatic organisms, leading to fatal outcomes and behavioural disruptions. This study assessed its toxic effects on Javanese medaka (Oryzias javanicus) to determine safe exposure levels and support guideline development for Malaysian river and coastal waters. Eight triplicate treatments were prepared, each with 10 individuals (mean size 3.0 ± 0.3 cm, n = 240) exposed to 1.0 to 20.0 mg/L concentrations. Acute toxicity was evaluated over 96 hours using probit analysis to calculate the median lethal concentration (LC₅₀), which was found to be 5.90 mg/L. No mortality occurred in the control groups. Behavioural endpoints—including surfacing, burst swimming, loss of coordination, and pigmentation changes—were significantly observed in the exposed groups, with noticeable responses beginning at 5.0 mg/L compared to the control. The results highlight the high sensitivity of O. javanicus to this herbicide, supporting its suitability as a bioindicator species for aquatic toxicants. Due to its ecological adaptability and sensitivity, Javanese medaka is a valuable tropical model for ecotoxicological research in Malaysia.