Salmo trutta is more sensitive than Oncorhynchus mykiss to early-life stage exposure to retene.

Salmonids are known to be among the most sensitive fish to dioxin-like compounds (DLCs), but very little is known about the sensitivity of the brown trout (Salmo trutta), which has declined and is endangered in several countries of Europe and Western Asia. We investigated the sensitivity of brown trout larvae to a widespread dioxin-like PAH, retene (3.2 to 320 μg.L), compared to the larvae of a salmonid commonly used in toxicology studies, the rainbow trout (Oncorhynchus mykiss). Mortality, growth, cyp1a induction and the occurrence of deformities were measured after 15 days of exposure. Brown trout larvae showed a significantly higher mortality at 320 μg.L compared to rainbow trout larvae. While the occurrence of deformities was only significantly increased at 320 μg.L for the rainbow trout, brown trout larvae displayed pericardial edemas and hemorrhages already at 10 or 100 μg.L. cyp1a induction was increased significantly already at ≥3.2 μg.L for the brown trout, versus ≥32 μg.L for the rainbow trout. Least square regression analysis of the concentration-response relationships suggested that S. trutta larvae were at least 2 times more sensitive than O. mykiss larvae for cyp1a induction. The present study suggests that S. trutta larvae are more sensitive than O. mykiss larvae to a potent DLC, retene. As it is possible that S. trutta populations have declined partly because of pollution by DLCs, we recommend generating more data regarding the sensitivity of threatened fish populations, in order to ensure better risk assessment.