Hepatic proteome and toxic response of early-life stage rainbow trout (Oncorhynchus mykiss) to the aquatic herbicide, Reward®

The objective of this study was to examine the acute toxicity and sub-lethal effects of the commercial formulation of diquat dibromide, Reward® Landscape and Aquatic Herbicide, on multiple early-life stages of rainbow trout exposed to environmentally relevant concentrations. The continuous exposure 96 h LC50 derived for juvenile feeding fry aged 85 d post-hatch was 9.8 mg/L. Rainbow trout eyed embryos and juvenile feeding fry were also exposed to concentrations of Reward® ranging from 0.12 to 10 mg/L during two 24 h pulse exposures separated by 14 d of rearing in fresh water to mimic the manufacturers instructions for direct applications to water bodies. Effects on growth and development were evident at 9.25 mg/L during the embryo/alevin exposures, but not in feeding juveniles, indicating a higher sensitivity of the early life stage fish. Quantitative proteomic assessment and subnetwork enrichment analyses were conducted on hepatic proteins for both life stages to evaluate protein expression changes after 0.37 mg/L diquat via Reward® exposure. Unique cellular process expression profiles for pre-feeding swim-up fry and for feeding juvenile fish were observed, reflecting differences between the two life stages in sub-cellular responses after diquat dibromide exposure. Hepatic proteome effects were more dramatic in the pre-feeding swim-up fry with 315 proteins significantly different between the control and fish exposed to Reward®, while in the later life stage feeding fry, only 84 proteins were significantly different after Reward® exposure. This study is the first to report the sub-cellular and whole organism level effects of diquat dibromide in a commercial formulation and demonstrates that numerous changes at the protein level occur at environmentally relevant concentrations based on aquatic application rates.