In Vitro Predictions of Acute Fish Toxicity for Development of Sustainable Crop Protection Products

New agrochemicals must demonstrate safety to numerous ecological systems, including aquatic systems, and aquatic vertebrate toxicity is typically evaluated by using the in vivo acute fish toxicity (AFT) test. Here, we investigated two alternative in vitro assays using a cell line isolated from rainbow trout (Onchorhynchus mykiss) gill tissue: (i) adenosine triphosphate (ATP) luminescence and (ii) cell painting. The former assay measures cytotoxicity, while the latter measures changes in cellular morphology in response to chemical exposure. We assessed how well end points in these two assays predicted acute lethality (i.e., LC₅₀ values) in independent in vivo AFT tests. When compared to results from OECD TG 249 (in vitro), we found that the ATP assay was not as predictive (R² = 0.53) as the cell painting assay. Similarly, when compared to results from OECD TG 203 (in vivo), the cell painting was much more predictive (R² = 0.67). Our results show that such in vitro assays are useful for fast and efficient screening alternatives to in vivo fish testing that can aid in the agrochemical discovery phase, where thousands of potential new actives are tested each year.