Data and Code release to accompany a USGS publication. Bayluscide, the 2-aminoethanol salt of niclosamide (2′, 5-dichloro-4′-nitrosalicylanilide), is a pesticide that is used in conjunction with TFM (4-Nitro-3-(trifluoromethyl)phenol) to treat streams tributary to the Great Lakes that are infested with invasive parasitic sea lamprey (Petromyzon marinus). The application TFM with 0.5 to 2.0 percent (%) Bayluscide can significantly reduce the amount of TFM required to achieve effective control. The current formulation of Bayluscide used in combination TFM during stream treatments conducted the Great Lakes Fishery Commission binational Sea Lamprey Control Program is an emulsifiable concentrate (EC). The Bayluscide EC formulation is highly effective; however, it degrades application tubing, causes difficulty for application equipment cleaning, and, more recently, raises concerns for worker safety because of the carrier solvent. We collaborated with a contract formulation company to develop a Bayluscide 20% Suspension Concentrate (SC) formulation as a potential replacement for the Bayluscide 20% EC formulation. The Bayluscide 20% SC formulation was specifically developed using inert ingredients known to and approved for use by the United States Environmental Protection Agency and Health Canada Pest Management Regulatory Agency. However, inclusion of a small quantity of an antimicrobial in the formulation warranted evaluating the toxicological profile to sea lamprey and select nontarget fish species. We evaluated and compared the toxicity of the Bayluscide 20% SC formulation to the Bayluscide 20% EC using a continuous flow diluter system and larval sea lamprey and select cold, cool, and warmwater fish as test animals. Our results demonstrate comparable toxicological profiles between the two formulations with the Bayluscide 20% SC formulation being slightly less toxic to nontarget fish. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.