Bacterial gill disease (BGD), caused by Flavobacterium branchiophilum and other species of yellow‐pigmented, filamentous bacteria, is a common and potentially catastrophic disease of hatchery (freshwater)‐reared fish. Chloramine‐T (Chl‐T) is a biocide proven effective for controlling mortality in freshwater‐reared fish diagnosed with BGD. However, Chl‐T is not approved by the U.S. Food and Drug Administration for such use. To generate data in support of a U.S. approval, we evaluated the effectiveness of Chl‐T (administered at 12 mg/L of static bath water for 60 min/d on three alternate days) to control mortality caused by BGD in freshwater‐reared chum salmon Oncorhynchus keta, Apache trout O. gilae apache, and rainbow trout O. mykiss. For each species, the mean percent total mortality in Chl‐T‐treated tanks (N = 3) was significantly less than that in control tanks (N = 3): Chum salmon = 8.9% versus 99.7%, Apache trout = 39.2% versus 97.9%, and rainbow trout = 5.7% versus 25.8%. Because the Chl‐T treatment regimen was efficacious for each species, we conclude that our findings support the approval of Chl‐T for use in the USA to control mortality in freshwater‐reared salmonids diagnosed with BGD.