Microbial pathogens in recirculating aquaculture and egg incubation systems can cause elevated mortality and decreased production. Peracetic acid (PAA) is an effective disinfectant; however, its toxicity to early life stages of Atlantic salmon (Salmo salar) has not been assessed. This research determined the 24-hour LC50 value of PAA for three early life stages of Atlantic salmon: eyed eggs, fry, and fingerlings. Toxicity Relationship Analysis Program (TRAP) LC50 values for eggs treated for 5 and 10 minutes were 781.5 mg/L and 485.0 mg/L PAA, respectively. Trimmed Spearman Karber (TSK) LC50 values for eggs treated for 5 and 10 minutes were 771.1 mg/L and 462.1 mg/L PAA, respectively. TRAP LC50 values for fry and fingerlings were 4.0 mg/L and 5.3 mg/L PAA, respectively. TSK LC50 values for fry and fingerling were 4.1 mg/L and 5.3 mg/L PAA, respectively. These LC50 values provide guidance for developing safe PAA treatment protocols for Atlantic salmon eggs, fry, and/or fingerlings. 4 ACKNOWLEDGEMENTS This thesis is dedicated to my wife, Jordan Redman, who has supported me and encouraged me throughout my time as a graduate student. Thank you for dealing with my temper tantrums and rolling your eyes every time I claimed I would fail a class. I'd also like to thank my children, Casper and Coven, for providing reassurance during my moments of doubt. I hope your tails wag a little faster knowing that now both of your moms have Master's degrees! To my parents, I hope this makes me your favorite child, at least for a little bit. Lastly, I would like to rub this feat of intellect into the faces of my three older brothers. Many thanks to my thesis committee, Chris Good, Dave Straus, and Eric Annis. Words cannot express how grateful I am for your continued support and countless revisions! Special thanks are extended to