If you’re an eco-conscious eater, you’ve probably asked how your fish journeyed from ocean to aisle. But have you ever asked how the fish died? Researchers have shown that meat from stressfully slaughtered fish may have a shorter shelf life—and a worse taste—than fillets from quickly killed fish. In the study, to appear in the 1 January 2016 issue of Food Science, the team compared two groups of rainbow trout. Fish in the first group died from a swift strike to the head. In the second group, lingering asphyxiation above water—a common practice—killed them. After 75 days in the freezer, fatty acids like omega-3s—the heart-healthy chemicals that attract so many people to consume fish—started to break down in the fillets from stressed-out trout. When the researchers measured the breakdown products of fatty acids, they found twice as many in asphyxiated trout after 135 days in storage. To determine the potential impacts for fish aficionados, the scientists enlisted four judges specially trained in detecting “marine off-flavors” to taste test the samples. Fillets from the asphyxiated group tasted bitter and smelled rancid after 105 days, they reported, whereas fillets from the quickly killed fish never started to smell. The authors suggest a higher concentration of hydroperoxides—compounds that accrue in the body during stress—led to the quickened rancidness. Hydroperoxides break down into aldehydes and ketones: the chemicals behind the foul smell and bitter taste of unsavory meat. The results could encourage faster slaughter for more fish, whose expressionless faces tend to inspire less empathy than cows and pigs, the authors say.