In any serious philosophical debate about the plusses and minuses of death, someone has to reference Epicurus' letter to Menoeceus about death being "nothing to us." Epicurus' point was that if death destroys our ability to experience anything, we obviously can't experience the state of being dead, and how can something that we don't experience hurt us? This was supposed to ease anxiety about our own inevitable collapses into dust, but it has an odd side effect: It implies that there's nothing bad about dying prematurely or being killed. Yes, dying unexpectedly could prevent us from finding out how Scandal ends, or how Hannibal ends, or how Downton Abbey ends, or from spending more time with the people we love and so on, but the beauty of death is that you also won't care about any of that because there won't be a you to do the caring.
Because this sounds weird and not right to a lot of people, death-averse philosophers devised a "deprivation account of the harm of death." This refers to any convoluted philosophical explanation for why a premature death is in fact bad by slamming the door on all future experiences. "Death is every bit as horrible as it seems" may not be as reassuring as Epicurus' shrugging off of mortality, but it does at least fit the mainstream intuition of "try not to die, because when you're dead you're missing out."
It's not really murder if it's just a slightly earlier death than nature intended, right?
The people who really hate death, let's say pro-life pacifist vegans, obviously tend to side with the deprivation account of the harm of death. You'll especially see this with vegans when they talk about slaughter. (As a former vegan, I know this firsthand.) No conversation about knocking cows insensible, slicing their throats, and hanging them upside down until they are hollowed of their life fluids is complete without a reference to the 20-year-or-so potential lifespan that farmed cows almost never reach because most of them are killed before they're 5. This deprives cows of at least 15 years that they could have spent eating grass, relaxing, mooing, and hanging out with family and friends—seemingly a greater loss than if the maximum cow lifespan were exactly five years and they were invariably sent to slaughter mere hours before they would have died naturally anyway.
In his essay "Eating Animals the Nice Way" (2008), vegetarian philosopher and ethicist of killing Jeff McMahan says he could accept the consumption of farmed animals who were genetically modified to painlessly die at whatever age is convenient for us. He claims this genetically programmed death would not be premature or unjust since it would be inextricably woven into their very existences.
That is such a deprivation account of the harm of death's way of looking at it! Because these genetically modified self-destructing farm animals don't yet exist and some people want to eat meat now, it's tempting for meat-eaters to respond, "Well look, the only reason we breed farm animals is to milk them, kill them, and eat them, so even without warping their DNA to shorten their lifespans, their dying in youth is an unalterable fact of their existences, so we're not depriving them of any future life when we slaughter them." But the truth is that farm animals dying young and leaving a good tasting corpse is more of a strong expectation than an unalterable fact. There is, for instance, Cinders the pig, whose life was spared because her fear of mud meant she had to wear miniature rain boots every day, which ultimately made her too adorable to kill. And then there are all the animals who have escaped the farming system to live relatively long, lazy lives on sanctuaries. They were all born to be food, but death by slaughter was not an inevitable fact of their lives either. This is the case for just about every animal we breed into being for our own selfish ends: Even if our plan always was to kill them, it's still technically possible for them to live longer.
Farm animals dying young and leaving a good tasting corpse is more of a strong expectation than an unalterable fact.
This should be worrying to any meat-eater who accepts the deprivation account of the harm of death, but the good news is that veganism is not the only answer. We haven't genetically engineered animals to happily die of natural causes when they are at their peak of deliciousness and economic sustainability (yet!). But we can approach that ideal now by targeting animals who are doomed from the start with naturally skimpy maximum lifespans. It's not really murder if it's just a slightly earlier death than nature intended, right? This rationalization won't please those who believe that it's almost always unnecessary and cruel to intentionally kill animals for food. But if you're an incorrigible meat-eater who rejects Epicurus' lackadaisical view of the end, the best way to honor your values is to take the lives of animals who never had much time to begin with.
The Seafood Watch Buyer's Guide, which alerts fish eaters to the most sustainable and ecologically harvested fish populations, might serve as an inspiration and template for the pescatarian version of this. I'd call it "The Seafood Buyer's Guide for Those Who Accept the Deprivation Account of the Harm of Death," organizing seafood choices according to the maximum potential lifespan of human-edible sea citizens.
The "Best Choices" would be those born on the cusp of death by natural causes, including many shrimp, smelt, and many species of squid, as well as the seven-figure pygmy goby, which enjoys a maximum of 59 days on this planet. As for larger fish, most tuna—with the exception of the longer-lived Pacific bluefin— also falls under this category, with lifespans ranging from five to 12 years. "Good Alternatives" are species in the medium lifespan range, living anywhere from 14 to 29 years. Here you've got catfish (15-25 years), cobia (15 years), blue marlin (18-27 years), swordfish (15 years), tilapia (20 years), and the ever-sustainable snow crab (14 years). Although few do, oysters can reach 20 years of age.
Eating a Turritopsis dohrnii jellyfish means depriving a creature of a potential eternity of life. Please refrain from eating immortal sea creatures.
The seafood to "Avoid" almost certainly had long and interesting lives ahead of them until you came trawling along. Eels can live up to 150 years and geoducks, delicious as they may be stir-fried or sautéed, happily reach their 160s. The Antarctic sponge—if you happen to have the wherewithal to find one in the first place—has an estimated lifespan of 1,550 years on the sub-freezing sea floor. The highly endangered sea turtle, meanwhile, tops out at a comparatively young 80.
Then there's the "Most Definitely Avoids," which includes one sea creature that is the worst possible choice for those who adhere to a deprivation account of the harm of death: the notoriously immortal Turritopsis dohrnii jellyfish. Jellyfish are generally an excellent choice, as many of them have lifespans as short as a few hours to a few months, but eating a Turritopsis dohrnii jellyfish means depriving a creature of a potential eternity of life. Please refrain from eating immortal sea creatures.
Of course, precise lifespan is difficult to estimate and often has to be revised upwards. Beyond that, knowing the lifespan of a species of animal doesn't tell us how much time an individual in that species has left. Killing a sea turtle who is 79 years and 364 days old would foreclose less potential future experience than killing a one-year-old anchovy. It would be nice if we could single out sea creatures by actual age, but for now the best we can do is imperfectly approximate by species. Maybe fishing tech will get there one day and allow us to pick animals right before they expire, giving them their maximum potential for life in the water and a glorious afterlife on the plate.