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(Intro)

Humans have been eating seafood for thousands of years, and in many ways, it's awesome.  Animals like fish don't produce as many greenhouse gases as say, cattle do, and also, they're just plain delicious.  Sorry, non-fish eaters.  Unfortunately, getting this kind of high quality protein isn't always easy.  Some animals don't grow fast enough to be a sustainable food source, and others taste pretty gross for at least part of the year, so to solve these problems, scientists have turned to a maybe unexpected field: genetics.

By carefully breeding or modifying aquatic animals, they've found ways to get us more efficient, responsible, and delicious meals, and if you're a seafood fan, the odds are good that you've encountered at least one of these three examples on your plate.  Our first example is catfish.  Every year, the world consumes hundreds of millions of kilograms of these fish, but the animals only grow so fast, so since the 1960s, the catfish industry has been collaborating with researchers to get those crispy fillets to our plates more sustainably.

One way they've been doing this is by cross-breeding species of catfish, trying to find a hybrid with the most commercially desirable traits and they found one.  It's a cross between a female channel catfish and a male blue catfish, and appropriately, it's called the channel-blue.  This hybrid is bigger and is better at converting food to body weight than either of its parent species.  It also has a higher survival rate and improved disease resistance.  

The verdict is still out on how and why this happens, but the hypothesis is that the channel-blue just ended up with a really useful combination of genes.  Unfortunately, though, you can't just throw channel and blue catfish in a pool and wait for them to produce tasty offspring.  These species rarely mate with each other in the wild.  To get a channel-blue, you have to do things like treat female channel catfish with hormones to induce ovulation, then mix in sperm from male blue catfish.

Don't get me wrong.  This method is effective.  In 2011, about 20%
 of the catfish harvested were channel blues, but it's not always successful, so the next step for researchers is to find a way to breed these species more efficiently.  Among other things, some scientists are trying to do this by mapping the genes of both parent species.  They're hoping to find genetic markers that could someday help channel and blue catfish mate more readily.  So maybe we'll be seeing more of these hybrids soon.  

Catfish isn't the only seafood we're interested in improving, though.  Another example is oysters.  Oysters aren't as widely consumed as catfish, but people do love slurping them down and the demand for them is growing.  The problem is wild oysters don't always contain a lot of good meat.  During spawning season, they're smaller with mushy, runny flesh and their gonads take up around 40% of their body mass.  For real.  Some could call them the ballsiest creatures on Earth.  That just doesn't sound appetizing.

So scientists found a workaround.  They made commercial oysters sterile.  They did it by engineering triploid oysters.  These are oysters with three sets of chromosomes, one more than normal.  This odd number messes with their ability to produce sperm and egg cells, which means the animals have more energy to devote to growing fatter and tastier.  

Scientists started experimenting with triploid oysters in the 1970s and 80s, but while they did achieve some victories, their methods weren't good enough to go widely commercial.  They were creating triploids by applying chemicals to recently fertilized eggs, and that wasn't always successful and didn't go over well with the public, so in 1993, scientists tried a modified approach.  First, they combed through the triploid oysters from previous experiments and found the rare exceptions that were somehow still fertile.

Then, they took the oysters' eggs and injected them with sperm cells containing one more set of chromosomes.  Ultimately, this led to the creation of a tetraploid oyster, one that had four sets of chromosome, and when that animal mated with a normal oyster with two sets of chromosomes, it produced sterile triploid offspring.  Today, this idea is what leads to those fat, juicy oysters you order at restaurants.  So not only is the food fancy, but the science is, too.

Now, as weird as they might be, neither hybrid catfish nor triploid oysters are considered genetically modified, because they weren't engineered by directly transferring specific, deliberately chosen genes.  This last example, though, is a proper GMO.  In fact, it's the first truly GMO animal to hit the market for human consumption.  It's called the AquAdvantage Salmon.  

Unlike wild oysters and catfish, wild Atlantic salmon are already pretty good at converting food into body mass, but scientists wanted to create an even more efficient version, because like, have you tasted salmon?  Don't you want more of that?  To modify this animal, researchers took fertilized eggs from wild Atlantic salmon and inserted two new components: the growth hormone gene from a Chinook salmon and a short bit of DNA called a promoter from a fish called an ocean pout.  

The Chinook gene was chosen because compared to Atlantic salmon, these salmon tend to grow more from the same amounts of food, and the ocean pout promoter was chosen because it allows the pout to grow year-round, as opposed to the Atlantic salmon, which only grows during certain times.  These researchers essentially took two beneficial traits and threw them into one organism.  

They also made the salmon triploid and sterile, to make sure they could never mate with wild salmon, even if they somehow escaped captivity.  The AquAdvantage fish was tested for safety and approved for sales in early 2019, and compared to its wild counterparts, it grows faster and reaches the same size with 25% less food, so more salmon for us.  

Projects like these are major ways we can continue eating seafood without taking as much of a toll on wild populations and habitats.  They won't solve all of our problems, but these clever, creative ideas do have the potential to really improve sustainability. 

If you want to learn more about how scientists are improving agriculture, you can check out the series Curious Minds: Global Food Supply over on CuriosityStream.  The five episode series talks about things like food security and the use of antibiotics in farming and it's really fascinating stuff.  It isn't the only series CuriosityStream offers either.  The subscription streaming service has more than 2400 documentaries and non-fiction titles from some of the best filmmakers in the world, and you can get unlimited access to them for just $2.99 per month.  If you want to check them out, your first 31 days of CuriosityStream are completely free if you sign up at curiositystream.com/scishow and use the promo code 'scishow'.  When you do, you'll be supporting us and helping us make more content like this, so thank you.

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