Lookin’ Like a Snack: An Aquaculture Story

Image from the Monterey Bay Aquarium

Veggie-loving Fish Could Be the New White Meat

It should be no surprise in 2020 to hear (again) that a vegetarian diet is the environmentally preferable alternative to one heavy in meat and other animal products. There’s all kinds of data showing how much more fresh water livestock consume as well as their outsize impact on greenhouse gas emissions when compared food crops. So as individuals and a global society, our eating habits have clear negative consequences. What might be less obvious, is that it’s not just human diets we need to worry about. Three billion people rely on seafood for their primary source of protein, and a growing percentage of that is coming from aquaculture as opposed to wild caught seafood.

While some view aquaculture as a much more sustainable or environmental alternative to wild caught seafood, it is not without its own issues. The majority of aquaculture operations are actually quite different from land-based livestock rearing in one key area: on land we raise herbivores, but in aquaculture we raise carnivores. Going the extra step, or sometimes multiple steps, up the food chain has a real cost. On average, only 10% of the energy an animal gets from whatever it eats is available for the next thing that eats it. And the problem compounds. A cow is only one step removed from the plant-based feed at the bottom level, but a salmon may be three, four, or even more steps removed from the algae at the bottom of the ocean food chain. In order to raise the fish destined for your plate, many more fish must be wild caught to be used as feed. Now, there are a few vegetarian aquaculture species – tilapia is the first to come to mind, plus shellfish like oysters – but those are not necessarily the most desirous (or delicious) for a dinner plate. We’ve landed in a pickle.

Or, should I say, a prickle. Prickleback, that is, and specifically a monkeyface prickleback (Cebidichthys violaceus). That is the colorful name for the large, eel-like fish native to US West coast tide pools. The prickleback is kinda funky, but important because it is one of those rare vegetarian fish – an adult eats only the algae growing in its tide pool. Scientists decided the prickleback was the perfect study subject to answer how fish meet their nutritional needs on a vegetarian diet, genetically speaking. They sequenced the prickleback genome, specifically the areas involved in the gut and digestion, looking for clues. They found that the monkeyface prickleback has specialized to be particularly good at digesting starch – not surprising given that’s the primary component of algae – but also has adapted to excel at extracting lipids from its food. Lipids (fats) are essential, but scarce in plants, so it actually makes sense for the prickleback to prioritize their capture. Understanding what these adaptations look like in the genetic code is crucial for identifying new species that might thrive on a vegetarian diet, or for creating just such a species through genetic manipulation. Turning aquaculture green in this way would solve one of its major challenges and, of course, be hella rad.

Johnny Venger‘s favorite meat is can-raised Spam.

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