They are tiny and cute and can be seen in countless aquariums. Surely the Guppy is at the bottom of the predator list. Maybe not. A new chemical study puts the guppy high up on the food chain. Even higher than a shark, according to Greg Michalski, an assistant professor at Purdue University. Is it time to fear the Guppie? Let’s look at what they found.
The study looked at atoms of nitrogen called nitrogen isotopes. The heavier version, nitrogen-15, accumulates farther up the food chain. So, plants have the lowest levels of heavy nitrogen, while a top predator, like a shark or a tiger, would have the highest.
Nitrogen-15 increases as it goes up the food chain because the animals excrete the lighter form, nitrogen-14, leaving the heavier version in the body. In the study, they found that filter-feeding animals, like clams, had low nitrogen-15 levels. Fish at the top of the food chain, like tuna and swordfish, had the most. The most interesting part of this study was what they found in the common guppy. Some of the highest levels of heavy nitrogen ever recorded. Surely that can’t be right. I’m far more worried about Sharks than Guppies.
There is a reason for this strange phenomenon though. Turns out that fish food is the reason. Fish flakes are produced by the leftovers from commercial fisheries: fish heads, guts, and fins. That’s where the heavy nitrogen comes from and where the Guppies get it.