If, on the other hand, you were thinking of the gigantic whale shark, the largest extant species of fish known, you are right.
Whale sharks ( Rhincodon typus ) are filter feeders and have long been observed eating krill on Western Australia’s Ningaloo Reef. However, while we have long known that they gorge on krill, new research has shown that they can also benefit from eating plant material.
a surprising discovery
The findings, published in the journal Ecology, confirm that the whale shark is the world’s largest omnivore. (Omnivores are animals—like humans and most bears—that eat and get nutrients from both meat and plants.)
The researchers analyzed biopsy samples from whale sharks on the Australian reef and found that the animals were actually eating a lot of plant material.
“This makes us rethink everything we thought we knew about what whale sharks eat,” fish biologist and lead author Mark Meekan said in a statement from the Australian Institute of Marine Science.
Analyzing food sources
Scientists carefully analyzed possible food sources, ranging from tiny plankton to large algae, looking for amino acids and fatty acids. They then looked at what was present in the skin samples from the whale sharks. The whale shark tissue contained compounds found in Sargassum, a type of seaweed common in Ningaloo, which breaks off the reef and floats to the surface.
“So the view we have of whale sharks coming to Ningaloo just to feast on these little krill is only half the story. In fact, they are also eating a good amount of algae”, the researchers expose.
Kodiak vs Whale Shark
Whale sharks have now risen to the top of the omnivore size chart, easily edging out other contenders such as Kodiak bears (weighing up to 1,500 pounds), as whale sharks can easily weigh 40,000 pounds.
“In the sea, we always thought that animals that had gotten really big, like whales and whale sharks, fed one step up the food chain with shrimp-like animals and small fish. It turns out that perhaps the system of evolution on land and in water is not so different after all ,” the authors say in their study published in the journal Ecology.
“Something like a whale shark, which swims through the water with its mouth open, is going to ingest a lot of different things. But you don’t know how much of that has been used by the animal and how much of it comes right out the other end. Whereas stable isotopes, because they’re actually built into the body, are a much better reflection of what animals actually use to grow,” concluded Andy Revill, a biogeochemist at CSIRO. ).
Referencia: M.G. Meekan et al. The world’s largest omnivore is a fish. Ecology, published online July 19, 2022; doi: 10.1002/ecy.3818
