Predator-Prey – Science Sushi

An electric eel strikes towards its prey. Photo by Ken Catania, Vanderbilt University — An electric eel reaches for its prey. Photo by Ken Catania, Vanderbilt University

Lurking in the muddy waters of the Amazon is a fish that has fascinated some of the greatest scientists in history, including Darwin and Faraday. The electric eel (Electrophorus electrics) is one of the most notorious species on the planet, and yet, there is still much to be learned about these elusive fish.

Despite the name, electric eels aren’t actually eels at all — they’re the only species in the genus Electrophorus, a member of the knifefishes (order Gymnotiformes). These slender shockers can grow to lengths in excess of 7 feet and weigh almost 50 pounds, and are one of the top predators in the muddy South American waters they call home. Their name comes from the current-producing cells that coat roughly two-thirds of their body, called electrocytes, which can collectively discharge more than five times the voltage of a US power socket.

In humans, the shock produced by electric eels feels much like that of a stun gun, causing brief, painful paralysis by overactivation of muscles. And since the discovery that these slippery fishes can cause such a strong electrical pulse, it has generally been assumed that they use their weaponized electricity to stun prey, using their electric organs to produce taser-like shocks. But neurobiologist Kenneth Catania wasn’t sure that was the whole story. While the eels’ shock is enough to take out the small goldfish fed to them in captivity, Catania wasn’t sure that it would work on the diversity of invertebrates and fishes that could comprise the eels’ natural diet. He was curious what would happen if the eel were presented with larger, less easily subdued meal choices. Continue reading “Electric Eels Shock Scientists With Sophisticated Hunting Strategies”

A dusky dottyback considers whether the damselfish in front will fit in its mouth. Photo by Christopher E. Mirbach — A dusky dottyback considers whether the damselfish will fit in its mouth. Photo by Christopher E. Mirbach

Life as a damselfish is hard. These small species are common on tropical reefs worldwide, eating tasty plankton and nipping at other fish. They’re known for their attitude and their beauty, and are often found in stunning schools that cluster around coral heads. But while they’re abundant and vibrant, what they lack are good defenses — no spines, no toxins. Indeed, they are the perfect morsel for other fish-eating fish, and they know it. The moment a predator is detected, they’ll dart for cover, their speed and agility their only hope of survival.

As perpetual menu items, damselfish have developed multiple mechanisms for detecting danger. They can even “smell” danger — when damselfish’s skin is injured, certain chemical compounds leech into the surrounding water. Other damsels can sense these chemicals — essentially “smelling” them — and when a damselfish catches a whiff of Eau de Injury, it runs and hides. But while these chemical alarms seem to benefit fellow damselfish, scientists have long debated whether the injured fish has anything to gain from sending out chemical cues. Are the compounds simply a byproduct of the physical damage? Or do they serve some greater purpose to the fish under attack?

Now, an international team of scientists have published the first evidence of an individual fish benefitting from releasing these chemical alarm cues in a new paper in Proceedings of the Royal Society B. Continue reading “Damsels In Distress Chemically Call For Help”