Clever Coral Trout Recruit Eels To Catch Elusive Prey


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Your average fish has probably never been thought of as the smartest of creatures, but new research from UK's Cambridge University suggests that underwater dwellers like the coral trout, could probably teach humans a thing or two about clever alliances and teamwork.

It has long been known that the trout, which dwells amidst the coral reefs in the Pacific and Indian Oceans is piscivorous - which means they devour other fish! Scientists were also aware that they hunted their prey using one of two strategies - prowling or ambush.

When prowling, the coral trout seek out schools of fish that are higher up in open water and follow them stealthily, until they get a chance to grab one. Though they have a high margin of success with this method, they prefer 'ambushing' their prey since all they have to do is lay on the ocean floor and wait for the 'food' to swim their way. The only drawback to this strategy is that while it works with larger fish, the smaller ones often escape by sliding into the network of underground nooks and crevices.

Turns out that the clever trout have managed to solve this problem, by forging a partnership with the eels that feed on the same prey. Initial observation of this collaboration was made a few years ago by Redouan Bshary of the University of Neuchatel and Alexander Vail of Cambridge University who observed the coral trout and its close relative coral grouper, reaching out to slippery moray eels for help in chasing out prey that was hiding inside the otherwise inaccessible seabed holes, in the Indian and Western Pacific oceans.

In order to investigate how this clever association worked, Vail and Bshary recently teamed up with Cambridge zoologist Andrea Manica, to conduct a controlled aquarium experiment involving the two ocean dwellers. They began by placing the coral trout in an aquarium that contained a plastic moray eel and a frozen baitfish. By controlling both with fishing lines, the researchers mimicked what would happen in a real-life hunt - Sometimes the baitfish would be within easy reach while at others, it would be hidden from sight. Initially, the coral trout sought out the eel's help indiscriminately. However, within a day, it seemed to realize that it was unnecessary, and became more selective.

For their second experiment the scientists placed two moray plastic eels - One was designed to obey the trout's request and "swim" forward when signaled. The other model refused to respond no matter how many signals it received from the trout. Once again, it took just a day for the clever fish to figure out who the better hunting partner was. From then on it chose to signal the "cooperative" eel five times out of six.

Even more interesting was that the fish - both in the wild and within the confines of the aquarium - were observed communicating with a surprisingly sophisticated array of gestures and signals. When approaching a moray eel in a crevice, a vigorous headshake meant "come hunt with me.", while a headstand was the fish's equivalent of pointing a finger to show the eel where prey was hiding. In response, the cooperative and equally clever eel would slide into the little crevices and begin its pursuit.

So why would these critters team up to land the fish a meal? Turns out that the eel is actually pursuing the fish for itself and is only looking to the trout for guidance about where to find it. In some cases it manages to snag it, whilst in others, the prey escape only to find a coral trout waiting. When these two hunters work together, the poor fish have no hope of surviving.

According to Vail, the partnership seems to equally benefit both teammates, with the predators catching roughly the same amount of fish. While the trout and eel are ultimately looking out for themselves, they have realized the power of working together as a team!

Prior to this, the only other non-human species known to exhibit this kind of advanced teamwork behavior is the chimpanzee. In fact, the coral trout performed just as well as chimps from a 2006 study when it came to team-based food gathering. Additionally, the use of referential gestures like pointing, had previously only been seen in highly intelligent animals like dogs, dolphins and apes. Vail, whose team published their findings in Current Biology on September 8th, suggests that this new discovery provides evidence that, "A big mammalian brain is not necessarily required to undertake these sophisticated forms of communication. This has led the team to conclude that "We are still a long way from a thorough understanding of fish brains and the mental computation they may be capable of."

This is not the first species to have surprised humans with their superior mental prowess. Caledonia crows have given a new meaning to the term "bird brain" with their sophisticated tool handling, whilst the Octopus have proved that they are not just an eight-legged tangled mess with their use of coconut shells as mobile homes and armor. Then there are the elephants that can do math and the ants that can sense earthquakes, and . . . the list goes on!,,,

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