When it comes to intelligence, fish tend to get a bad rap. While much discussion revolves around birds and mammals, fish have remained synonymous with a poor memory and stupidity. But the astonishing underwater tour that the BBC’s Blue Planet II is taking us on has revealed some incredibly complex fish behavior, including a fish that teams up with an octopus to get itself a meal.

“What we discovered is that this fish is capable of forward planning and co-operatively hunting with a completely unrelated animal, in this case, an octopus,” explained Jonathan Smith, who produced the "Coral Reefs" episode.

When the coral grouper finds a particular patch of coral rich in smaller fish hiding within, but out of reach of the fish itself, it will look for an octopus to pair up with. Incredibly, the two separate species have learned how to communicate with each other. The grouper indicates to the octopus by doing a headstand above the patch of coral where the little fish are hidden, it then flashes white and does a bit of a wriggle to get the cephalopod's attention.

“Then they both come over to where the fish is hiding and if the octopus wants to play, it can use its tentacles to get in and actually flush the fish out,” continued Smith. “Once it’s out in the open the coral grouper gets the fish about half the time, and about half the time the octopus snags it.”

This behavior, along with other standout footage from Blue Planet II such as the giant trevallies leaping from the water to catch flying birds, is changing many people's idea of what fish are capable of, and just how intelligent they actually are.

Dr Alex Vail, one of the cameramen who helped film the grouper-octopus alliance, actually started off researching the cross-species cooperation out on the reef between the fish and other underwater predators. His previous work has shown that groupers are “as good as chimpanzees” in selecting the best partner for the task in finding food, consistently choosing the right moray eel that will help them out. Not only that but the fish also learn rapidly which eels are best up to the task.

But even Dr Vail was impressed with the fish teaming up with their multi-armed accomplices. “When I first saw it, I was blown away,” he told The Telegraph. “What's fascinating is there seems to be intention behind it. The grouper has formulated a plan and is aware of what the outcome might be, and then carries it out. Which shows a similar level of intelligence as chimpanzees. And that's without anything like the same brainpower.”

So next time someone says you have the memory of a goldfish, maybe you should take it as a compliment.