What Is the Smartest Animal in the Ocean? Octopus, Dolphin and Orca Compared
No study tests whales, dolphins, octopuses and fish on the same task. Each famous result rests on very few animals: 2 dolphins in a mirror study, 1 orca copying sounds, 4 marked fish. By cortex neurons, the pilot whale leads with 37.2 billion.
What you need to know
- No one can name the smartest animal in the ocean, because no study gives whales, dolphins, octopuses and fish the same task. Each skill below was tested in a different species, and often in one to four animals.
- The samples are tiny: 2 bottlenose dolphins in the mirror study (Reiss and Marino, PNAS, 2001), one killer whale copying human and whale sounds (Abramson and colleagues, 2018) and 4 throat-marked cleaner wrasse, 3 of which scraped the mark in front of a mirror (Kohda and colleagues, PLOS Biology, 2019).
- By cortex neurons, the long-finned pilot whale leads: about 37.2 billion in the neocortex, almost twice the human figure in the authors' words, from 10 whales (Mortensen and colleagues, 2014). The count is a measure of size, not a test.
- Among animals without a backbone, octopuses learn by watching another octopus (Fiorito and Scotto, Science, 1992) and cuttlefish held out for 50 to 130 seconds for a better reward (Schnell and colleagues, 2021). No firm octopus neuron count exists.
No one can name the smartest animal in the ocean, because no study tests whales, dolphins, octopuses and fish on the same task. The best-supported candidates are the bottlenose dolphin, the orca and the octopus, each tested on a different skill, often on one to four animals. By brain cells, the long-finned pilot whale leads, with about 37.2 billion neurons in its neocortex, almost twice the human figure.
The new finding is the sample size behind each famous result. Two dolphins, one orca and four marked fish carry some of the biggest headlines. Below: one comparison of what each ocean species was tested on, what the catch is, and why the smartest sea animals cannot be ranked on a single list.
What is the smartest animal in the ocean?
The evidence does not name one. It names several animals that are very good at different things, so the honest answer is a comparison. Here is what each species was tested on, in the original papers, and the catch behind it.
- Bottlenose dolphin, mirror: Reiss and Marino (PNAS, 2001) exposed 2 dolphins to reflective surfaces. Both used the mirror to inspect marked parts of the body. Catch: only 2 animals
- Bottlenose dolphin, names: King and Janik (PNAS, 2013) found that wild bottlenose dolphins called back when they heard a copy of their own signature whistle, and not when they heard other whistles. Catch: it shows a response to a label, not what the dolphin understands by it
- Orca, imitation: Abramson and colleagues (Proceedings of the Royal Society B, 2018) tested one killer whale in a do-as-I-do task. It copied every familiar and novel whale and human sound tested, most within the first 10 trials and three on the first attempt. Catch: one animal
- Octopus, learning by watching: Fiorito and Scotto (Science, 1992) let untrained Octopus vulgaris watch trained octopuses pick one of two objects. The watchers then picked the same object, faster than the trained ones had learned. Catch: one species, one colour task
- Cuttlefish, self-control: Schnell and colleagues (Proceedings of the Royal Society B, 2021) found that cuttlefish held out for up to 50 to 130 seconds for a better food reward, and the ones that waited longer learned a reversal task better. Catch: a lab task, not the open sea
- Cleaner wrasse, mirror: Kohda and colleagues (PLOS Biology, 2019) marked 4 fish under the throat. In front of a mirror, 3 of the 4 scraped the throat, and none did so in the control periods. Catch: 4 fish, and the journal says reviewers disagreed
Read down the list and note the pattern. Every result is a strong finding about one species on one task. None of them puts the species on a scale with the others. Our smartest animals study shows the same thing across 222 species: the top animal changes with the measure.
Which is the smartest marine animal by brain size?
By neocortex neurons, the long-finned pilot whale. Mortensen and colleagues (Frontiers in Neuroanatomy, 2014) counted about 37.2 billion neurons in the pilot whale neocortex, almost twice as many as in humans, from the brains of 10 whales. Cetacean brains are the largest in the animal kingdom, the authors note.
They also warn what the count does not show. The whale's neuron density is lower than ours, so the high total comes from a bigger brain. They conclude that the number of cortical neurons does not by itself explain human cognition. A count tells you the size of the machine, not how it is used. Our guide to brain size and IQ makes the same point for people.
Is the dolphin the smartest sea animal?
Dolphins have the most varied evidence of any sea animal here, but a varied record is not a ranking. They use mirrors to inspect marked body parts, and wild bottlenose dolphins answer a copy of their own signature whistle. Our guides to dolphin IQ and orca IQ go through each species in more detail.
The orca result is the same kind of evidence. One whale copied sounds it had never produced, which supports the idea that the vocal dialects of wild orcas are learned. It does not show that orcas are smarter than dolphins, because the two have not been tested on the same task.
Ask which sea animal is smartest and the studies give a short list, not a winner.
Which is the smartest sea creature without a backbone?
The octopus is the best-known candidate for the smartest sea creature without a backbone, and its relative the cuttlefish has striking results too. The octopus learned by watching others in the Fiorito and Scotto study. Finn, Tregenza and Norman (Current Biology, 2009) reported coconut-shell carrying by an octopus under the title Defensive tool use in a coconut-carrying octopus, though we could not read the full letter.
There is no firm neuron count to compare. Our smartest animals study left the octopus out, because the classic count could not be checked and later summaries quote totals from about 30 million to 500 million. Our octopus IQ guide covers the species in detail, and the smartest insect article covers another group of small-bodied animals with surprising skills.
Can a fish be among the smartest animals in the ocean?
A fish can pass a modified mirror test, which is surprising. In the Kohda study, 3 of 4 throat-marked cleaner wrasse scraped the mark in front of a mirror but not in the control conditions. The authors then ask whether this shows self-recognition or something else, and the journal published a companion piece with another view.
That is a good reason to be careful with the mark test as a measure of intelligence. If a fish passes, either fish are self-aware or the test measures less than we thought. Either way, a small result from 4 fish is a question to follow up, not a place in a ranking.
How should you read a result from one ocean animal?
Start with how many animals were tested. A result from 2 dolphins or one orca can be real and still say little about all dolphins or orcas. Then ask whether the task suits the body. A mirror test needs good eyesight and a way to touch a mark, which is why the wrasse study had to change the test.
Last, ask what was learned and what was natural. A lab animal copying human sounds shows what the species can do, while wild dialects show what it does. The two support each other here, but they are different kinds of evidence. A ranking needs all of them for every species, and none exists yet.
Why can't ocean animals be ranked by IQ?
An IQ is a position on a bell curve built from thousands of people, with a mean of 100 and a standard deviation of 15 on most modern tests. No norm group exists for any sea animal. The IQ bell curve shows what the number means for people. Researchers compare animals one skill at a time, and the smartest marine animal depends on which skill you pick.
Where would your own score land?
Ocean animals have no IQ, but you can have yours measured. The IQ Metrics test reports a score on the standard scale with its percentile.
Find your IQ score now! →If you want a number for yourself, take the IQ test and read it against the bell curve. Animals have to be compared task by task, while people can be placed on one scale. Our earlier article on the smartest bird in the world does the same comparison for birds.
Common questions
What is the smartest animal in the ocean?
No one can say. No study tests whales, dolphins, octopuses and fish on the same task. Bottlenose dolphins, orcas and octopuses have the strongest evidence, each on a different skill and often from one to four animals. By neocortex neurons the long-finned pilot whale leads, with about 37.2 billion.
What is the smartest sea creature without a backbone?
The octopus is the best-known candidate. In a 1992 Science study, untrained Octopus vulgaris that watched trained octopuses pick the same object. Cuttlefish held out 50 to 130 seconds for a better reward in a 2021 study. No firm neuron count exists for the octopus.
Is the dolphin smarter than the octopus?
The studies cannot say, because the two have not been tested on the same task. Two bottlenose dolphins used a mirror to inspect marked body parts. Octopuses learned a choice by watching another octopus. Each is a strong result on a different skill.
Which marine animal has the biggest brain?
Cetaceans have the largest brains in the animal kingdom, according to a 2014 study. It counted about 37.2 billion neocortex neurons in the long-finned pilot whale, almost twice the human figure. The authors say neuron counts alone do not explain human cognitive abilities.
Sources for this story
- Reiss and Marino (2001), Mirror self-recognition in the bottlenose dolphin: a case of cognitive convergence, PNAS 98(10):5937-5942 — Proceedings of the National Academy of Sciences
- King and Janik (2013), Bottlenose dolphins can use learned vocal labels to address each other, PNAS 110(32):13216-13221 — Proceedings of the National Academy of Sciences
- Abramson, Hernandez-Lloreda, Garcia, Colmenares, Aboitiz and Call (2018), Imitation of novel conspecific and human speech sounds in the killer whale, Proceedings of the Royal Society B 285:20172171 — The Royal Society
- Fiorito and Scotto (1992), Observational learning in Octopus vulgaris, Science 256:545-547 — American Association for the Advancement of Science
- Kohda and colleagues (2019), If a fish can pass the mark test, what are the implications for consciousness and self-awareness testing in animals?, PLOS Biology 17(2):e3000021 — PLOS
- Mortensen and colleagues (2014), Quantitative relationships in delphinid neocortex, Frontiers in Neuroanatomy 8:132 — Frontiers
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