Cuttlefish number sense better than a one-year-old human, research shows

New research suggests cuttlefish can not only count better than a one-year-old human, but they also prefer quality over quantity when it comes to food.

A study of 54 one-month-old cuttlefish hatched in captivity was carried out by Tsang-I Yang and Chuan-Chin Chiao, researchers at the National Tsing Hua University in Taiwan.

Their findings suggest that cephalopods count potential prey such as shrimps, crab and fishes, and make several judgment calls in deciding whether or not to strike.

Presented with different numbers of live shrimp, the cuttlefish showed consistent preference for the larger quantities, suggesting they had “number sense”.

The researchers also found that the density of the group of the shrimp did not affect their decision, and that cuttlefish took longer to decide when the numbers were higher.

This indicated that the cephalopods were taking time to count the individual shrimp of each option, rather than making an assessment at a glance.

They pointed to similar studies of one-year-old humans, which found that babies could distinguish between one and two items, and two and three items, but no higher. Rhesus macaque monkeys could judge quantities of only up to four.

With cuttlefish able to distinguish between one and five and four and five, the researchers concluded that they “are at least equivalent to infants and primates in terms of number sense”.

Given the choice between one live shrimp and two dead shrimp, the cuttlefish also opted for the smaller quantity.

The researchers were particularly struck by their response to the choice between one large live shrimp and two small live shrimps, which depended on the state of their appetite.

If the cuttlefish was hungry, it chose the single shrimp; if it was not hungry, it chose the two smaller shrimps.

The researchers concluded that this was a strategy of risk minimisation, with one shrimp in a group posing less of a threat than targeting one lone prey, and “probably an ecologically rational solution to the widespread problem of choice”: “For example, humans become more risk tolerant in their monetary decisions, as they get hungry.”

The study on “number sense and state-dependent valuation in cuttlefish” was published by the Royal Society in late August.

With the most complex brains of any invertebrate, cephalopods – a family that includes octopus and squid – are known for their sophisticated cognitive behaviours, including the ability to change colour in milliseconds.

Earlier this year, Australian researchers found that cephalopod numbers the world over were steadily increasing, potentially as a result of warmer ocean temperatures and reduced fish populations.