The landmark study was published last week by CSU PhD student Leia Rogers, who said she was taken aback by just how similar the personalities of fish and humans were.

She put the fish through an optimism test, where they were introduced to a door on the left that rewarded them with food and a door on the right where they would be chased around with a net.

They were then given a middle door that they had never entered before, and Miss Rogers found that naturally "shy" or recently stressed fish refused to enter the middle tank out of sheer pessimism.

Miss Rogers said this glass-half-empty mentality mirrored that of humans who had gone through depression, anxiety, or chronic stress.

"If you have a negative affective state and you've got an exam coming up, that's going to affect your performance," Miss Rogers.

"If you're the opposite type of person and you're positive and optimistic, you're going to smash it."

Miss Rogers said she related more with the shy introverted fish, especially given that she was a researcher.

Bold fish were more likely to take risks in search of food, and Miss Rogers said she had grown especially attached to a gutsy fish she named Herby.

"He was special; I liked him because he had character," Miss Rogers said.

"This study went on for three months and you get pretty close to them, because they're pretty much the only living things you're seeing during that time."

She would put little medals on the tanks of fish that successfully completed their training and passed their fish tests.

Another favourite fish of hers was Number 18, a "fish genius" who was head and shoulders above all the other fish in terms of intelligence.

"Number 18 did all the tests perfectly and was the quickest to train. He just flew through it all. He was smart, that fish," Miss Rogers said.

"If I brought people into the lab, he was the fish I would show them."

Only the bold fish were able to pass their tests, but even they sometimes failed after losing a fight with another fish and entering into a bad mood.

This was the first study of its kind into freshwater fish, and Miss Rogers said it had hard-hitting implications for the field of fish emotion.

"It's taking us in the right direction to improve fish welfare and understand their perspective a bit more," Miss Rogers said.

"It's useful to understand what those fish experience and give them more positive emotions, because that does influence their decision making."

Charles Sturt University researcher Dr Rafael Freire, who supervised the study, said these findings could revolutionise the way fisheries and conservationists handle their fish populations.

"As fisheries are trying to increase populations of native freshwater fish, we can use this to determine how we can make sure that when hatchery-raised fish are released, they have the behaviours to survive," Dr Freire said.

"Animals have to make complex decisions to survive ... and our findings suggest fish use an emotion-like process to combine all that information to make a decision."

The paper can be found on the Plos One scientific journal.