Fish are surprisingly intelligent and this has implications for animal welfare, says Australian marine biologist Culum Brown.
While people sometimes joke that fish have a three-second memory, Professor Brown said they could remember things for as long as a year.
Brown has been studying fish for 25 years and runs the Behaviour, Ecology and Evolution of Fishes Laboratory at Macquarie University in Sydney.
One of his first experiments showed fish could learn how to escape through a gap in a trawl net after experiencing the movement of the net five times.
"I actually tested those same fish about a year later and they had remembered the location of those escape routes.
"They learned really quickly and remembered it for almost a year - it's certainly a lot better than three seconds.
"That convinced me that fish are much smarter than people give them credit for."
Fish and sharks displayed complex social behaviour, Brown said.
Large groups of fish found the escape route in the trawl net faster than small groups, suggesting they learnt from each other, he said.
"Fish pass information from one generation to another, which is kind of like human culture."
Research showed smooth stingrays had "exceptionally good memories and can distinguish days of the week", Brown said.
Large numbers of stingrays gathered at sites where recreational fishers dumped fish scraps at certain times of the day and on weekends, when scraps were more abundant.
Even when foul weather meant few boats had gone out, the stingrays would be waiting for the feast they predicted would appear at the usual time, he said.
"How they do that, we don't know."
Fish could learn to avoid hooks from their own experience and from seeing other fish get hooked.
"There's social learning of hook avoidance and it lasts for up to a year."
In 2002, researchers discovered pain receptors in fish.
Brown said fish displayed obvious signs of stress, such as breathing faster, hiding and avoiding eating,
The evidence that fish experienced pain was stronger than the evidence for many mammals. There was also clear evidence that cephalopods, such as octopus and squid, and decapods, such as crayfish and shrimps, suffered pain, he said.
Animal welfare laws in many countries excluded fish, but Brown expected this to change as legislation caught up with scientific discoveries.
"You should think about fish in the same way you think about a pig or a cow or anything else."
Aquaculture is now bigger globally than the wild fish trade and Brown is helping develop welfare guidelines for the aquaculture industry in Europe.
New Zealand currently exports live crayfish and Brown predicted concerns would soon be raised about their welfare, in much the same way live cattle and sheep exports have become controversial.
The marine biologist grew up in southeast Asia snorkeling on the "most amazing reefs" and has kept fish in aquariums since he was a boy.
"One of the first things I noticed when I started keeping fish was that they only responded to me, because I fed them and we now know that fish are capable of recognising human faces."
Researchers had found fish that were taught to recognise a photo of someone from the front could also recognise them in profile.
"They not only recognise each other, but humans," Brown said.
RNZ
