According to the scientists at University of Exeter in the UK, these abnormal behaviours have been linked to the effect of carbon dioxide (CO2) on how the brain processes signals from sensory organs.

High CO2 levels can impair the way fish behave making them swim towards predator smells instead of away and even ignoring the sounds that normally deter them from risky habitats.

CO2 levels are predicted to be 2.5 times higher in the oceans by the end of this century, researchers said.

They believe that fish farms may be the key to establishing the long-term impact of CO2 on marine life.

In the study, researchers show that farmed fish often live in CO2 conditions 10 times higher than their wild cousins.

The scientists believe that further study of farmed fish - which already provides as much seafood for human consumption as that caught in the wild - may be crucial for understanding how aquatic species will evolve to climate change.

The captive fish farm populations living in high CO2 levels already amount to "a giant long-term laboratory experiment."

"Aquaculture may provide an 'accidental' long-term experiment that can help climate-change predictions," said Robert Ellis, a climate-change marine biologist at Exeter.

"There is the enticing possibility that fish and shellfish previously grown in high CO2 aquaculture conditions over multiple generations can offer valuable insights regarding the potential for aquatic animals in the wild to adapt to the predicted further increases in CO2," Ellis said.

The aquaculture industry may also benefit from what the climate change scientists study too.

The abnormal behaviour seen in wild fish may not matter in farmed fish, as they are provided with abundant food and shelter and they have no predators to avoid.

However, while extremely high CO2 can reduce digestion efficiency in cod, recent research suggests that relatively small increases in CO2 may actually act as a growth stimulant in some fish.

The study was published in the journal Global Change Biology.