Cat owners who feed their pets with fish are contributing to overfishing, which is threatening fish stocks worldwide, a scientist at an Australian university said.

Dr Giovanni Turchini of Deakin University said the global cat food industry each consumes 2.48 million metric tons of forage fish - small, rapidly breeding fish that are eaten by larger fish - each year.

"In Australia, pet cats are eating an estimated 13.7 kilograms of fish a year, which far exceeds the Australian [human] average per capita fish and seafood consumption of around 11 kilograms," Dr Turchini said.

He said the pet food industry is increasingly marketing luxury food products containing "a significant amount of fish that may be suitable for direct human consumption."

"Our pets seem to be eating better than their owners," he said.

With fishing rates exceeding replacement rates in many parts of the world, and large government subsidies boosting mass commercial fishing, many scientists see overfishing as the main threat to marine ecosystems worldwide.