New Zealand King Salmon has revealed a 42 per cent mortality rate for salmon they farmed in warm water areas in their financial year ending January 31 2022.

For the salmon towed to cooler water the mortality rate was 37 per cent.

SAFE Campaigns Manager Anna de Roo says it's an animal welfare disaster.

"If this was happening to cows or pigs there would be investigations and prosecutions," says Anna.

"Salmon are just as deserving of protection under the Animal Welfare Act, however, currently they have no code of welfare.

Mortality rates this high are completely unacceptable and it warrants a full animal welfare investigation."

Salmon in the wild would normally be able to swim to cooler waters.

Factory farms render them trapped in warmer waters. Overcrowding, an inability to escape danger, disease and heat stress kills hundreds of thousands of salmon every year.

Last summer New Zealand King Salmon made 160 trips to the Blenheim landfill to dump 1,269 tonnes of dead salmon. It currently has a resource consent application lodged to open more farms.

"Fishes feel pain and have the ability to experience positive and negative emotional states similar to other animals, but, it's clear fishes are being ignored," says Anna.

"Salmon farming is factory farming, which is inherently cruel. Argentina banned fish farming last year and Aotearoa needs to look at banning it too."

"As a starting point, farmed fishes need a code of welfare to begin addressing the terrible treatment of fishes in factory farms."