Snapper with milky white flesh across the Hauraki Gulf, Northland and parts of the Bay of Plenty are suspected to be suffering from prolonged starvation, a Biosecurity New Zealand report obtained by Newshub says.
Since August last year, fishers have been reporting snapper - whose fillets are usually firm and almost translucent - with this milky, sometimes mushy and slimy flesh.
There have even been reports of it in some trevally.
"It is suspected that the Milky-White Flesh Syndrome seen in snapper is related to chronic malnutrition," the Biosecurity New Zealand report sourced by Newshub under the Official information Act says.
The Ministry for Primary Industries has contracted NIWA to investigate.
"We can see externally, when looking at extreme cases of these fish, they're visibly skinny, the tissue has sunken away," NIWA fisheries scientist Dr Darren Parsons told RNZ.
Food safety tests have not shown any reason why the fish would be unsafe to eat, he said.
"From what I'm hearing from fishers, though, they're not as palatable."
Parsons told RNZ the cause is not yet known, despite suggestions that trawling or sediment runoff was to blame.
"I don't see fishing having changed in a way that would contribute to this, but it's speculation at this stage."