Grey mullet disease in Waipu Estuary confirmed as Myxobolus episquamalis

The Ministry for Primary Industries has confirmed grey mullet in the Waipu Estuary have a parasitic disease. Affected specimens should not be eaten or used as bait. Photo / Pete Watkins

Laboratory testing shows grey mullet in the Waipu Estuary are affected by the parasite Myxobolus episquamalis.

A Ministry for Primary Industries (MPI) spokesperson said testing has now been finalised and results confirm the fish are infected with Myxobolus episquamalis as was suspected.

The findings are consistent with initial observations of the diseased fish, the spokesperson said.

Recreational fisherman Pete Watkins was horrified when he hauled up sick young grey mullet while netting for baitfish in Northland's Waipu Estuary.

Pete Watkins, a fisherman for 35 years, was netting bait fish on December 2 in the estuary when he hauled up what he described as “weird-looking juvenile grey mullet (Mugil cephalus) covered in a calcified pus”. He delivered a sample to MPI for testing.

Watkins said he’d never seen anything like those fish. He immediately stopped netting and spent the rest of the day watching the water, where he saw “schools and schools” of similarly affected young grey mullet.

“It was really quite upsetting,” Watkins said. “I felt sorry for those poor crazy-looking fish, although they still seemed to be able to swim okay.”

Watkins noted only the small mullet in the estuary that seemed to be affected. Other species and larger mullet further upstream looked healthy.

The MPI spokesperson said the parasite is not new to New Zealand, and the biosecurity risk and human health risk is considered low.

“M.episquamalis has been found in mullet in New Zealand since at least 2013, including in the same region.

“It’s possible that it’s present in other areas in Northland where grey and yellow-eyed mullet live,” the spokesperson said.

In April this year, yellow-eyed mullet (Aldrichetta forsteri) in the Mahurangi River at Warkworth, North Auckland, were confirmed to have the disease.

MPI said: “Reports of the disease that we have received to date have been in the summer months, and we expect that the outbreak will [subside] especially once temperatures cool.

“If there was a clear and immediate risk to public health that could be linked to affected grey mullet, we would step up efforts to alert the public. At this time there have been no reports of associated illness.

Watkins said there were "schools and schools" of affected young grey mullet in the estuary. Photo / Pete Watkins

“In the meantime, our standing advice to recreational fishers remains in place: exercise common sense and do not eat fish found dead, obviously sick fish, or fish with visible lesions. Fish that look normal are safe to eat."

MPI also advised people to wash their hands thoroughly if they touch the affected fish and said they should not use fish with lesions as bait, as that can spread the disease.

The parasite causes granular lesions across the skin of the fish, which may lead to secondary bacterial infections, but has not been linked to fish deaths.

It is not known to directly infect people. However, the consumption of infected fish may pose an indirect risk to human health as the affected fish are more susceptible to secondary bacterial infections (such as Vibrio or Flavobacterium) which can make people unwell.

Sarah Curtis is a news reporter for the Northern Advocate, focusing on a wide range of issues. She has nearly 20 years’ experience in journalism, most of which she spent court reporting in Gisborne and on the East Coast.