"Just an ugly fish that doesn't belong here."

That's how William Anaru describes the bullhead catfish.

"People have been in tears" since the invasive pest species was found in Lake Rotorua last month, he says.

Until then, biosecurity efforts led by the Bay of Plenty Regional Council and the Te Arawa Lakes Trust were focused on containing and eradicating the species in Lake Rotoiti.

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"To us, the lake [Lake Rotorua] is a person – and she's already suffered enough."

Anaru co-ordinates a group of volunteers to help cull the species.

He began recruiting boaties and Te Arawa hapū at the start of the 2018 trout season, and now has about 100 people helping rid Rotoiti of the hardy North American species.

Now he's looking to expand the Rotoiti Catfish Killas group to target catfish in Lake Rotorua.

Kia ora Whanau, I te ra 18 Tihema 2018, i kitea e matau te Ka Poti ki Rotorua nui a Kahumatamoemoe. Ki te taha o...

Posted by Rotoiti Catfish Killas on Tuesday, 18 December 2018

Anaru has volunteers coming from as far afield as Auckland and Wellington but the group needs more.

"It's not the catfish's fault they're here, so we still want to offer them a humane death.

"But it's important to get rid of as many catfish as possible as they are a threat to native fish and their eggs. We have to try and give our native lake species a fighting chance."

Anaru would like to get nets for all the local marae so they can set and check them daily.

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"Some people live right on the lake and do it every night, while others do it when they can. Every little bit helps."

The volunteer nets having been catching up to 1000 catfish a week.

 Adult catfish. Photo / File
Adult catfish. Photo / File

The volunteers also help out with public education at boat ramps and marae.

Anaru has also arranged for rangatahi to work at Lake Rotoiti as part of their community service.

The programme is part of the Te Arawa Lakes Trust's responsibility for the kaitiakitanga of the lakes.

"This means looking at everything from water quality, research and climate change, through to the sustainable management of the freshwater fishery – including our freshwater taonga such as kōaro, kōura, tuna, kākahi, inanga and morihana.

"Our world has already lost so many of our native species and it's imperative that we all do as much as we can to protect them – including from predator species such as catfish," Anaru said.

The regional council has provided the trust with 40 fyke nets to trap the fish and has also developed a digital app that volunteers use to record catfish numbers.

This helps biosecurity staff stay informed about the volunteers' work.

"We hope Lake Rotorua might still be cleared if people get stuck in early enough. One thing that will make a big difference is public help."

And in case you were wondering, catfish don't make for good eating.

Anaru has tried it and said they were not very tasty and had the texture of eel.

How to stop the spread
Before you leave a lake, waterway or river, make sure you remove all weeds from your boat trailer and gear and check for catfish.
Empty any lake water or ballast you may be carrying.
Don't leave your trailer in the water.
If you want to help in the netting programme, contact William Anaru on william@tearawa.iwi.nz or go to the Rotoiti Catfish Killas Facebook page.

What are catfish?
Nobody really knows why catfish were introduced into New Zealand, but they came here in the 1870s from North America. They are now widespread in the Waikato river system and North Island lakes, including Taupō.
Catfish can live in a wide range of temperatures and low quality water.
They can survive for long periods out of water, about 48 hours.
Catfish prey on small native fish and eat fish eggs.
They eat and compete with kōura (freshwater native crayfish).
Catfish also stir up sediment.
The Department of Conservation wants anyone catching catfish to kill them, and not return them to the waterway.