North Island researchers say they have made a significant breakthrough in the commercial farming of whitebait. Delwyn Dickie reports.

Whitebait lovers have good news. A fish breeding breakthrough by researchers at Warkworth, north of Auckland, is being claimed as a big step forward in farming the delicious little wrigglers - so much so that they envisage the day when whitebait could be picked up at your local supermarket, and possibly exported.

While they may not be the first to have cracked the method of breeding the giant kokopu - one of the five native fish whose young we collectively call whitebait - researchers at Mahurangi Technical Institute have managed it on a large scale.

They don't believe their breeding programme will bring an end to fishing for the little critters in the wild, but they do see it as a serious business opportunity, which will also take some pressure off the wild population.

The private institution specialises in the development of freshwater fish breeding techniques for commercial and conservation purposes.

Its years of research under head scientist and eel specialist Tagried Kurwie, on the breeding of the New Zealand short-finned eel as a commercial fish stock, has seen them gain international recognition.

Institute director and founder Paul Decker had always thought eel breeding research would be their big success story.

They are tantalising close to developing a technique to breed these animals in a closed life cycle, something that could also help wild eel populations, which have plummeted internationally.

But so far it has eluded them.

The breakthrough in giant kokopu breeding has taken five years of research and trials, mostly by aquatic scientist Quentin O'Brien. The magnitude of their success has left them stunned.

"They're eating us out of house and home," Mr Decker says. "With one female able to produce 20,000 eggs, which only take 27 days to hatch, we've got hundreds of thousands and are running out of containers to put them all in. We've got a tsunami on our hands."

While kokopu are only one of the fish species that make up whitebait, they are the tastiest. That makes the success of breeding them as a commercial stock so appealing, special projects manager David Cooper says.

There are two other kokopu species in the mix - banded and shortjaw, along with inanga and koaro. The giant kokopu fish are the longest-lived of the whitebait species at around 30 years. They don't develop the strong fishy taste of the other shorter-lived species until much later. So the more giant kokopu in the mix, the better the quality.

Understanding how the fish breed in the wild was a big part of their success, Mr Cooper says. That will also make it easier to supply the eggs to prospective fish farmers.

The parent fish live in gently flowing, overgrown streams, swampy lagoons and lake edges. They swim down to the lower reaches or wetlands and on a particularly high tide lay their eggs in the long grass on stream edges. These are safe from water predators like eels, but are still kept moist in the grass. The eggs hatch after a month, at the time of the next extra-high tide, and are swept out to sea.

It's thought the hatchlings stay within a few kilometres of land for about three months before heading back to shore and up streams, dodging whitebaiters and their nets as they go.

The eggs' peculiarities make it easy to supply them to prospective farmers as they won't need to be shipped in water with the accompanying special handling needs and weight. Farmers will be able to order their eggs and 10 weeks later have whitebait to sell, Mr Decker says. Three fish farmers are already interested, he adds.

The conservation of freshwater native fish is at the heart of the institute's aquaculture department research. Mr Decker says that the laying of its eggs in grass helps to explain the decline of the giant kokopu, and why fencing stock from and cleaning up waterways is important.

Massey University freshwater scientist Mike Joy says poor water quality is the main reason for the decline in native fish numbers, but is sceptical that commercial farming can help dwindling numbers in the wild and may even create problems of its own.

Besides targeting water quality, Dr Joy has called for tighter restrictions on whitebaiting, and a ban on commercial fishing of the wild stock. Four out of five whitebait species are on the official Department of Conservation threatened species list.

He argues that a commercial fish farming model is not an environmental solution for the species and points to what he says are serious issues surrounding the feeding of farmed fish using meal and oils that generally come from wild fish stocks.

Mr Cooper says that many of the breeding techniques for the giant kokopu will be transferable to the other whitebait species, and repopulating freshwater streams with kokopu is being looked at.

First up will be Tawharanui Regional Park near Warkworth, where a few hundred giant kokopu are likely to be released in the next couple of years.

Once a population has gone from a stream, young fish won't repopulate on their own, Mr Cooper says.

They need the scent of an established population in the stream before they will venture up it. Otherwise they think there must be something wrong with the area and steer clear of it.

So large fish need to establish in the streams first, to draw youngsters.

But for now, getting a business plan sorted is next on the list, Mr Decker says, with the institute expecting it should be able to start supplying the eggs properly by early next year.

Dr Joy hopes the prospect of commercial farming won't make people complacent about over-fishing as another whitebait season approaches, running in Southland from August 15 until November 30.

- © Fairfax NZ News

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