Blue cod farms on the way? NZ scientists crack code to breeding and raising blue cod in captivity

A blue cod in the Marlborough Sounds (file photo).

A blue cod in the Marlborough Sounds (file photo).

Blue cod farms could join salmon and mussel farms in the Marlborough Sounds following a breakthrough by scientists who managed to breed and grow the fish in captivity for the first time.

Ngai Tahu Seafood and the seafood technologies team at Plant and Food Research partnered up for the research, part of a broader investigation into how to breed native fish in captivity.

About 2000 blue cod have been raised from hatchlings to fingerlings, about 5 to 7 centimetres long. Their parents were wild blue cod taken from the Marlborough Sounds.

As well as the aquaculture opportunities raised by the research it has also been mooted as a way of replenishing depleted fisheries, but fishers says habitat decline needs to be addressed first.

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The researchers had been studying both the parents and hatchlings to see how they responded to different stocking densities, population structures, light, water temperature and food sources.

Blue cod juveniles bred and raised in captivity for the first time by Plant and Food Research scientists at their Nelson ...

Blue cod juveniles bred and raised in captivity for the first time by Plant and Food Research scientists at their Nelson hatchery.

Plant and Food Research science group leader for seafood production Alistair Jerrett said fertilised eggs and larvae were moved through a series of tanks for rearing into juvenile fish.

"Having our first population of blue cod juveniles is an exciting development and shows proof-of-concept for raising blue cod for aquaculture or perhaps restocking," he said.

Jerrett said he hoped Plant and Food Research would be in a position within the next five years to be able to produce commercial pilot scale numbers of blue cod juveniles on demand.

Plant and Food Research scientist Denham Cook, left, and research technologist Warren Fantham observe the blue cod juveniles.

Plant and Food Research scientist Denham Cook, left, and research technologist Warren Fantham observe the blue cod juveniles.

These would be used for different commercial aquaculture trials, as well experiments supplementing population numbers.

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Aquaculture New Zealand chief executive Gary Hooper said the research was exciting, but it was early days when it came to the prospect of farming blue cod for aquaculture.

"It's one of a number of a small number of species being worked on for potential future development. You've got other species like scampi, kingfish and hapuku," he said.

Marlborough man Graeme Clark, a mussel farmer based in Crail Bay, said it was only a matter of time until more species of finfish were being farmed in the Marlborough Sounds.

As well as aquaculture opportunities for species other than salmon, Clark said the rearing of fish like blue cod could help boost local populations, citing research he was involved in.

Clark was involved in a trial run raising snapper in the Marlborough Sounds using juveniles supplied by Plant and Food about 10 years ago. They grew slowly, and were eventually released.

"With the snapper, we didn't have a hell of a lot, probably only a couple thousand, but we were still catching them several years later, so there's certainly potential for this to help," he said.

Recreational fishers also welcomed the research, but said the most important thing for preserving fish populations was preventing habitat decline in the Marlborough Sounds.

Blue cod sustainability advocate Hugh Shields said bottom dredging and siltation caused by land disturbance was smothering life in the Sounds.

"You can release all the fish into the wild you like, but if the habitat isn't there they're going to die or move somewhere else," he said.

Declining population resulted in the recreational blue cod fishery being closed for almost three years in Marlborough, from 2008 to 2011. The commercial fishery was also closed for the first time last year.

Shields said regulations introduced in 2015 limiting the daily catch to two fish and the minimum catch size to 33 centimetres were helping, but he questioned if it was enough to stay ahead of increasing demand.

Marlborough Recreational Fishers Association president Peter Watson he had noticed a decline since he started fishing as a 5-year-old in the 1970s, but said there were still fish around, they were just smaller.

"The Marlborough Sounds used to fish very similarly to Milford Sound, there was an abundance of big fish," he said.

"But now it's fishing more like a hatchery, there's still plenty of fish there but they're not getting to size before they're caught or die."

"If there's no action taken today then there's going to be no fish left for tomorrow."

 - The Marlborough Express


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