It enjoys life in the slow lane, congregating around seamounts (undersea volcanoes) and hills in the deep ocean.
New Zealand boasts - or boasted - the biggest concentration in the world, at fishing grounds around the Chatham Rise with smaller stocks off the West Coast and East Cape.
Valued for its delicate, shellfish-like taste and white flesh high in omega 3 oil, it can fetch prices higher than snapper, triggering an export boom in the '80s and '90s which came back to bite us.
It's scarcer than West Coast whitebait in supermarkets, due as much to demand from US consumers as the plunder of previous decades by destructive bottom-trawling.
By 2000, estimated stocks on the Challenger Plateau, west of Taranaki, had sunk to as low as 3% of the pre-fishing population, well below the "maximum sustainable yield" which guides the allowable catch set each year under New Zealand's pioneering quota management system.
The Challenger and South Island West Coast fishing grounds were closed and catch limits on the Chatham Rise have since been progressively reduced.
On a different scale is hoki: the McDonald's of the seas (it is the stuff of Filet-O-Fish) to orange roughy's restaurant trophy status.
Though worth far less per kilogram, its faster reproduction and availability at mid-ocean depths mean it can be harvested in far greater numbers.
Hoki became the pin-up fish for the quota management system in the 1990s - the promise that commercial fishing could be managed sustainably by setting targets to ensure that, on average, catches were limited to the "maximum sustainable yield" - a level which varies from 25% to 45% of the pre-fishing stock, depending on the species.
The allowable catch rises or falls from year to year, depending on Niwa and Ministry of Fisheries scientists' assessment of the health of the fishery.
Scientists know more about hoki than most species but, despite this, the western hoki stock was heading in the same direction as orange roughy a decade ago, and, by 2007, the allowable catch was down to 90,000 tonnes - about a third of the amount taken in 2000.
Amid heightened consumer interest in sustainable food supply, New Zealand's management of these species has damaged our clean, green reputation.
Both species feature in environmental groups' "fish to avoid" guides - orange roughy is at No 1 and hoki at No 5 on Greenpeace's NZ Red Fish list.
Influential newspapers The Guardian and The New York Times have cited New Zealand in critical stories and columns about "unsustainable" trawling and the impacts of bottom-trawling.
British supermarket chain Waitrose was reported last year to be boycotting New Zealand hoki. (The fact the report was misleading doesn't matter - perception is what counts.)
This year, the Trader Joe's supermarket chain in the US and Loblaw, Canada's largest retail chain, refused to sell orange roughy.
Shipping giant Maersk announced in May it would no longer carry roughy (though it rescinded after ministry lobbying).
What, in the face of this international backlash, does New Zealand do? Last month, Fisheries Minister Phil Heatley reopened the Challenger fishing ground for orange roughy and increased (for the second straight year) the allowable hoki catch.
Brave, obstinate, or quiet faith that the quota management system is working?The ministry (and fishing industry) says the QMS is grounded in science; environmentalists say the science remains as uncertain as picking Lotto numbers.
While reopening one orange roughy ground, the minister slashed the catch for the biggest roughy fishery in the world, around the Chatham Rise, amid growing evidence that stocks are in deep decline.
It was the third successive quota cut and the fishery is lurching towards closure.
The 2010/11 take will be 4840 tonnes - well below the 1980s' Chatham Rise peak of 33,000 tonnes.
Estimating the health of stocks and assessing trends is a science of variables - scientists combine survey information on the age, size and quantity of fish in the area with historical trends in survey and catch data and knowledge of the species' growth rates, spawning rates, age of reproduction and natural mortality.
More is known about some species than others and it takes years to build up the databases needed for accurate computer modelling.
Deepwater fisheries such as orange roughy have a short history and the track record in managing them worldwide is far from good.
Orange roughy don't exactly help their cause.
Acoustic monitoring is unreliable and a typical trawl survey costs $2 million.
The ministry has only a $22 million research budget for the 100 or so species (more than 600 separate stocks) in the QMS.
Adult fish are difficult to age and not enough is known about frequency of spawning and recruitment of adults into the fishery.
The reopening of the Challenger fishery follows trawl and acoustic surveying last year indicating the population has bounced back significantly in just a few years.
The stock (or biomass) is estimated to have recovered from about 20,000 tonnes in 2006 to 52,000 tonnes last year.
Curious indeed for such a slow-maturing fish.
Scientists recommended that 1000 tonnes could be caught, but Fisheries Minister Heatley opted for a more cautious 500 tonnes - not much more than can be taken for scientific research.
Environmentalists query how reliable the evidence of recovery is, given the roughy's slow growth and suspicion that recruitment of juveniles into fisheries is sporadic.
"We really need to look at the data over a couple of years rather than rely on just one estimate," says Environmental and Conservation Organisations spokesman Barry Weeber.
He notes the ministry has reopened the fishery before the population has recovered to the maximum sustainable yield (or take), about 35% of the pre-fishing population.
Adding to the unease is the continuing decline of the much bigger stocks on fishing grounds around Chatham Rise.
The population is not just below the maximum sustainable yield, it is thought to be below the "soft limit" - 20% of the unfished population - which signals the stock is depleted and triggers a rebuilding plan.
Some estimates suggest the stock is approaching the "hard limit" of 10%, which could force the closure of the world's biggest orange roughy fishery.
Weeber puts it like this: "We've done as much to orange roughy in the last 20 years as happened to the [Atlantic] cod fishery in over 300 years. You can do major things in very short periods of time with the technology you have today."
MFish chief executive Wayne McNee says it's accepted practice to let stocks fall to the soft limit before making major interventions.
He says the ministry has learnt its lesson with orange roughy.
"So when we see what's happening on Chatham Rise at the moment, we cut those catches rapidly and if we need to we will cut them further next year."
On the Challenger Plateau, McNee says there's "good, peer-reviewed scientific research telling us the stock is where we think it is".
But he concedes: "We don't actually know why, but the fish are there and continuing to become more abundant."
Weeber says while the ministry is quick to ease limits at the first sign of positive data, it tends to await several years of negative trends before reducing catches.
"We don't think the ministry is being precautionary enough in the way they are approaching orange roughy and other species."
He cites insufficient cuts to the quota this year for cardinal, another deepwater species in trouble.
Structural changes have reduced scientific input into ministry decision-making in recent years, Weeber claims.
"We are spending about half what we spent 20 years ago on fisheries' science - we're doing less general trawl surveys than 20 years ago.
"We're talking about a $1.5 billion industry and we're only spending $20 to $25 million a year on research. That's not enough. We've only got good data on probably less than 20% of the stocks in the quota management system."
Though lack of knowledge and flawed assumptions contributed to orange roughy's decline, hoki is the most studied commercial fish species and is surveyed annually.
The decline of the western stock was therefore a major PR blow for the QMS.
Though catch limits were cut in 2001, stocks reached depleted (below 20%) levels in 2003 and, by 2007, the catch was down to 90,000 tonnes - well below the 250,000 tonnes allowed in 2000.
"We were really quite disappointed in what happened with hoki," says the ministry's chief scientist, Pamela Mace.
"It was our poster child for quota assessment and management."
At least part of hoki's decline was for natural reasons - poor spawning years due to warmer seas in the early 2000s.
The fishery has now recovered to the extent the minister has increased the allowable catch to 120,000 tonnes.
"It's a shame the stock went down but management was responsive - as responsive as anywhere else in the world," she says.
Dr Mace helped develop the science systems which underpin the QMS in the 1980s before heading overseas.
She forged an international reputation in the US and Canada, ending up as national stock assessment co-ordinator for the US Marine Fisheries Service before returning to New Zealand in 2004.
She agrees it's a worry that the industry-funded research budget allows only periodic checks on some QMS stocks.
"But I'm a scientist - you can never have too much research."
While there are more than 600 fisheries, most of the total catch comes from a handful of stocks, she says.
The research budget is focused on the most highly fished and valuable species - the 119 stocks whose status is known account for two-thirds of total landings.
"There's a huge number of really small stocks where we just look at catch patterns - if there was a really major problem, we would pick it up."
Deepwater fisheries research received a 10% boost this year.
"Even if we had 10 times the research budget, we would never have close to perfect knowledge of all stocks."
A PAPER Dr Mace co-wrote in 2006 on deepwater fisheries acknowledges the tendency, whenever new stocks are discovered, to adopt a "goldrush mentality" and concedes that orange roughy stocks had "frequently been fished down too low".
But she remains optimistic that roughy (along with other deepwater species such as cardinal and oreo) can be sustainably fished - though to nowhere near past levels.
She acknowledges scientists are surprised by the 2009 survey results at Challenger Plateau.
"It's higher than we would have thought but not so much higher that it's completely unlikely."
She says there's an inevitable lag between stock assessment and management response.
"Maybe we are not quick enough off the mark in restricting or increasing quotas - but we are being as quick as we possibly can be."
Of 119 QMS stocks for which status is known, 79 were at or above target levels last year and 38 were causing concern.
The latter include the West Coast North Island snapper fishery, longfin eels, Tasman/Golden Bay scallops, porbeagle sharks, bluenose and southern blue tuna.
High-volume fisheries including ling and hake are doing well, Mace says.
Consumers should bear in mind that fish stocks fluctuate naturally and it is not unusual for stocks to dip below the maximum sustainable target at times, she says.
But it becomes a problem when there are several years of poor recruitment, as happened with hoki.
"When we reduce the quota, it's considered to be a management failure, when in fact we are being constructive."
Mace queries why "one well-managed species" (hoki) has been singled out by supermarkets when most fish are caught by trawling.
Chief executive McNee says scientists are confident that, even with a 10,000-tonne increase this year, hoki stocks will continue to rebound.
He says the ministry retains confidence in the QMS.
"We are continuing to improve the management system, continuing to learn more about the fish stocks and the way the science works and focusing on those stocks that we know have risk.
"International studies always hold it up as one of the world-leading fisheries' management systems.
"That's not to say it's perfect.
It is continuing to evolve and improve.
There are still issues around bottom-trawling and we are continuing to work on ways to mitigate the impacts on the [seafloor] environment."
